Journal of Alloys and Compounds 667 (2016) 130e133
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Study of the magnetic phase transitions and magnetocaloric effect in Dy2Cu2In compound Yikun Zhang a, b, c, d, *, Xiao Xu a, b, c, Yang Yang a, b, c, Long Hou a, b, c, Zhongming Ren a, b, c, Xi Li a, b, c, *, Gerhard Wilde d a
State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai, 200072, China Shanghai Key Laboratory of Advanced Ferrometallurgy, Shanghai University, Shanghai, 200072, China School of Materials Science and Engineering, Shanghai University, 200072, China d Institute of Materials Physics, University of Münster, Wilhelm-Klemm-Straße 10, D-48149, Münster, Germany b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 December 2015 Received in revised form 19 January 2016 Accepted 21 January 2016 Available online 22 January 2016
The magnetic properties and magnetocaloric effect (MCE) in Dy2Cu2In compound have been investigated. Dy2Cu2In undergoes two magnetic phase transitions, a paramagnetic to ferromagnetic (FM) at TC ~ 49.5 K followed by a spin reorientation (SR) at TSR ~ 19.5 K. For a magnetic field change of 0e7 T, the maximum values of the magnetic entropy change (DSmax M ) are estimated to be 16.5 around TC and 6.7 J/ kg K around TSR with a large relative cooling power (RCP) value of 617 J/kg. The modified Arrott plots and universal curves of the rescaled DSM confirmed that the magnetic phase transitions in Dy2Cu2In compound belongs the second order phase transitions. The present results may provide some clues to search for new magnetocaloric materials belonging to RE2T2X system. © 2016 Elsevier B.V. All rights reserved.
Keywords: Dy2Cu2In compound Magnetocaloric effect Magnetic phase transitions Magnetic refrigeration
1. Introduction Magnetic refrigeration based on the magnetocaloric effect (MCE) is an energy-effective and environmental friendly cooling technology compared to the conventional gas compression techniques [1e5]. The MCE is an intrinsic thermodynamic phenomenon for magnetic materials, which can be characterized by the adiabatic temperature change (DTad) or/and isothermal magnetic entropy change (DSM) under a varying magnetic field. Normally, materials with the first order phase transition always possess a large sharp DSM peak around their transition temperatures. However, the first order phase transitions are often accompanied by considerable thermal and/or magnetic hysteresis. In contrast, materials with the second order phase transition always present reversible MCE with a broader temperature range which is beneficial for application. In recent years, much attention has been paid to the rare earth based intermetallic compounds with the second order phase transition, and some of
* Corresponding authors. State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai, 200072, China. E-mail addresses:
[email protected] (Y. Zhang),
[email protected] (X. Li). http://dx.doi.org/10.1016/j.jallcom.2016.01.157 0925-8388/© 2016 Elsevier B.V. All rights reserved.
them are found to possess excellent MCE properties that are attractive for active magnetic refrigeration [6e15]. The ternary intermetallic compounds RE2T2X (RE ¼ rare earth, T ¼ transition metal, and X ¼ Mg, Cd, Sn or In) crystallized in the tetragonal Mo2B2Fe-type structure [16] have attracted some attentions because of their interesting properties, especially for the magnetic behaviours. Depending on the constituent element, the RE2T2X compounds undergo various magnetic phase transitions accompanied with a rather wide temperature range of the magnetic transition [17e19]. Among the RE2T2X system, only the crystal structure and some basis magnetic characterization in RE2Cu2In compounds have been reported [20]. To further understand the physical properties of RE2Cu2In compounds, in this paper, the magnetic phase transitions and MCE in Dy2Cu2In were investigated in detail. 2. Experimental High quality polycrystalline sample of Dy2Cu2In was prepared by arc-melting appreciate proportions of constituent with the purity better than 99.9% (at.%) under a titanium-gettered argon atmosphere. The sample was melted four times with the button being turned over after each melting to ensure the homogeneity. The
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obtained arc-melted sample was subsequently annealed at 823 K for 7 days in evacuated quartz tubes. The sample was proved to be single phase by X-ray powder diffraction (XRD). The lattice parameters a and c was evaluated to be 7.466 and 3.746 Å for Dy2Cu2In. The magnetic measurements, including temperature and field dependences of magnetization were performed by using a commercial vibrating sample magnetometer (VSM) which is an option of the physical properties measurement system (PPMS-9, Quantum Design) in the temperature range of 3e300 K, with the DC magnetic fields from 0 to 7 T.
3. Results and discussion Fig. 1 shows the temperature dependence of the zero field cooled (ZFC) and field cooled (FC) magnetization M for Dy2Cu2In under various magnetic fields of H ¼ 0.2, 0.5 and 1 T. The compound undergoes a paramagnetic to ferromagnetic (PM-FM) transition around the Curie temperature of TC ~ 49.5 K which is estimated by evaluating the minimum value of the first-order derivative of the magnetization (dM/dT) as a function of temperature. An additional low temperature magnetic transition at TSR ~19.5 K under low magnetic field and shifting to much lower temperature with increasing magnetic field together with some hysteresis is observed which is probably due to the spin reorientation phenomenon often seen on anisotropy crystalline phase [14,21]. These behaviours are consistent with those of previously reported results [20]. Additionally, the ZFC and FC M-T curves are well overlapped with each other around and above TC, indicating no thermal hysteresis as usually observed in magnetic materials with a second order magnetic phase transition which is beneficial for application. Fig. 2 shows the temperature dependence of the magnetization M (left side) and the reciprocal susceptibility 1/c (right side) for Dy2Cu2In under a high magnetic field of 1 T, respectively. The reciprocal susceptibility 1/c in the PM region obeys the CurieeWeiss law and the paramagnetic Curie temperature qp is evaluated to be 48.0 K that confirms the dominant ferromagnetic interactions in the rare earth sublattice for Dy2Cu2In compound. The paramagnetic Curie temperature qp is deduced from fitting the curve is equal to 10.85 mB, which is close to that of free ion value of Dy3þ (10.63 mB). The magnetic isothermal M(H) for Dy2Cu2In compound is measured in a wide temperature range from 3 to 72 K under applied magnetic field up to 7 T in heating mode, as displayed in Fig. 3(a). It is well known that the magnetic hysteresis during the increasing and decreasing field cycles would lower the cooling power of magnetocaloric materials [22,23]. Therefore, to investigate the
Fig. 1. Temperature dependence zero-field cooling (ZFC) and field cooling (FC) magnetization (M) under the magnetic fields of 0.2, 0.5 and 1 T for Dy2Cu2In compound.
Fig. 2. Temperature dependence of magnetization (M, left scale) and the reciprocal susceptibility (1/c ¼ H/M, right scale) for Dy2Cu2In compound under magnetic field of H ¼ 1 T.
Fig. 3. (a) Magnetic field dependence of the magnetization (increasing field only) for Dy2Cu2In at some selected temperatures. (b) The plots of H/M versus M2 for Dy2Cu2In at some selected temperatures.
magnetic reversibility, the M(H) curves around the TC and TSR are measured increasing and decreasing field. The magnetization increases sharply under low magnetic fields and shows a tendency to saturate with increasing magnetic field. Moreover, each magnetization isotherm around TC shows a completely reversible behaviour during the field increasing and decreasing cycles, which is beneficial to practical applications of magnetic refrigeration materials. The Arrott plot curves of the Dy2Cu2In compound in the temperature range of 3e72 K are shown in Fig. 3(b). As is well known, according to the Banerjee criterion [24], a magnetic transition is expected to be of the first order if some of the H/M versus M2 curves show negative slope at some points. On the other hand, it will be of the second order if slopes of all the H/M versus M2 curves are positive. Only positive slopes can be observed in the Arrott plot curves, indicating magnetic transitions around TC and TSR are of the second order in nature for Dy2Cu2In compound. Fig. 4 shows the temperature dependence of magnetic entropy change DSM for Dy2Cu2In compound for different magnetic field
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Y. Zhang et al. / Journal of Alloys and Compounds 667 (2016) 130e133
Fig. 4. The magnetic entropy change DSM as a function of temperature for various magnetic field changes DН up to 0e7 T for Dy2Cu2In compound. Inset shows the maximum values of magnetic entropy change (DSmax M ) (left-and-up scale), the relative cooling power (RCP) and refrigerant capacity (RC) (right-and-bottom scale) as a function of magnetic field changes for Dy2Cu2In compound.
changes which is calculated from the temperature and field dependence of the magnetization M (H, T) by using an integral version of Maxwell's thermodynamic relation, R Hmax DSM ðT; DHÞ ¼ 0 ðvMðH; TÞ=vT=ÞH dH, in which T is absolute temperature and H is the applied magnetic field. The maximum value of DSM increases monotonically with increasing the magnetic field change. In addition to the pronounced DSM peak at TC, another small DSM peak can be clearly observed around TSR, which is caused by the possible spin reorientation of Dy moments. For the magnetic field changes of 0e2, 0e5, and 0e7 T, the maximum values of the magnetic entropy change (DSmax M ) for Dy2Cu2In are evaluated to be 7.2, 13.3 and 16.5 J/kg K; and to be 1.8, 4.8 and 6.7 J/kg K around TC and TSR, respectively. Recently, Franco et al. have proposed the universal curve for the DSM (T) in compounds with the second order phase transitions [25e27]. The construction of the phenomenological universal curve is based on the rescaled DSM (T) curves for different magnetic field changes by normalizing all the DSM (T) curves with their respective maximum value DSmax (i. e. DS0 ¼ DSM (T)/DSmax M M ) and rescaling the temperature q, given by the expression
q¼
ðT TC Þ=ðTr1 TC Þ; T TC ; ðT TC Þ=ðTr2 TC Þ; T > TC
(1)
where the Tr1 and Tr2 are the temperature of the two reference points of each curve that correspond to xDSmax (x ¼ 0.4e0.7). The M universal curves for present Dy2Cu2In compound are constructed by using x ¼ 0.6. The normalized entropy change DS0 (q) as a function of the rescaled temperature q is shown in Fig. 5. We can note that all curves are overlapped with each other around and above TC, however, the curves show a distinctly difference in the range of 8 < q < 3 (around TSR), which is due to the spin reorientation in the Dy2Cu2In compound. Therefore, the DSM (T) around TSR (7e30 K) is rescaled and the results are shown in the inset of Fig. 5. We can see that the curves around TSR are well overlapped with each other. Furthermore, the rescaled DS0 (q) curves around TC and TSR for Dy2Cu2In compound under various magnetic field changes are summarized together (as given in Fig. 6). All the rescaled DSM curves (including both around TC and TSR) under various magnetic field changes can collapse onto the one universal
Fig. 5. Normalized magnetic entropy change DS0 (¼DSM/DSmax M ) as a function of the rescaled temperature q around TC for Dy2Cu2In compound. Insets shows the normalized magnetic entropy change DS0 (¼DSM/DSmax M ) as a function of the rescaled temperature q around TSR for Dy2Cu2In compound.
Fig. 6. Normalized magnetic entropy change DS0 (¼DSM/DSmax M ) as a function of the rescaled temperature q around TC and TSR for Dy2Cu2In compound.
curve, further confirmed the second order phase transitions in Dy2Cu2In compound. In addition, the relative cooling power (RCP) or/and refrigeration capacity (RC) has also been considered as another criterion to quantify the heat transfer in the thermodynamic cycle. The RCP is defined as the product of the maximum magnetic entropy change DSmax and full width at half maximum dTFWHM in DSM (T) curve, M i.e.RCP ¼ DSmax: dT FWHM . The RC is determined by adopting the RMT2 formulaRC ¼ T1 jDSM jdT, where T1 and T2 are the temperatures of the cold end and the hot end of half maximum of the DSM peak in an ideal thermodynamic cycle, respectively. The RCP and RC as a function of magnetic field changes up to 0e7 T for Dy2Cu2In compound are displayed in the inset (right-and-bottom scale) of Fig. 4. Similar to that of DSmax M , both RCP and RC show continuous increase with increasing the magnetic field change. For the magnetic field changes of 0e2, 0e5 and 0e7 T, the values of RCP and RC are determined to be 133, 409 and 617 J/kg, and to be 101, 318 and 475 J/ kg for Dy2Cu2In, respectively. The transition temperature TM, the maximum values of DSmax M , and the RCP with the field changes of 0e2 and 0e5 T for Dy2Cu2In as well as some MCE materials are listed in Table 1 for comparison. These values for the present Dy2Cu2In compound is comparable even larger than those of some potential magnetic refrigerant materials in the similar temperature region under the same magnetic field changes, indicating that Dy2Cu2In compound could be an alternative candidate material for the low temperature refrigeration application.
Y. Zhang et al. / Journal of Alloys and Compounds 667 (2016) 130e133 Table 1 The transition temperature TC, the maximum values of magnetic entropy change DSmax M and relative cooling power RCP with the field changes of 0e2 T and 0e5 T for Dy2Cu2In compound as well as some MCE materials. Material
TC (K)
Dy2Cu2In ErAgAl HoAgAl HoPdIn DyNiIn EuAuGe NdMn2Ge0.4Si1.6 GdPdAl Pr6Co2Si3 ErFeAl Tb3Ni6Al2
49.5 14 18 23 30 33 36 46 50 55 57
DSmax (J/kg M K)
RCP (J/kg)
2T
5T
2T
5T
7.2 4.2 3.8 7.9 5.5 3.5 12.3 5.6 3.2 2.4 4.8
13.3 10.5 10.3 14.6 10.4 7.6 28.4 10.4 6.1 6.1 9.8
133 73 99 112 e 105 95 200 92 77 130
409 261 344 496 ~354 295 284 422 205 311 389
Ref.
present [28] [28] [14] [29] [30] [31] [32] [33] [34] [35]
A blank column with a mark of “e” means that the value was not reported in the literature.
4. Conclusions In summary, a single phased Dy2Cu2In compound with a tetragonal structure of the Mo2B2Fe-type has been prepared and the magnetic and magnetocaloric properties have been systematically investigated. The Dy2Cu2In undergoes 2 s order magnetic phase transitions at TC ~49.5 K and TSR ~19.5 K, respectively, according to the magnetization measurements and the universal curves of the DSM (T) criterion. For a magnetic field change of 0e5 T, the maximum values of the two magnetic entropy change (DSmax M ) are estimated to be 13.3 and 4.8 J/kg K around TC and TSR, respectively. The corresponding large relative cooling power (RCP) value 409 J/kg with a wide temperature range is obtained. The large reversible DSM and comparable values indicate that the Dy2Cu2In compound could be a good candidate for active magnetic refrigeration in the temperature range of 10e75 K. Acknowledgements The present work was partially supported by the National Natural Science Foundation of China (No. 51501036). Y. K. Zhang acknowledges the Alexander von Humboldt (AvH) Foundation for support with a post-doctoral fellowship.
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