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First-order magnetic transition induced by structural transition in hexagonal structure
Journal of Magnetism and Magnetic Materials 494 (2020) 165821
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Research articles
First-order magnetic transition induced by structural transition in hexagonal structure ⁎
T
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Chaocheng Liua, Xucai Kana, , Xiansong Liua, , Shuangjiu Fenga, Jiyu Hua, Wei Wanga, Khalid Mehmood Ur Rehmana, Mudssir Shezada, Lei Zhangb a b
Engineering Technology Research Center of Magnetic Materials, School of Physics & Materials Science, Anhui University, Hefei 230601, People’s Republic of China High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China
A R T I C LE I N FO
A B S T R A C T
Keywords: M-type hexaferrites Structural transition First-order AFM transition Thermal hysteresis
Herein, A first-order antiferromagnetic (AFM) phase transition is observed in SrFe12O19 hexaferrites, the detailed analysis has been investigated systematically by magnetic measurements and confirmed it depend on magnetic field. Interestingly, the original peak appear in variable temperature X-ray diffractions, and structural transition change from space group P63/mmc to P-62c around critical temperature without destroying hexagonal crystal system, which is illustrated to be the driving force to result in first-order AFM transition. Furthermore, An apparent phenomenon of magnetic phase transition exhibits in M(H) curves, some characteristic properties of critical temperature and field are specifically correspond to the one of thermal hysteresis and structural transition, suggesting the strong coupling between structural and magnetic transition.
1. Introduction Magnetoplumbite-type hexaferrites compounds with a formula MFe12O19 (M = Ba, Sr, Pb, Ca, etc.) have been studied extensively due to the significative properties they exhibited, such as magnetocaloric effect (MCE) [1], magnetostriction (MS) effect [2], giant magnetoresistance (GMR) effect [3], microwave absorption effect, high maximum energy product and large uniaxial magnetocrystalline [4]. Besides, Mtype strontium hexagonal ferrites always maintain a significant research topic in materials sciences, and also are useful in permanent magnets, magnetic storage media, electromagnetic wave absorbers, high-frequency devices and absorbers of the EMR [5]. In this compounds, Sr, Fe and O ions formed two kinds of close-packed blocks (S blocks and R blocks), the crystal structure of MFe12O19 belongs to closepacked hexagonal packing structure, which are composed of S and R blocks along the hexagonal c-axis according to an order sequence of spinel block (S = Fe6O82+) and hexagonal block (R = MFe6O112−) [6]. There are two oxygen ion layers in spinel block while hexagonal block possess three, and these five oxygen ion layers make up all three different interstice (tetrahedral interstice, bipyramidal interstice and octahedral interstice) [7]. Among that, all five Fe3+ ions are distributed in these three interstitial orbits formed by oxygen ions in each unit cell, they are 4f1 (tetrahedral site), 2b (bipyramidal site), 2a, 12k and 4f2 (octahedral site), where the magnetic moment of Fe3+ ions in 2a, 2b
⁎
and 12 k sites are spin up, yet 4f1 and 4f2 sites hold the magnetic moment spin down [8]. The upward magnetic moments have a positive effect on magnetization, while the downward one will lead to a decrease in magnetization, and the Fe3+ in different interstitial orbits can achieve superexchange interaction through oxygen atom (Fe3+–O–Fe3+), which are determined to be the major origin of magnetism [9]. Not hard to find that once crystal structure of MFe12O19 transformed, it will certainly result in some changes in magnetism to some extent based on the analysis of the magnetoplumbite-type hexaferrites structure above. For this purpose, it is worthwhile and interesting to investigate the connections between structural phase transition and magnetic phase transition. Recently, the investigation of structural phase transition has been proved to be the hotspot for theoretical research, attracted more and more attention and recognition as well. In general, structural transformation usually occurs in relatively simple crystalline systems with high symmetry, such as cubic system. One such typical case is the ternary intermetallic compounds AXM3 (A = Ga, Al, Sn, Zn, Cu, In, Ge, etc.; X = C, N; M = Mn, Fe, Co, Ni, etc.), which subordinate to antiperovskite structure [10–12]. In these intermetallic compounds, structural phase transition can be observed frequently and magnetic phase transition is most often occurred induced by it. However, for M-type hexaferrites, the phenomenon of structural phase transition cannot be observed easily, let alone the appearance of magnetic phase transition.
Corresponding authors. E-mail addresses: [email protected] (X. Kan), [email protected] (X. Liu).
https://doi.org/10.1016/j.jmmm.2019.165821 Received 12 August 2019; Received in revised form 5 September 2019; Accepted 9 September 2019 Available online 11 September 2019 0304-8853/ © 2019 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials 494 (2020) 165821
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Certainly, the occurrence of the sharp peak also can be associated with the effect of the magnetic domain wall motion according to the literature [20]. For ZFC curve, the magnetic domain are blocked randomly in zero applied field along the oriented easy directions, and the net magnetization will be established due to the 180° domain wall flip toward to the direction of the applied field. Even so, there are still some domain walls pinned owing to the complicated microstructure in the system, and can be unpinned through thermal activation [21]. Under this circumstance, executing the measurement process with increasing temperature will cause two phenomenon occur in the curve: One is the usual drop in magnetization (Ms) because of the thermal agitation, and another is the little increase in Ms due to the unpinning of the domain walls and flip into the direction of the applied field as increasing temperature [22]. According to the literature reported by A.M. Alsmadi [22], the effect of competition between domain wall unpinning (i.e. easy domain wall motion) and thermal agitation of spins will lead to a peak in ZFC curve, while an apparent sharp peak in this work is much higher than that one. Therefore, we prefer the theory of magnetic phase transition, and subsequently verify this result by other relevant measurements and elaboration. The separation of FCC and FCW branches of M(T) shows the occurrence of thermal hysteresis within this temperature region, indicating the potential characteristics of magnetic phase transition according to the literature report [16,23]. Fig. 1(b) gives the FCC and FCW curves with the magnetic field of 0.1 kOe, 1 kOe and 10 kOe. As shown, an apparent division appear in magnetic field of 0.1 kOe, the longitudinal span between FCC and FCW branches of M(T) is narrowed significantly at 1 kOe and coincide completely as the magnetic field up to 10 kOe. For the further study on the magnetic field dependent thermal hysteresis, Fig. 1(c) shows the FCC and FCW curves with more detailed magnetic field range from 1.5 kOe to 8 kOe. Apparently, this two branches overlap basically starting with a magnetic field of 1.5 kOe and until they coincide completely under higher magnetic field. That means thermal hysteresis disappear almost as the magnetic field reaches 1.5 kOe, we argue that this magnetic field is the critical field to start to achieve the constraint of antiferromagnetic effect and ferromagnetic effect recovery the dominance gradually in the following illustration [24]. In addition, the sign of thermal hysteresis vanish gradually as we change the magnetic field strongly, this explains the possible AFM-FM phase transition depends not only on temperature but also on magnetic field. To better understand the nature of magnetic phase transition in the sample, Fig. 2(a) gives initial M-H curves to explain magnetization dynamics. All initial isothermal magnetization display the complete dynamic magnetization process at the interval of 5 K. A distinct mutation region occurs in the curve around the 2000 Oe − 5000 Oe range, this may be caused by the AFM-FM transition based on the above analysis. Meanwhile, the hypothesis cannot be ruled out the possibility due to the growth of magnetization as a result of domain wall motion and domain rotation in a system having domain wall pinning [25]. Fig. 2(b) gives the slope for initial M-H curves around the temperature near phase transition. As shown, we choose the slope region through the whole phase transition field (around 1000 Oe – 10,000Oe) as nine parts to linear fitting. And the slope can be expressed as:
This circumstance is attributed to the structural type, MFe12O19 hexaferrites possess close-packed hexagonal structure (space group P63/ mmc, No. 194) [13,14], and the symmetry of this structure is much lower than that of cubic system. Besides, the magnetocrystalline anisotropy of MFe12O19 belong to uniaxial type, which is different from the planar one for cubic crystal system [15], all these distinctions will lead to the difficulty of structural phase transition in magnetoplumbite-type hexaferrites. Consequently, exploring and investigating the internal coupling between magnetism and structural phase transition of MFe12O19 will be full of novelty and challenge, and some interesting characteristics are expected to appear in MFe12O19. In this paper, we have successfully synthesized SrFe12O19 hexaferrites compounds and found the obvious evidence for first-order phase transition. Detailed researches and investigations of phase transition for SrFe12O19 indicated that varying temperature result in structural transition, and it further triggered the appearance of magnetic transition. The phenomenon of thermal hysteresis obviously exists in field-cooled cooling (FCC) and field-cooled warming (FCW) processes, illustrating the occurrence of first-order magnetic transition in SrFe12O19 hexaferrites [16]. Meanwhile, a first-order antiferromagnetic (AFM) phase transition induced by structural transition is confirmed in SrFe12O19, the competition between antiferromagnetic-ferromagnetic (AFM-FM) is observed and the dominant effect of AFM reaches strongest around 323 K (TN) [17]. It is also worth mentioning that magnetic phase transition begins to occur around 270 K in the process of variable temperature magnetic measurement, which is basically consistent with the onset temperature of thermal hysteresis. 2. Experimental details Polycrystalline sample of SrFe12O19 hexaferrites powders were synthesized by the conventional ceramic method. SrCO3 (Aladdin) and Fe2O3 (Aladdin) raw materials were weighted according to stoichiometric ratio and mixed in planetary mill (Pulverisette; Fritsh GmbH, Germany). The whole mixing process lasts for 3 h with an angular velocity of 300 revolutions per minute, then take out the mixture slurry and dry it. Finally, presintering the prepared sample at 1523 K for 2 h and good-quality sample could be obtained. The information of phase compositions and structure were detected by variable temperature Xray diffraction (Rigaku-TTR3) with Cu Kα radiation from 300 K to 500 K. The Rietveld refinement of XRD data was carried on Rietica software to fit the phase and structure information. The crystal structure diagram were built by Materials Studio and Vesta software. The differential scanning calorimetry (DSC) were performed thermal behavior of the sample. The variable temperature magnetic properties were analyzed by a Quantum Design superconducting quantum interference device magnetic property measurement system (SQUID-MPMS 3) from 250 K to 390 K with applied field 30 kOe. 3. Results and discussion Fig. 1 shows the temperature dependent magnetization M(T) curves for SrFe12O19 hexaferrites compounds. Fig. 1(a) presents the zero-fieldcooled (ZFC), field-cooled cooling (FCC), and field-cooled warming (FCW) processes with the temperature between 200 and 380 K at a magnetic field of 0.1 kOe. Obviously, The ZFC curve undergoes an abnormal sharp raise peak with increasing temperature, which directly demonstrate there are some abnormal magnetic competition in this system [18]. M-type strontium hexaferrites can be described as the compound body of antiferromagnetic and ferromagnetic, it is all due to the truth that SrFe12O19 has both spin-up and spin-down magnetic moments. That is to say, the characteristic of antiferromagnetic (AFM) and ferromagnetic (FM) coexist in the system, Hence, the bulging peak may can be attributed to the result of competition between antiferromagnetic and ferromagnetic (AFM-FM), and this temperature is defined as the Néel temperature (TN) [19].
K = (M2 − M1)/(H2 − H1) = ΔM /ΔH
(1)
Here, M and H are magnetic parameters in initial M-H curves. According to the concept of second order phase transition [26]: Secondorder phase transition, or “second-order phase transition” or “continuous phase transition”, is mainly due to the fact that the curve of the rate of change of free energy (or other ordered parameters, such as magnetization) to temperature (or other parameters, such as magnetic field), remains continuous and does not change abruptly. Quite evidently, Fig. 2(c) reveals a discontinuous slope curve as the plot change abruptly around the region of magnetic phase transition field. This is 2
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Fig. 1. Temperature dependent magnetization M(T) curves of SrFe12O19 hexaferrites with different magnetic fields (0.1 kOe ≤ H ≤ 10 kOe).
where a and b are temperature-dependent [28]. For the condition of equilibrium (∂G/∂M = 0, i.e., energy minimization), the magnetic equation of state evolves into bellow [27]:
more direct argument to illustrate that this magnetic phase transition ought to be first order phase transition. M2 vs H/M are plotted in Fig. 3. It can be seen clearly that all lines of M2 versus H/M are converged at origin and parallel to each other in high field region. According to the Landau theory of phase transition, the Gibbs free energy G can be expressed by following equation in terms of the order parameter M as [27]:
G (T , M ) = G0 + aM 2 + bM 4 − −MH
H / M = 2a + 4bM 2
(3)
Ordinarily, M2 versus H/M should be a series of straight line paralleled to each other in the high field region. On the Basis of the criterion proposed by Banerjee [29], the slope of straight line in Arrott
(2)
Fig. 2. The initial magnetization curves for SrFe12O19 hexaferrites (the inset part is an enlargement region of phase transition and the variety of linear fitting). 3
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peak can be clearly observed in this enlarged region. The occurrence of original phase in the patterns provides the most direct evidence for the existence of structural phase transition from one phase to another phase with a mixed phase in some intermediate temperature [2,31]. Especially, the new and original characteristic peak appear in the transition from 320 to 330 K, and then disappear in the XRD patterns as temperature exceeds 410 K. This variation tendency is in well agreement with the result of first-order antiferromagnetic (AFM) phase transition, and the temperature of structural phase transition closely correspond to the magnetic transition temperature dominated by antiferromagnetic effect [32]. It is worth mentioning that the shrink of Bragg’s peak also may lead to an appearance of weak sharper peaks, but it is not very suitable for this XRD pattern as an obvious evolution of the intensity peak. From what has been discussed above, a first-order antiferromagnetic (AFM) phase transition and structural phase transition are inevitably related to some extent, that is, structural phase transition leads to the occurrence of magnetic phase transition, and we give the further explanations in the following crystal structure studies to figure out this assertion. In order to study the detailed transformation of crystal structure, we select the diffraction patterns before and after the transition at 300 K and 350 K to perform the Rietveld refinements respectively. As revealed in Fig. 5(a), the Rietveld refinement of room-temperature XRD pattern accepts a close-packed hexagonal packing structure (space group: P63/ mmc), while Fig. 5(c) exhibits the pattern of SrFe12O19 hexaferrites with the space group: P-62c at 350 K. Apparently, varying temperature lead to the phase transition in crystal structure, space group change from P63/mmc to P-62c. In addition, Fig. 5(b) and Fig. 5(d) display the sketch diagram of the crystal structure at 300 and 350 K separately. Clearly, there are some specific O atoms changed in lattice sites and occupy different positions compared 300 with 350 K in the crystal structure. Undoubtedly, changed O atoms will cause the variation of interval space type and occupancy of Fe atoms, this behavior theoretically becomes the essential and original factor that does render the magnetic phase transition possible [33]. Fig. 6 shows the detailed interval types and atomic occupancy for SrFe12O19 from top and bottom perspectives at 300 and 350 K. As clearly depicted, The O atoms occupy the convergence of three octahedral interstice viewed from the top and bottom at 300 K, but occupy the vertex of tetrahedral interstice at 350 K. This evident change cause
Fig. 3. The Arrott plot: isotherms of M2 versus H/M.
plot can be used to determine the order of the magnetic transition: the positive slope match with the second order transition while the negative slope corresponding to the first order transition. Undoubtedly, the slope of Arrott plot imply second magnetic transition in the sample at high field, while a negative slope in Arrott plot can be detected as semicircular shape at the initial region, it also directly suggest that the magnetic phase transition should be defined as first order transition according to the Banerjee criterion. This determination is in agreement with the analyses of M2 vs H/M reported by P. Zhang et al [30]. Through a series of discussions above, we firmly believe that there is a first order magnetic phase transition in SrFe12O19 hexaferrites. In order to explore the possible motivation of magnetic phase transition, the further analyses for structure phase are minutely depicted. Fig. 4(a) exhibits the temperature dependent X-ray diffraction patterns with the temperature from 300 to 500 K. It is absolutely essential to point out that the XRD pattern at 300 K is standard pure phase for SrFe12O19 hexaferrites. On the whole, all XRD patterns are similar at different temperature, but there are some new phase begin to appear in XRD patterns at 330 K and disappear at 440 K. Fig. 4(b) gives the locally amplified XRD spectra around 2θ = 50° − 52°, and the characteristic
Fig. 4. Variable temperature X-ray diffraction patterns for SrFe12O19 under warming measurement from 300 to 500 K. 4
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Fig. 5. The Rietveld refined X-ray diffractions at 300 and 350 K for SrFe12O19 hexaferrites and corresponding crystal structure respectively.
crystal structure phase transition should be the reason why the firstorder antiferromagnetic (AFM) phase transition exists in SrFe12O19 hexaferrites compounds [2]. Fig. 7 shows the differential scanning calorimetry (DSC) curve of
the transformation of atomic site occupation indeed, and the specific occupancy of atoms in each orbit are listed in Table 1. As known, performance is usually determined by structural characteristics. Accordingly, through the above research work of structure transition, the
Fig. 6. The interstitial structure of top and bottom perspectives for SrFe12O19 hexaferrites at 300 K and 350 K. 5
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Table 1 The atomic occupancy of SrFe12O19 hexaferrites crystal structures under 300 K (out brackets) and 350 K (in brackets). Atom
Sr Fe Fe Fe Fe Fe O O O O O
Wyckoff
2d 2a 4e 4f 4f 12 k 4e 4f 6h 12 k 12 k
300 K:P63/mmc─(350 K:P-62c) x/a
y/b
z/c
Occupancy
0.6667(0.3333) 0(0) 0(0) 0.3333(0.3333) 0.3333(0.3333) 0.1689(0.1689) 0(0) 0.3333(0.3333) 0.1817(0.1817) 0.1565(0.1565) 0.5047(0.5047)
0.3333(0.6667) 0(0) 0(0) 0.6667(0.6667) 0.6667(0.6667) 0.3378(0.3378) 0(0) 0.6667(0.6667) 0.3634(0.3634) 0.3130(0.3130) 1.0094(0.0094)
0.25(0.75) 0(0) 0.2542(0.2458) 0.0272(0.0272) 0.1909(0.1909) −0.1093(0.6093) 0.1516(0.1516) −0.0552(0.5552) 0.25(0.25) 0.0527(0.0527) 0.1508(0.1508)
1(1) 1(1) 0.5(0.5) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1)
Fig. 7. Differential scanning calorimetry (DSC) of SrFe12O19 hexaferrites.
transition from 270 K to 390 K, performed as the shape of outward bulge in the curve, the onset temperature of magnetic phase transition is coincided well with the that of thermal hysteresis [37]. Another significant feature is that all curves of the magnetic phase transition are driven around 1.5 kOe, This critical magnetic field are also well consistent with the one that thermal hysteresis begins to disappear (see Fig. 1). Probably, a first-order antiferromagnetic phase transition start to subside around 1.5 kOe, which means, a larger magnetic field is needed to restrain the orientation of reverse magnetic moment, and force it complete the process of AFM-FM phase transition [24]. This transversion demands for higher magnetic field to make the curves to meet saturation, and shown as an obviously mutation in hysteresis loop diagram [38]. Besides, structural transition may force the change of domains in SrFe12O19 hexaferrites magnetic structure, some easily oriented magnetic moments inside the domains are able to turn over toward to the same direction with low external field [39]. Nevertheless, part of difficult-oriented moments will not be affected by low magnetic field, but by high magnetic field. Only the magnetic field reaches the critical value, can the orientation of tough moments inside the domains be achieved. This divergence in the difficulty of orientation results in the occurrence of magnetic phase transition presented as the shape of outward bulge in hysteresis loops.
SrFe12O19 hexaferrites. It can be seen that the obtained thermoanalytical curve has two exothermic effect peaks at 246 K and 337 K respectively. The continuous downward trend at the beginning of the curve can be attributed to the heating process in a crucible [34]. These two specific exothermic peaks is associated with the magnetic and structure phase transition point of SrFe12O19 hexaferrites. The changed heat flow in DSC plot imply the existence of first order transition, this indeed verify the structure phase transition in SrFe12O19 as an occurrence of evident change in heat [35]. Moreover, it is only possible that the appearance of magnetic phase transition is induced by structure transition due to the coincidence of all temperature and field parameters, and the magnetic phase transition can be surely classified as first-order transition as changed heat flow. Fig. 8 displays the M(H) curves under different temperature in the scope of 250 K to 390 K. On the whole, all branches exhibits the typical characteristics of magnetic hysteresis loop, while a conspicuous bulge appear on the curve within a certain extent of magnetic fields. Since the pinning effect of domain wall motion can be excluded definitely by a systematically analyses above, this irregular inflection occurred in the curves indicates the existence of magnetic phase transition in SrFe12O19 hexaferrites [36]. As the enlarged region shown in the lower right corner of Fig. 8, the curve exhibits the characteristic of magnetic 6
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Fig. 8. Magnetic hysteresis loops for SrFe12O19 hexaferrites under varying temperature process from 250 K to 390 K.
Fig. 9. The magnetic phase diagram of H versus T for SrFe12O19 hexaferrites.
Regardless of magnetic field of temperature, the diagram of H versus T is fitted precisely with the phase transition results of structure and magnetism verified above, which interpreted the precision and reliability of first-order phase transition appeared in SrFe12O19 hexaferrites.
The magnetic phase diagram of SrFe12O19 hexaferrites is constructed in Fig. 9 to show the process of phase transition in detail. As shown, the graph can be divided into three parts: AFM region, AFM transition region and FM region. The critical field and constrained field of different temperature are marked in the diagram to reflect the starting and terminating field of antiferromagnetic dominant effect. The area between critical and constrained field is the AFM transition region, the properties of this part are same as the magnetic field values in Fig. 1, where the thermal hysteresis begins and ends at. The critical temperature of structure phase transition is also labeled in Fig. 9, the space information of structure for SrFe12O19 with different space group around critical temperature are given in the picture as well, detailed sketch map of crystal structure have been listed and discussed above.
4. Conclusions In summary, the synthesis, structure and magnetic properties of hexagonal SrFe12O19 compounds have been investigated systematically. Exhilaratingly, a first-order antiferromagnetic (AFM) transition is observed by the thermal hysteresis between FCC and FCW branches, and this first-order transition rely on magnetic field embodied in M(T) curves obviously. The plot of initial M(H) and M2 versus H/M give a 7
Journal of Magnetism and Magnetic Materials 494 (2020) 165821
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convinced evidence to certify this result. The characteristic of first order structural transition is verified by variable temperature X-ray diffraction and thermal behavior, and the crystal structure around the phasetransition temperature confirm the existence of structural transition, which is demonstrated should be the driving force to compel the firstorder AFM transition. Additionally, typical magnetic phase transition is performed in M(H) curves around critical field and temperature, and the H versus T is constructed by internal crucial parameters exhibited in variable temperature hysteresis loops. It is necessary to emphasize that the properties of first-order AFM and structural transition are well matched respectively, indicating a strong coupling between structural and magnetic transition.
[15]
[16] [17]
[18]
[19]
[20]
Acknowledgments [21]
This work was supported by the National Natural Science Foundation of China (Nos. 51872004, 51802002), Education Department of Anhui Province (Nos. KJ2013B293, KJ2018A0039). In addition, the authors thank Professor Lei Zhang for his help in the X-ray diffraction measurements.
[22]
[23]
[24]
References [1] K. Shi, Y. Sun, C.V. Colin, L. Wang, J. Yan, S. Deng, H. Lu, W. Zhao, Y. Kazunari, P. Bordet, C. Wang, Investigation of the spin-lattice coupling in Mn3Ga1−xSnxN antiperovskites, Phys. Rev. B. 97 (2018) 054110. [2] L. Zu, S. Lin, Y. Liu, J.C. Lin, B. Yuan, X.C. Kan, P. Tong, W.H. Song, Y.P. Sun, A first-order antiferromagnetic-paramagnetic transition induced by structural transition in GeNCr3, Appl. Phys. Lett. 108 (2016) 031906. [3] S. Lin, H.Y. Lv, J.C. Lin, Y. Huang, L. Zhang, W.H. Song, P. Tong, W.J. Lu, Y.P. Sun, Critical behavior in the itinerant ferromagnet AsNCr3 with tetragonal-antiperovskite structure, Phys. Rev. B. 98 (2018) 014412. [4] Y. Yang, F. Wang, J. Shao, D. Huang, H. He, A.V. Trukhanov, S.V. Trukhanov, Influence of Nd-NbZn co-substitution on structural, spectral and magnetic properties of M-type calcium-strontium hexaferrites Ca0.4Sr0.6-xNdxFe12.0-x(Nb0.5Zn0.5)xO19, J. Alloys Compd. 765 (2018) 616–623. [5] S.V. Trukhanov, A.V. Trukhanov, V.A. Turchenko, A.V. Trukhanov, E.L. Trukhanova, D.I. Tishkevich, V.M. Ivanov, T.I. Zubar, M. Salem, V.G. Kostishyn, L.V. Panina, D.A. Vinnik, S.A. Gudkova, Polarization origin and iron positions in indium doped barium hexaferrites, Ceram. Int. 44 (2018) 290–300. [6] C. Liu, X. Liu, S. Feng, K.M.U. Rehman, M. Li, C. Zhang, H. Li, X. Meng, Effect of YLa-Co substitution on microstructure and magnetic properties of M-type strontium hexagonal ferrites prepared by ceramic method, J. Magn. Magn. Mater. 445 (2018) 1–5. [7] J. Kreisel, H. Vincent, F. Tasset, M. Pate, J. Ganne, An investigation of the magnetic anisotropy change in BaFe12−2xTixCoxO19 single crystals, J. Magn. Magn. Mater. 224 (2001) 17–29. [8] L. Lechevallier, J.L. Breton, J. Teillet, A. Morel, F. Kools, P. Tenaud, Mössbauer investigation of Sr1−xLaxFe12−yCoyO19 ferrites, Phys. B Condens. Matter. 327 (2003) 135–139. [9] C. Liu, X. Liu, S. Feng, K.M.U. Rehman, M. Li, C. Zhang, H. Li, X. Meng, Microstructure and magnetic properties of M-type strontium hexagonal ferrites with Y-Co substitution, J. Magn. Magn. Mater. 436 (2017) 126–129. [10] K. Kamishima, T. Goto, H. Nakagawa, N. Miura, M. Ohashi, N. Mori, T. Sasaki, T. Kanomata, Giant magnetoresistance in the intermetallic compound Mn3GaC, Phys. Rev. B. 63 (2000) 024426. [11] R. Huang, L. Li, F. Cai, X. Xu, L. Qian, Low-temperature negative thermal expansion of the antiperovskite manganese nitride Mn3CuN codoped with Ge and Si, Appl. Phys. Lett. 93 (2008) 081902. [12] Y. Sun, C. Wang, Y. Wen, L. Chu, M. Nie, F. Liu, Negative thermal expansion and correlated magnetic and electrical properties of Si-doped Mn3GaN compounds, J. Am. Ceram. Soc. 93 (2010) 650–653. [13] S. Chaudhury, S.K. Rakshit, S.C. Parida, Z. Singh, K.D.S. Mudher, Studies on structural and thermo-chemical behavior of MFe12O19(s) (M=Sr, Ba and Pb) prepared by citrate-nitrate gel combustion method, J. Alloys Compd. 455 (2008) 25–30. [14] X.B. Chen, N.T.M. Hien, K. Han, J.C. Sur, N.H. Sung, B.K. Cho, I.S. Yang, Raman
[25]
[26] [27] [28] [29] [30]
[31]
[32] [33]
[34]
[35] [36]
[37] [38]
[39]
8
studies of spin-phonon coupling in hexagonal BaFe12O19, J. Appl. Phys. 114 (2013) 013912. S. Bierlich, T. Reimann, H. Bartsch, J. Töpfer, Co/Ti-substituted M-type hexagonal ferrites for high-frequency multilayer inductors, J. Magn. Magn. Mater. 384 (2015) 1–5. H. Kuwahara, Y. Tomioka, A. Asamitsu, Y. Moritomo, Y. Tokura, A First-Order Phase Transition Induced by a Magnetic Field, Science. 270 (1995) 961–963. T. Sarkar, V. Pralong, V. Caignaert, B. Raveau, Competition between ferrimagnetism and magnetic frustration in zinc substituted YBaFe4O7, Chem. Mat. 22 (2010) 2885–2891. A.K. Nayak, R. Sahoo, C.S. Mejia, M. Nicklas, C. Felser, Magnetic phase coexistence and metastability caused by the first-order magnetic phase transition in the Heusler compound Mn2PtGa, J. Appl. Phys. 117 (2015) 17D715. K. Sinha, H. Wang, X. Wang, L. Zhou, Y. Yin, W. Wang, X. Cheng, D.J. Keavney, H. Cao, Y. Liu, X. Wu, X. Xu, Tuning the neel temperature of hexagonal ferrites by structural distortion, Phys. Rev. Lett. 121 (2018) 237203. A.M. Alsmadi, I. Bsoul, S.H. Mahmood, G. Alnawashi, F.M. Al-Dweri, Y. Maswadeh, U. Welp, Magnetic study of M-type Ru-Ti doped strontium hexaferrite nanocrystalline particles, J. Alloys Compd. 648 (2015) 419–427. P. Gaunt, Domain wall pinning at random inhomogeneities, IEEE Trans. Magn. 5 (1983) 2030. A.M. Alsmadi, I. Bsoul, S.H. Mahmood, G. Alnawashi, K. Prokeš, K. Siemensmeyer, B. Klemke, H. Nakotte, Magnetic study of M-type doped barium hexaferrite nanocrystalline particles, J. Appl. Phys. 114 (2013) 243910. L. Morellon, P. Algarabel, M. Ibarra, J. Blasco, B.G. Landa, Z. Arnold, F. Albertini, Magnetic-field-induced structural phase transition in Gd5(Si1.8Ge2.2), Phys. Rev. B. 58 (1998) R14721. I.S. Lyubutin, C.R. Lin, S.S. Starchikov, A.O. Baskakov, N.E. Gervits, K.O. Funtov, Y.T. Tseng, W.J. Lee, K.Y. Shih, J.S. Lee, Structural, magnetic, and electronic properties of mixed spinel NiFe2-xCrxO4 nanoparticles synthesized by chemical combustion, Inorg. Chem. 56 (2017) 12469–12475. G. Vértesy, I. Tomáš, Z. Vértesy, On the temperature dependence of domain wall pinning field in soft, uniaxial magnetic materials, J. Phys. D: Appl. Phys. 35 (2002) 625–630. A. Falcón-Cortés, D. Boyer, L. Giuggioli, S.N. Majumdar, Localization transition induced by learning in random searches, Phys. Rev. Lett. 119 (2017) 140603. L. Zhang, L.S. Ling, J.Y. Fan, R.W. Li, S. Tan, Y.H. Zhang, 3D-Heisenberg ferromagnetic characteristics in CuCr2Se4, J. Appl. Phys. 109 (2011) 113911. L. Levy, Magnetism and Superconductivity, Springer, Berlin, 2000. B.K. Banerjee, On a generalized approach to first and second order magnetic transitions, Phys. Rev. Lett. 12 (1964) 16–17. P. Zhang, P. Lampen, T.L. Phan, S.C. Yu, T.D. Thanh, N.H. Dan, V.D. Lam, H. Srikanth, M.H. Phan, Influence of magnetic field on critical behavior near a first order transition in optimally doped manganites: The case of La1-xCaxMnO3 (0.2 ≤ x ≤ 0.4), J. Magn. Magn. Mater. 348 (2013) 146–153. C. Yang, B.Y. Qu, S.S. Pan, L. Zhang, R.R. Zhang, P. Tong, R.C. Xiao, J.C. Lin, X.G. Guo, K. Zhang, H.Y. Tong, W.J. Lu, Y. Wu, S. Lin, W.H. Song, Y.P. Sun, Large positive thermal expansion and small band gap in double-ReO3-type compound NaSbF6, Inorg. Chem. 56 (2017) 4990–4995. H. Sowa, Pressure-induced Fm-3m R-3 phase transition in NaSbF6, Acta Cryst. B. 53 (1997) 25–31. A.M. Abakumov, M. Batuk, A.A. Tsirlin, O.A. Tyablikov, D.V. Sheptyakov, D.S. Filimonov, K.V. Pokholok, V.S. Zhidal, M.G. Rozova, E.V. Antipov, J. Hadermann, G.V. Tendeloo, Structural and magnetic phase transitions in the AnBnO3n-2 anion-deficient perovskites Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16, Inorg. Chem. 52 (2013) 7834–7843. M. Stoia, C. Pǎcurariu, C. Mihali, I. Mǎlǎescu, C.N. Marin, A. Cǎpraru, Manganese ferrite-polyaniline hybrid materials: electrical and magnetic properties, Ceram. Int. 45 (2019) 2725–2735. C. Bonati, M. D’Elia, E. Vicari, Universal scaling effects of a temperature gradient at first-order transitions, Phys. Rev. B. 89 (2014) 062132. H.M. Fan, J.B. Yi, Y. Yang, K.W. Kho, H.R. Tan, Z.X. Shen, J. Ding, X.W. Sun, M.C. Olivo, Y.P. Feng, Single-crystalline MFe2O4 nanotubes/nanorings synthesized by thermal transformation process for biological applications, ACS Nano 3 (2009) 2798–2808. R. Nepal, Q. Zhang, S. Dai, W. Tian, S.E. Nagler, R. Jin, Structural and magnetic transitions in spinel FeMn2O4 single crystals, Phys. Rev. B. 97 (2018) 024410. D. Carta, M.F. Casula, A. Falqui, D. Loche, G. Mountjoy, C. Sangregorio, A. Corrias, A structural and magnetic investigation of the inversion degree in ferrite nanocrystals MFe2O4 (M=Mn Co, Ni), J. Phys. Chem. C. 113 (2009) 8606–8615. L. Hu, J. Chen, A. Sanson, H. Wu, C.G. Rodriguez, L. Olivi, Y. Ren, L. Fan, J. Deng, X. Xing, New insights into the negative thermal expansion: direct experimental evidence for the “guitar-string” effect in cubic ScF3, J. Am. Chem. Soc. 138 (2016) 8320–8323.
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Research articles
First-order magnetic transition induced by structural transition in hexagonal structure ⁎
T
⁎
Chaocheng Liua, Xucai Kana, , Xiansong Liua, , Shuangjiu Fenga, Jiyu Hua, Wei Wanga, Khalid Mehmood Ur Rehmana, Mudssir Shezada, Lei Zhangb a b
Engineering Technology Research Center of Magnetic Materials, School of Physics & Materials Science, Anhui University, Hefei 230601, People’s Republic of China High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China
A R T I C LE I N FO
A B S T R A C T
Keywords: M-type hexaferrites Structural transition First-order AFM transition Thermal hysteresis
Herein, A first-order antiferromagnetic (AFM) phase transition is observed in SrFe12O19 hexaferrites, the detailed analysis has been investigated systematically by magnetic measurements and confirmed it depend on magnetic field. Interestingly, the original peak appear in variable temperature X-ray diffractions, and structural transition change from space group P63/mmc to P-62c around critical temperature without destroying hexagonal crystal system, which is illustrated to be the driving force to result in first-order AFM transition. Furthermore, An apparent phenomenon of magnetic phase transition exhibits in M(H) curves, some characteristic properties of critical temperature and field are specifically correspond to the one of thermal hysteresis and structural transition, suggesting the strong coupling between structural and magnetic transition.
1. Introduction Magnetoplumbite-type hexaferrites compounds with a formula MFe12O19 (M = Ba, Sr, Pb, Ca, etc.) have been studied extensively due to the significative properties they exhibited, such as magnetocaloric effect (MCE) [1], magnetostriction (MS) effect [2], giant magnetoresistance (GMR) effect [3], microwave absorption effect, high maximum energy product and large uniaxial magnetocrystalline [4]. Besides, Mtype strontium hexagonal ferrites always maintain a significant research topic in materials sciences, and also are useful in permanent magnets, magnetic storage media, electromagnetic wave absorbers, high-frequency devices and absorbers of the EMR [5]. In this compounds, Sr, Fe and O ions formed two kinds of close-packed blocks (S blocks and R blocks), the crystal structure of MFe12O19 belongs to closepacked hexagonal packing structure, which are composed of S and R blocks along the hexagonal c-axis according to an order sequence of spinel block (S = Fe6O82+) and hexagonal block (R = MFe6O112−) [6]. There are two oxygen ion layers in spinel block while hexagonal block possess three, and these five oxygen ion layers make up all three different interstice (tetrahedral interstice, bipyramidal interstice and octahedral interstice) [7]. Among that, all five Fe3+ ions are distributed in these three interstitial orbits formed by oxygen ions in each unit cell, they are 4f1 (tetrahedral site), 2b (bipyramidal site), 2a, 12k and 4f2 (octahedral site), where the magnetic moment of Fe3+ ions in 2a, 2b
⁎
and 12 k sites are spin up, yet 4f1 and 4f2 sites hold the magnetic moment spin down [8]. The upward magnetic moments have a positive effect on magnetization, while the downward one will lead to a decrease in magnetization, and the Fe3+ in different interstitial orbits can achieve superexchange interaction through oxygen atom (Fe3+–O–Fe3+), which are determined to be the major origin of magnetism [9]. Not hard to find that once crystal structure of MFe12O19 transformed, it will certainly result in some changes in magnetism to some extent based on the analysis of the magnetoplumbite-type hexaferrites structure above. For this purpose, it is worthwhile and interesting to investigate the connections between structural phase transition and magnetic phase transition. Recently, the investigation of structural phase transition has been proved to be the hotspot for theoretical research, attracted more and more attention and recognition as well. In general, structural transformation usually occurs in relatively simple crystalline systems with high symmetry, such as cubic system. One such typical case is the ternary intermetallic compounds AXM3 (A = Ga, Al, Sn, Zn, Cu, In, Ge, etc.; X = C, N; M = Mn, Fe, Co, Ni, etc.), which subordinate to antiperovskite structure [10–12]. In these intermetallic compounds, structural phase transition can be observed frequently and magnetic phase transition is most often occurred induced by it. However, for M-type hexaferrites, the phenomenon of structural phase transition cannot be observed easily, let alone the appearance of magnetic phase transition.
Corresponding authors. E-mail addresses: [email protected] (X. Kan), [email protected] (X. Liu).
https://doi.org/10.1016/j.jmmm.2019.165821 Received 12 August 2019; Received in revised form 5 September 2019; Accepted 9 September 2019 Available online 11 September 2019 0304-8853/ © 2019 Elsevier B.V. All rights reserved.
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Certainly, the occurrence of the sharp peak also can be associated with the effect of the magnetic domain wall motion according to the literature [20]. For ZFC curve, the magnetic domain are blocked randomly in zero applied field along the oriented easy directions, and the net magnetization will be established due to the 180° domain wall flip toward to the direction of the applied field. Even so, there are still some domain walls pinned owing to the complicated microstructure in the system, and can be unpinned through thermal activation [21]. Under this circumstance, executing the measurement process with increasing temperature will cause two phenomenon occur in the curve: One is the usual drop in magnetization (Ms) because of the thermal agitation, and another is the little increase in Ms due to the unpinning of the domain walls and flip into the direction of the applied field as increasing temperature [22]. According to the literature reported by A.M. Alsmadi [22], the effect of competition between domain wall unpinning (i.e. easy domain wall motion) and thermal agitation of spins will lead to a peak in ZFC curve, while an apparent sharp peak in this work is much higher than that one. Therefore, we prefer the theory of magnetic phase transition, and subsequently verify this result by other relevant measurements and elaboration. The separation of FCC and FCW branches of M(T) shows the occurrence of thermal hysteresis within this temperature region, indicating the potential characteristics of magnetic phase transition according to the literature report [16,23]. Fig. 1(b) gives the FCC and FCW curves with the magnetic field of 0.1 kOe, 1 kOe and 10 kOe. As shown, an apparent division appear in magnetic field of 0.1 kOe, the longitudinal span between FCC and FCW branches of M(T) is narrowed significantly at 1 kOe and coincide completely as the magnetic field up to 10 kOe. For the further study on the magnetic field dependent thermal hysteresis, Fig. 1(c) shows the FCC and FCW curves with more detailed magnetic field range from 1.5 kOe to 8 kOe. Apparently, this two branches overlap basically starting with a magnetic field of 1.5 kOe and until they coincide completely under higher magnetic field. That means thermal hysteresis disappear almost as the magnetic field reaches 1.5 kOe, we argue that this magnetic field is the critical field to start to achieve the constraint of antiferromagnetic effect and ferromagnetic effect recovery the dominance gradually in the following illustration [24]. In addition, the sign of thermal hysteresis vanish gradually as we change the magnetic field strongly, this explains the possible AFM-FM phase transition depends not only on temperature but also on magnetic field. To better understand the nature of magnetic phase transition in the sample, Fig. 2(a) gives initial M-H curves to explain magnetization dynamics. All initial isothermal magnetization display the complete dynamic magnetization process at the interval of 5 K. A distinct mutation region occurs in the curve around the 2000 Oe − 5000 Oe range, this may be caused by the AFM-FM transition based on the above analysis. Meanwhile, the hypothesis cannot be ruled out the possibility due to the growth of magnetization as a result of domain wall motion and domain rotation in a system having domain wall pinning [25]. Fig. 2(b) gives the slope for initial M-H curves around the temperature near phase transition. As shown, we choose the slope region through the whole phase transition field (around 1000 Oe – 10,000Oe) as nine parts to linear fitting. And the slope can be expressed as:
This circumstance is attributed to the structural type, MFe12O19 hexaferrites possess close-packed hexagonal structure (space group P63/ mmc, No. 194) [13,14], and the symmetry of this structure is much lower than that of cubic system. Besides, the magnetocrystalline anisotropy of MFe12O19 belong to uniaxial type, which is different from the planar one for cubic crystal system [15], all these distinctions will lead to the difficulty of structural phase transition in magnetoplumbite-type hexaferrites. Consequently, exploring and investigating the internal coupling between magnetism and structural phase transition of MFe12O19 will be full of novelty and challenge, and some interesting characteristics are expected to appear in MFe12O19. In this paper, we have successfully synthesized SrFe12O19 hexaferrites compounds and found the obvious evidence for first-order phase transition. Detailed researches and investigations of phase transition for SrFe12O19 indicated that varying temperature result in structural transition, and it further triggered the appearance of magnetic transition. The phenomenon of thermal hysteresis obviously exists in field-cooled cooling (FCC) and field-cooled warming (FCW) processes, illustrating the occurrence of first-order magnetic transition in SrFe12O19 hexaferrites [16]. Meanwhile, a first-order antiferromagnetic (AFM) phase transition induced by structural transition is confirmed in SrFe12O19, the competition between antiferromagnetic-ferromagnetic (AFM-FM) is observed and the dominant effect of AFM reaches strongest around 323 K (TN) [17]. It is also worth mentioning that magnetic phase transition begins to occur around 270 K in the process of variable temperature magnetic measurement, which is basically consistent with the onset temperature of thermal hysteresis. 2. Experimental details Polycrystalline sample of SrFe12O19 hexaferrites powders were synthesized by the conventional ceramic method. SrCO3 (Aladdin) and Fe2O3 (Aladdin) raw materials were weighted according to stoichiometric ratio and mixed in planetary mill (Pulverisette; Fritsh GmbH, Germany). The whole mixing process lasts for 3 h with an angular velocity of 300 revolutions per minute, then take out the mixture slurry and dry it. Finally, presintering the prepared sample at 1523 K for 2 h and good-quality sample could be obtained. The information of phase compositions and structure were detected by variable temperature Xray diffraction (Rigaku-TTR3) with Cu Kα radiation from 300 K to 500 K. The Rietveld refinement of XRD data was carried on Rietica software to fit the phase and structure information. The crystal structure diagram were built by Materials Studio and Vesta software. The differential scanning calorimetry (DSC) were performed thermal behavior of the sample. The variable temperature magnetic properties were analyzed by a Quantum Design superconducting quantum interference device magnetic property measurement system (SQUID-MPMS 3) from 250 K to 390 K with applied field 30 kOe. 3. Results and discussion Fig. 1 shows the temperature dependent magnetization M(T) curves for SrFe12O19 hexaferrites compounds. Fig. 1(a) presents the zero-fieldcooled (ZFC), field-cooled cooling (FCC), and field-cooled warming (FCW) processes with the temperature between 200 and 380 K at a magnetic field of 0.1 kOe. Obviously, The ZFC curve undergoes an abnormal sharp raise peak with increasing temperature, which directly demonstrate there are some abnormal magnetic competition in this system [18]. M-type strontium hexaferrites can be described as the compound body of antiferromagnetic and ferromagnetic, it is all due to the truth that SrFe12O19 has both spin-up and spin-down magnetic moments. That is to say, the characteristic of antiferromagnetic (AFM) and ferromagnetic (FM) coexist in the system, Hence, the bulging peak may can be attributed to the result of competition between antiferromagnetic and ferromagnetic (AFM-FM), and this temperature is defined as the Néel temperature (TN) [19].
K = (M2 − M1)/(H2 − H1) = ΔM /ΔH
(1)
Here, M and H are magnetic parameters in initial M-H curves. According to the concept of second order phase transition [26]: Secondorder phase transition, or “second-order phase transition” or “continuous phase transition”, is mainly due to the fact that the curve of the rate of change of free energy (or other ordered parameters, such as magnetization) to temperature (or other parameters, such as magnetic field), remains continuous and does not change abruptly. Quite evidently, Fig. 2(c) reveals a discontinuous slope curve as the plot change abruptly around the region of magnetic phase transition field. This is 2
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Fig. 1. Temperature dependent magnetization M(T) curves of SrFe12O19 hexaferrites with different magnetic fields (0.1 kOe ≤ H ≤ 10 kOe).
where a and b are temperature-dependent [28]. For the condition of equilibrium (∂G/∂M = 0, i.e., energy minimization), the magnetic equation of state evolves into bellow [27]:
more direct argument to illustrate that this magnetic phase transition ought to be first order phase transition. M2 vs H/M are plotted in Fig. 3. It can be seen clearly that all lines of M2 versus H/M are converged at origin and parallel to each other in high field region. According to the Landau theory of phase transition, the Gibbs free energy G can be expressed by following equation in terms of the order parameter M as [27]:
G (T , M ) = G0 + aM 2 + bM 4 − −MH
H / M = 2a + 4bM 2
(3)
Ordinarily, M2 versus H/M should be a series of straight line paralleled to each other in the high field region. On the Basis of the criterion proposed by Banerjee [29], the slope of straight line in Arrott
(2)
Fig. 2. The initial magnetization curves for SrFe12O19 hexaferrites (the inset part is an enlargement region of phase transition and the variety of linear fitting). 3
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peak can be clearly observed in this enlarged region. The occurrence of original phase in the patterns provides the most direct evidence for the existence of structural phase transition from one phase to another phase with a mixed phase in some intermediate temperature [2,31]. Especially, the new and original characteristic peak appear in the transition from 320 to 330 K, and then disappear in the XRD patterns as temperature exceeds 410 K. This variation tendency is in well agreement with the result of first-order antiferromagnetic (AFM) phase transition, and the temperature of structural phase transition closely correspond to the magnetic transition temperature dominated by antiferromagnetic effect [32]. It is worth mentioning that the shrink of Bragg’s peak also may lead to an appearance of weak sharper peaks, but it is not very suitable for this XRD pattern as an obvious evolution of the intensity peak. From what has been discussed above, a first-order antiferromagnetic (AFM) phase transition and structural phase transition are inevitably related to some extent, that is, structural phase transition leads to the occurrence of magnetic phase transition, and we give the further explanations in the following crystal structure studies to figure out this assertion. In order to study the detailed transformation of crystal structure, we select the diffraction patterns before and after the transition at 300 K and 350 K to perform the Rietveld refinements respectively. As revealed in Fig. 5(a), the Rietveld refinement of room-temperature XRD pattern accepts a close-packed hexagonal packing structure (space group: P63/ mmc), while Fig. 5(c) exhibits the pattern of SrFe12O19 hexaferrites with the space group: P-62c at 350 K. Apparently, varying temperature lead to the phase transition in crystal structure, space group change from P63/mmc to P-62c. In addition, Fig. 5(b) and Fig. 5(d) display the sketch diagram of the crystal structure at 300 and 350 K separately. Clearly, there are some specific O atoms changed in lattice sites and occupy different positions compared 300 with 350 K in the crystal structure. Undoubtedly, changed O atoms will cause the variation of interval space type and occupancy of Fe atoms, this behavior theoretically becomes the essential and original factor that does render the magnetic phase transition possible [33]. Fig. 6 shows the detailed interval types and atomic occupancy for SrFe12O19 from top and bottom perspectives at 300 and 350 K. As clearly depicted, The O atoms occupy the convergence of three octahedral interstice viewed from the top and bottom at 300 K, but occupy the vertex of tetrahedral interstice at 350 K. This evident change cause
Fig. 3. The Arrott plot: isotherms of M2 versus H/M.
plot can be used to determine the order of the magnetic transition: the positive slope match with the second order transition while the negative slope corresponding to the first order transition. Undoubtedly, the slope of Arrott plot imply second magnetic transition in the sample at high field, while a negative slope in Arrott plot can be detected as semicircular shape at the initial region, it also directly suggest that the magnetic phase transition should be defined as first order transition according to the Banerjee criterion. This determination is in agreement with the analyses of M2 vs H/M reported by P. Zhang et al [30]. Through a series of discussions above, we firmly believe that there is a first order magnetic phase transition in SrFe12O19 hexaferrites. In order to explore the possible motivation of magnetic phase transition, the further analyses for structure phase are minutely depicted. Fig. 4(a) exhibits the temperature dependent X-ray diffraction patterns with the temperature from 300 to 500 K. It is absolutely essential to point out that the XRD pattern at 300 K is standard pure phase for SrFe12O19 hexaferrites. On the whole, all XRD patterns are similar at different temperature, but there are some new phase begin to appear in XRD patterns at 330 K and disappear at 440 K. Fig. 4(b) gives the locally amplified XRD spectra around 2θ = 50° − 52°, and the characteristic
Fig. 4. Variable temperature X-ray diffraction patterns for SrFe12O19 under warming measurement from 300 to 500 K. 4
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Fig. 5. The Rietveld refined X-ray diffractions at 300 and 350 K for SrFe12O19 hexaferrites and corresponding crystal structure respectively.
crystal structure phase transition should be the reason why the firstorder antiferromagnetic (AFM) phase transition exists in SrFe12O19 hexaferrites compounds [2]. Fig. 7 shows the differential scanning calorimetry (DSC) curve of
the transformation of atomic site occupation indeed, and the specific occupancy of atoms in each orbit are listed in Table 1. As known, performance is usually determined by structural characteristics. Accordingly, through the above research work of structure transition, the
Fig. 6. The interstitial structure of top and bottom perspectives for SrFe12O19 hexaferrites at 300 K and 350 K. 5
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Table 1 The atomic occupancy of SrFe12O19 hexaferrites crystal structures under 300 K (out brackets) and 350 K (in brackets). Atom
Sr Fe Fe Fe Fe Fe O O O O O
Wyckoff
2d 2a 4e 4f 4f 12 k 4e 4f 6h 12 k 12 k
300 K:P63/mmc─(350 K:P-62c) x/a
y/b
z/c
Occupancy
0.6667(0.3333) 0(0) 0(0) 0.3333(0.3333) 0.3333(0.3333) 0.1689(0.1689) 0(0) 0.3333(0.3333) 0.1817(0.1817) 0.1565(0.1565) 0.5047(0.5047)
0.3333(0.6667) 0(0) 0(0) 0.6667(0.6667) 0.6667(0.6667) 0.3378(0.3378) 0(0) 0.6667(0.6667) 0.3634(0.3634) 0.3130(0.3130) 1.0094(0.0094)
0.25(0.75) 0(0) 0.2542(0.2458) 0.0272(0.0272) 0.1909(0.1909) −0.1093(0.6093) 0.1516(0.1516) −0.0552(0.5552) 0.25(0.25) 0.0527(0.0527) 0.1508(0.1508)
1(1) 1(1) 0.5(0.5) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1)
Fig. 7. Differential scanning calorimetry (DSC) of SrFe12O19 hexaferrites.
transition from 270 K to 390 K, performed as the shape of outward bulge in the curve, the onset temperature of magnetic phase transition is coincided well with the that of thermal hysteresis [37]. Another significant feature is that all curves of the magnetic phase transition are driven around 1.5 kOe, This critical magnetic field are also well consistent with the one that thermal hysteresis begins to disappear (see Fig. 1). Probably, a first-order antiferromagnetic phase transition start to subside around 1.5 kOe, which means, a larger magnetic field is needed to restrain the orientation of reverse magnetic moment, and force it complete the process of AFM-FM phase transition [24]. This transversion demands for higher magnetic field to make the curves to meet saturation, and shown as an obviously mutation in hysteresis loop diagram [38]. Besides, structural transition may force the change of domains in SrFe12O19 hexaferrites magnetic structure, some easily oriented magnetic moments inside the domains are able to turn over toward to the same direction with low external field [39]. Nevertheless, part of difficult-oriented moments will not be affected by low magnetic field, but by high magnetic field. Only the magnetic field reaches the critical value, can the orientation of tough moments inside the domains be achieved. This divergence in the difficulty of orientation results in the occurrence of magnetic phase transition presented as the shape of outward bulge in hysteresis loops.
SrFe12O19 hexaferrites. It can be seen that the obtained thermoanalytical curve has two exothermic effect peaks at 246 K and 337 K respectively. The continuous downward trend at the beginning of the curve can be attributed to the heating process in a crucible [34]. These two specific exothermic peaks is associated with the magnetic and structure phase transition point of SrFe12O19 hexaferrites. The changed heat flow in DSC plot imply the existence of first order transition, this indeed verify the structure phase transition in SrFe12O19 as an occurrence of evident change in heat [35]. Moreover, it is only possible that the appearance of magnetic phase transition is induced by structure transition due to the coincidence of all temperature and field parameters, and the magnetic phase transition can be surely classified as first-order transition as changed heat flow. Fig. 8 displays the M(H) curves under different temperature in the scope of 250 K to 390 K. On the whole, all branches exhibits the typical characteristics of magnetic hysteresis loop, while a conspicuous bulge appear on the curve within a certain extent of magnetic fields. Since the pinning effect of domain wall motion can be excluded definitely by a systematically analyses above, this irregular inflection occurred in the curves indicates the existence of magnetic phase transition in SrFe12O19 hexaferrites [36]. As the enlarged region shown in the lower right corner of Fig. 8, the curve exhibits the characteristic of magnetic 6
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Fig. 8. Magnetic hysteresis loops for SrFe12O19 hexaferrites under varying temperature process from 250 K to 390 K.
Fig. 9. The magnetic phase diagram of H versus T for SrFe12O19 hexaferrites.
Regardless of magnetic field of temperature, the diagram of H versus T is fitted precisely with the phase transition results of structure and magnetism verified above, which interpreted the precision and reliability of first-order phase transition appeared in SrFe12O19 hexaferrites.
The magnetic phase diagram of SrFe12O19 hexaferrites is constructed in Fig. 9 to show the process of phase transition in detail. As shown, the graph can be divided into three parts: AFM region, AFM transition region and FM region. The critical field and constrained field of different temperature are marked in the diagram to reflect the starting and terminating field of antiferromagnetic dominant effect. The area between critical and constrained field is the AFM transition region, the properties of this part are same as the magnetic field values in Fig. 1, where the thermal hysteresis begins and ends at. The critical temperature of structure phase transition is also labeled in Fig. 9, the space information of structure for SrFe12O19 with different space group around critical temperature are given in the picture as well, detailed sketch map of crystal structure have been listed and discussed above.
4. Conclusions In summary, the synthesis, structure and magnetic properties of hexagonal SrFe12O19 compounds have been investigated systematically. Exhilaratingly, a first-order antiferromagnetic (AFM) transition is observed by the thermal hysteresis between FCC and FCW branches, and this first-order transition rely on magnetic field embodied in M(T) curves obviously. The plot of initial M(H) and M2 versus H/M give a 7
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convinced evidence to certify this result. The characteristic of first order structural transition is verified by variable temperature X-ray diffraction and thermal behavior, and the crystal structure around the phasetransition temperature confirm the existence of structural transition, which is demonstrated should be the driving force to compel the firstorder AFM transition. Additionally, typical magnetic phase transition is performed in M(H) curves around critical field and temperature, and the H versus T is constructed by internal crucial parameters exhibited in variable temperature hysteresis loops. It is necessary to emphasize that the properties of first-order AFM and structural transition are well matched respectively, indicating a strong coupling between structural and magnetic transition.
[15]
[16] [17]
[18]
[19]
[20]
Acknowledgments [21]
This work was supported by the National Natural Science Foundation of China (Nos. 51872004, 51802002), Education Department of Anhui Province (Nos. KJ2013B293, KJ2018A0039). In addition, the authors thank Professor Lei Zhang for his help in the X-ray diffraction measurements.
[22]
[23]
[24]
References [1] K. Shi, Y. Sun, C.V. Colin, L. Wang, J. Yan, S. Deng, H. Lu, W. Zhao, Y. Kazunari, P. Bordet, C. Wang, Investigation of the spin-lattice coupling in Mn3Ga1−xSnxN antiperovskites, Phys. Rev. B. 97 (2018) 054110. [2] L. Zu, S. Lin, Y. Liu, J.C. Lin, B. Yuan, X.C. Kan, P. Tong, W.H. Song, Y.P. Sun, A first-order antiferromagnetic-paramagnetic transition induced by structural transition in GeNCr3, Appl. Phys. Lett. 108 (2016) 031906. [3] S. Lin, H.Y. Lv, J.C. Lin, Y. Huang, L. Zhang, W.H. Song, P. Tong, W.J. Lu, Y.P. Sun, Critical behavior in the itinerant ferromagnet AsNCr3 with tetragonal-antiperovskite structure, Phys. Rev. B. 98 (2018) 014412. [4] Y. Yang, F. Wang, J. Shao, D. Huang, H. He, A.V. Trukhanov, S.V. Trukhanov, Influence of Nd-NbZn co-substitution on structural, spectral and magnetic properties of M-type calcium-strontium hexaferrites Ca0.4Sr0.6-xNdxFe12.0-x(Nb0.5Zn0.5)xO19, J. Alloys Compd. 765 (2018) 616–623. [5] S.V. Trukhanov, A.V. Trukhanov, V.A. Turchenko, A.V. Trukhanov, E.L. Trukhanova, D.I. Tishkevich, V.M. Ivanov, T.I. Zubar, M. Salem, V.G. Kostishyn, L.V. Panina, D.A. Vinnik, S.A. Gudkova, Polarization origin and iron positions in indium doped barium hexaferrites, Ceram. Int. 44 (2018) 290–300. [6] C. Liu, X. Liu, S. Feng, K.M.U. Rehman, M. Li, C. Zhang, H. Li, X. Meng, Effect of YLa-Co substitution on microstructure and magnetic properties of M-type strontium hexagonal ferrites prepared by ceramic method, J. Magn. Magn. Mater. 445 (2018) 1–5. [7] J. Kreisel, H. Vincent, F. Tasset, M. Pate, J. Ganne, An investigation of the magnetic anisotropy change in BaFe12−2xTixCoxO19 single crystals, J. Magn. Magn. Mater. 224 (2001) 17–29. [8] L. Lechevallier, J.L. Breton, J. Teillet, A. Morel, F. Kools, P. Tenaud, Mössbauer investigation of Sr1−xLaxFe12−yCoyO19 ferrites, Phys. B Condens. Matter. 327 (2003) 135–139. [9] C. Liu, X. Liu, S. Feng, K.M.U. Rehman, M. Li, C. Zhang, H. Li, X. Meng, Microstructure and magnetic properties of M-type strontium hexagonal ferrites with Y-Co substitution, J. Magn. Magn. Mater. 436 (2017) 126–129. [10] K. Kamishima, T. Goto, H. Nakagawa, N. Miura, M. Ohashi, N. Mori, T. Sasaki, T. Kanomata, Giant magnetoresistance in the intermetallic compound Mn3GaC, Phys. Rev. B. 63 (2000) 024426. [11] R. Huang, L. Li, F. Cai, X. Xu, L. Qian, Low-temperature negative thermal expansion of the antiperovskite manganese nitride Mn3CuN codoped with Ge and Si, Appl. Phys. Lett. 93 (2008) 081902. [12] Y. Sun, C. Wang, Y. Wen, L. Chu, M. Nie, F. Liu, Negative thermal expansion and correlated magnetic and electrical properties of Si-doped Mn3GaN compounds, J. Am. Ceram. Soc. 93 (2010) 650–653. [13] S. Chaudhury, S.K. Rakshit, S.C. Parida, Z. Singh, K.D.S. Mudher, Studies on structural and thermo-chemical behavior of MFe12O19(s) (M=Sr, Ba and Pb) prepared by citrate-nitrate gel combustion method, J. Alloys Compd. 455 (2008) 25–30. [14] X.B. Chen, N.T.M. Hien, K. Han, J.C. Sur, N.H. Sung, B.K. Cho, I.S. Yang, Raman
[25]
[26] [27] [28] [29] [30]
[31]
[32] [33]
[34]
[35] [36]
[37] [38]
[39]
8
studies of spin-phonon coupling in hexagonal BaFe12O19, J. Appl. Phys. 114 (2013) 013912. S. Bierlich, T. Reimann, H. Bartsch, J. Töpfer, Co/Ti-substituted M-type hexagonal ferrites for high-frequency multilayer inductors, J. Magn. Magn. Mater. 384 (2015) 1–5. H. Kuwahara, Y. Tomioka, A. Asamitsu, Y. Moritomo, Y. Tokura, A First-Order Phase Transition Induced by a Magnetic Field, Science. 270 (1995) 961–963. T. Sarkar, V. Pralong, V. Caignaert, B. Raveau, Competition between ferrimagnetism and magnetic frustration in zinc substituted YBaFe4O7, Chem. Mat. 22 (2010) 2885–2891. A.K. Nayak, R. Sahoo, C.S. Mejia, M. Nicklas, C. Felser, Magnetic phase coexistence and metastability caused by the first-order magnetic phase transition in the Heusler compound Mn2PtGa, J. Appl. Phys. 117 (2015) 17D715. K. Sinha, H. Wang, X. Wang, L. Zhou, Y. Yin, W. Wang, X. Cheng, D.J. Keavney, H. Cao, Y. Liu, X. Wu, X. Xu, Tuning the neel temperature of hexagonal ferrites by structural distortion, Phys. Rev. Lett. 121 (2018) 237203. A.M. Alsmadi, I. Bsoul, S.H. Mahmood, G. Alnawashi, F.M. Al-Dweri, Y. Maswadeh, U. Welp, Magnetic study of M-type Ru-Ti doped strontium hexaferrite nanocrystalline particles, J. Alloys Compd. 648 (2015) 419–427. P. Gaunt, Domain wall pinning at random inhomogeneities, IEEE Trans. Magn. 5 (1983) 2030. A.M. Alsmadi, I. Bsoul, S.H. Mahmood, G. Alnawashi, K. Prokeš, K. Siemensmeyer, B. Klemke, H. Nakotte, Magnetic study of M-type doped barium hexaferrite nanocrystalline particles, J. Appl. Phys. 114 (2013) 243910. L. Morellon, P. Algarabel, M. Ibarra, J. Blasco, B.G. Landa, Z. Arnold, F. Albertini, Magnetic-field-induced structural phase transition in Gd5(Si1.8Ge2.2), Phys. Rev. B. 58 (1998) R14721. I.S. Lyubutin, C.R. Lin, S.S. Starchikov, A.O. Baskakov, N.E. Gervits, K.O. Funtov, Y.T. Tseng, W.J. Lee, K.Y. Shih, J.S. Lee, Structural, magnetic, and electronic properties of mixed spinel NiFe2-xCrxO4 nanoparticles synthesized by chemical combustion, Inorg. Chem. 56 (2017) 12469–12475. G. Vértesy, I. Tomáš, Z. Vértesy, On the temperature dependence of domain wall pinning field in soft, uniaxial magnetic materials, J. Phys. D: Appl. Phys. 35 (2002) 625–630. A. Falcón-Cortés, D. Boyer, L. Giuggioli, S.N. Majumdar, Localization transition induced by learning in random searches, Phys. Rev. Lett. 119 (2017) 140603. L. Zhang, L.S. Ling, J.Y. Fan, R.W. Li, S. Tan, Y.H. Zhang, 3D-Heisenberg ferromagnetic characteristics in CuCr2Se4, J. Appl. Phys. 109 (2011) 113911. L. Levy, Magnetism and Superconductivity, Springer, Berlin, 2000. B.K. Banerjee, On a generalized approach to first and second order magnetic transitions, Phys. Rev. Lett. 12 (1964) 16–17. P. Zhang, P. Lampen, T.L. Phan, S.C. Yu, T.D. Thanh, N.H. Dan, V.D. Lam, H. Srikanth, M.H. Phan, Influence of magnetic field on critical behavior near a first order transition in optimally doped manganites: The case of La1-xCaxMnO3 (0.2 ≤ x ≤ 0.4), J. Magn. Magn. Mater. 348 (2013) 146–153. C. Yang, B.Y. Qu, S.S. Pan, L. Zhang, R.R. Zhang, P. Tong, R.C. Xiao, J.C. Lin, X.G. Guo, K. Zhang, H.Y. Tong, W.J. Lu, Y. Wu, S. Lin, W.H. Song, Y.P. Sun, Large positive thermal expansion and small band gap in double-ReO3-type compound NaSbF6, Inorg. Chem. 56 (2017) 4990–4995. H. Sowa, Pressure-induced Fm-3m R-3 phase transition in NaSbF6, Acta Cryst. B. 53 (1997) 25–31. A.M. Abakumov, M. Batuk, A.A. Tsirlin, O.A. Tyablikov, D.V. Sheptyakov, D.S. Filimonov, K.V. Pokholok, V.S. Zhidal, M.G. Rozova, E.V. Antipov, J. Hadermann, G.V. Tendeloo, Structural and magnetic phase transitions in the AnBnO3n-2 anion-deficient perovskites Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16, Inorg. Chem. 52 (2013) 7834–7843. M. Stoia, C. Pǎcurariu, C. Mihali, I. Mǎlǎescu, C.N. Marin, A. Cǎpraru, Manganese ferrite-polyaniline hybrid materials: electrical and magnetic properties, Ceram. Int. 45 (2019) 2725–2735. C. Bonati, M. D’Elia, E. Vicari, Universal scaling effects of a temperature gradient at first-order transitions, Phys. Rev. B. 89 (2014) 062132. H.M. Fan, J.B. Yi, Y. Yang, K.W. Kho, H.R. Tan, Z.X. Shen, J. Ding, X.W. Sun, M.C. Olivo, Y.P. Feng, Single-crystalline MFe2O4 nanotubes/nanorings synthesized by thermal transformation process for biological applications, ACS Nano 3 (2009) 2798–2808. R. Nepal, Q. Zhang, S. Dai, W. Tian, S.E. Nagler, R. Jin, Structural and magnetic transitions in spinel FeMn2O4 single crystals, Phys. Rev. B. 97 (2018) 024410. D. Carta, M.F. Casula, A. Falqui, D. Loche, G. Mountjoy, C. Sangregorio, A. Corrias, A structural and magnetic investigation of the inversion degree in ferrite nanocrystals MFe2O4 (M=Mn Co, Ni), J. Phys. Chem. C. 113 (2009) 8606–8615. L. Hu, J. Chen, A. Sanson, H. Wu, C.G. Rodriguez, L. Olivi, Y. Ren, L. Fan, J. Deng, X. Xing, New insights into the negative thermal expansion: direct experimental evidence for the “guitar-string” effect in cubic ScF3, J. Am. Chem. Soc. 138 (2016) 8320–8323.