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Microstructural and magnetic properties of Pr–BiCo co-substituted M-type Sr–Ca hexaferrites
Accepted Manuscript
Microstructural and magnetic properties of Pr-BiCo co-substituted M-type Sr-Ca hexaferrites Yujie Yang , Juxiang Shao , Fanhou Wang , Khalid Mehmood Ur Rehman , Jin Tang PII: DOI: Reference:
S0577-9073(17)31501-0 10.1016/j.cjph.2018.02.012 CJPH 458
To appear in:
Chinese Journal of Physics
Received date: Revised date: Accepted date:
21 November 2017 17 February 2018 27 February 2018
Please cite this article as: Yujie Yang , Juxiang Shao , Fanhou Wang , Khalid Mehmood Ur Rehman , Jin Tang , Microstructural and magnetic properties of PrBiCo co-substituted M-type Sr-Ca hexaferrites, Chinese Journal of Physics (2018), doi: 10.1016/j.cjph.2018.02.012
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ACCEPTED MANUSCRIPT Highlights
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 hexaferrites were prepared by standard ceramic method.
The hexaferrite grains have a hexagonal platelet shape with clear grain boundaries. Br first increases and then decreases with increasing Pr-BiCo content (x).
Hcj first decreases and then increases with increasing Pr-BiCo content (x).
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ACCEPTED MANUSCRIPT
Microstructural and magnetic properties of Pr-BiCo co-substituted M-type Sr-Ca hexaferrites Yujie Yang ﹡ 1, Juxiang Shao1, Fanhou Wang1, Khalid Mehmood Ur Rehman2, Jin Tang2 Computational Physics Key Laboratory of Sichuan Province, School of Physics and
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1
Electronic Engineering, Yibin University, Yibin 644007, P. R. China 2
Engineering Technology Research Center of Magnetic Materials, School of Physics
& Materials Science, Anhui University, Hefei 230601, P. R. China
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Abstract
We have synthesized the Pr-BiCo substituted hexaferrites with compositions of Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 (0.0 ≤ x ≤ 0.5) by the standard ceramic method. Results of X-ray diffraction analysis exhibits that the synthesized hexaferrites with x
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from 0.0 to 0.3 are in single magetoplumbite structure, and impurity phases are
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observed when x ≥ 0.4. The surface morphology of magnets shows that hexaferrite grains have a hexagonal platelet shape with clear grain boundaries. The remanence
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first increases with x from 0.0 to 0.1, and then decreases when x ≥ 0.1. The intrinsic coercivity decreases with x from 0.0 to 0.1, and then increases when x ≥ 0.1. With x
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from 0.0 to 0.4, the changing trend of magnetic induction coercivity is in agreement
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with that of Hcj, while at x ≥ 0.4, Hcb decreases. The maximum energy product initially increases with x from 0.0 to 0.2, and then decreases when x ≥ 0.2. Keywords: M-type hexaferrites; Pr-BiCo co-substitution; X-ray diffraction; Magnetic properties 1. Introduction ﹡
Corresponding author. Tel: +86 831 3531171, Fax: +86 831 3531161. E-mail address: [email protected] (Y.J. Yang). 2
ACCEPTED MANUSCRIPT M-type hexaferrites are the most utilized permanent materials due to their low price, moderate energy product, strong uniaxial anisotropy, and high Curie temperature [1]. The magnetic properties of M-type hexaferrites depend on the preparation conditions and the ion site occupation of the substituted ions. There are five different Fe3+ sublattices, such as one tetrahedral (4f1), one bipyramidal (2b) and
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three octahedral (2a, 12k and 4f2) [2]. In this respect, M-type hexaferrites have been the focus of many studies in order to improve their magnetic properties.
It is an effective method to modify the magnetic properties of M-type hexaferrites by the ion substitution. Many studied have been done on the M-type
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hexaferrites with partial substitutions of Sr2+ or Ba2+ ions and Fe3+ ions by several ions, such as La3+ [3], Pr3+ [4], Ce3+ [5], Nd3+ [6], Sm3+ [7], Gd3+ [8], Co2+ [9], Bi3+ [10], Al3+ [11], Cu2+ [12], and Zn2+ [13]. Wang et al. have prepared the Pr doped M-type
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strontium hexaferrite by hydrothermal synthesis and subsequent calculations and found that Pr substitution can increase the coercivity without leading to any distinct
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change in the magnetization [4]. Ezhil Vizhi et al. have synthesized the Co doped
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Ba-Sr hexaferrite Ba0.5Sr0.5Fe12-xCoxO19 (x = 0.0, 0.5, 0.7 and 0.9) by one-step citrate gel combustion method followed by annealing and found that the saturation
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magnetization (Ms) reaches to the maximum value at x = 0.5 [9]. Auwal et al. have reported that for the Bi3+ ions substituted M-type strontium hexaferrite SrBixFe12-xO19
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(0.0 ≤ x ≤ 1.0) synthesized using a co-precipitation assisted ceramic route, and a systemic change in the lattice parameters (a and c) was detected and the results of cation distribution exhibited that Fe3+ ions are distributed uniformly over the tetraand octahedral positions of spinel structure [10]. Many studied have been done on the M-type hexaferrites with combined substitution, such as La-Co [14], La-Zn [15], La-Ni [16], Nd-Co [17], Gd-Co [18], Ce-Co [19], Gd-Sn [20], Pr-Ni [21], Bi-Cr [22],
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ACCEPTED MANUSCRIPT Co-Zr [23], Co-W [24], and Mn-Zn [25]. Shen et al. have studied the La-Ni substituted M-type barium hexaferrites Ba1-xLaxFe12-xNixO19 (0.0 ≤ x ≤ 0.2) produced by the chemical co-precipitation method and found that the magnetoplumbite structure for all the samples have been formed, and Ms and Hc decrease with the increase of substitution content from 0.0 to 0.4 [16]. Iqbal et al. have synthesized the
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Pr-Ni doped M-type hexaferrites Sr0.5Ba0.5-xPrxFe12-yNiyO19 (0.00 ≤ x ≤ 0.10, 0.00 ≤ y ≤ 1.00) by the chemical co-precipitation method and found that the values of Ms and Mr increase with the substitution of Pr-Ni ions up to x = 0.06 and y = 0.60, and the coercivity shows a significant decrease with the substitution of Pr-Ni ions up to x =
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0.06 and y = 0.60 [21]. Shakoor et al. have synthesized the Bi-Cr substituted M-type strontium hexaferrites SrFe12-2xBixCrxO19 (0.0 ≤ x ≤ 0.8) by the sol-gel method and found that Ms and Mr first increases with the increase of Bi-Cr content from 0.0 to 0.2,
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and then decrease when Bi-Cr content ≥ 0.2; while Hc decreases with increasing Bi-Cr content from 0.0 to 0.2, and then increases when Bi-Cr content ≥ 0.2 [22]. Joshi et al. investigated
the
Co-W
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have
doped
M-type
Ba-Sr
hexaferrites
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Ba0.5Sr0.5CoxWxFe12-2xO19 (0.2 ≤ x ≤ 1.0) prepared by the ceramic method and found that SEM images and hysteresis loops of all samples exhibit multidomain particles,
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the coercivity decreases with Co-W content from 0.2 to 1.0 while Ms and Mr first decrease with Co-W content from 0.2 to 0.8 and then increase in x = 1.0 [24].
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In this paper, the element of Pr3+ is chosen to substitute the Sr2+ ions and the
elements of Bi3+ and Co2+ are chosen to substitute the Fe3+ ions. We have synthesized the Pr-BiCo substituted M-type Ca-Sr hexaferrites by the standard ceramic method. And the impacts of Pr-BiCo content on the microstructural and magnetic properties were carefully investigated. 2. Experimental procedure 4
ACCEPTED MANUSCRIPT The standard ceramic method were used to prepare the M-type Ca-Sr hexaferrites with nominal compositions of Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 (0.0 ≤ x ≤ 0.5). The raw materials used in this study were CaCO3 (99% purity), SrCO3 (99% purity), Pr6O11 (99% purity), Fe2O3 (99% purity), Bi2O3 (99% purity) and CoO (99% purity). They were used as such without further treatment. These raw materials were
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mixed together according to their molecular weight ratios, and were wet-grinded in a ball mill at a rotate speed of 80 rpm for 10 h. And the grinded powders were dried in a drying oven in the air, and then calcined in a muffle furnace at 1240 oC for 2.0 h. The calcined powders were shattered to particles, and were again wet-grinded with
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suitable additives (CaCO3, SrCO3, SiO2, Ca(C6H11O7)2) for 18 h in a ball-mill. After that, the finely grinded slurry was pressed into cylindrical pellets, and the pressed pellets were sintered in a muffle furnace at 1190 oC for 1.5 h in air.
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The phase compositions of the samples were confirmed by X-ray diffraction analysis which was carried out using a powder X-ray diffraction (XRD, Rigaku
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D/max-2550V/PC) Cu Kα (λ = 1.5406 Å) radiation. The 2θ angles were scanned over
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a range between 20o and 80o. The surface morphology of magnets was observed by a field emission scanning electron microscopy (FE-SEM, HITACHI S-4800). The
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magnetic properties of the samples were measured at room temperature by a permanent magnetic measuring system (NIM-2000HF, made by the National Institute
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of Metrology of China). 3. Results and discussion 3.1. Structural analysis Fig. 1 shows the X-ray diffraction patterns of the Pr-BiCo substituted M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnetic powders with Pr-BiCo
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ACCEPTED MANUSCRIPT content (x) from 0.0 to 0.5. The observed XRD peaks were indexed. It is seen that for the M-type hexaferrite magnetic powders with Pr-BiCo content (x) from 0.0 to 0.3, the XRD patterns belong to the M-type strontium hexaferrite (JCPDS card no. 80-1198). For the magnetic powders at Pr-BiCo content (x) ≥ 0.4, PrFeO3 is detected in the structure. For the magnetic powders at Pr-BiCo content (x) = 0.5, PrFeO3 and
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α-Fe2O3 are detected in the structure.
The lattice parameters (c and a) of M-type hexaferrites are calculated by the following equation [26]: 1 4 h 2 hk k 2 l 2 2, 2 d hkl 3 a2 c
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(1)
where dhkl is the d-spacing of the lines in XRD pattern and h, k and l are the Miller indices. The variations of the lattice parameters (c and a) as a function of Pr-BiCo content (x) for the M-type hexaferrites Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 are shown
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in Fig. 2. In the present study, one Pr3+ ion substitutes one Sr2+ ion, and both Bi3+ and
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Co2+ ions substitute two Fe3+ ions. It is seen that the lattice constant a is almost constant (5.8872-5.8902 Å) in the experimental errors with increasing the Pr-BiCo
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content (x), while the lattice constant c first increases with the increase of Pr-BiCo
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content (x) from 0.0 to 0.3, and then decreases when Pr-BiCo content (x) ≥ 0.3. The increase of lattice constant c with the increase of Pr-BiCo content (x) from 0.0 to 0.3
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can be attributed to the difference in the ionic radii (Δr) of the metal ions and the number of ionic substitutions of each species. Substitution of Sr2+ (r = 1.180 Å) by Pr3+ (r = 1.013 Å) makes a negative difference in the ionic radii of Δr = -0.167 Å. The ionic radius of Bi3+ was 1.030 Å and that of Co2+ was 0.745 Å, giving an average value of 0.8875 Å for equiatomic BiCo co-substitution. Thus, substitution of Fe3+ (r = 0.645 Å) by Bi3+-Co2+ (the average value of ionic radii is 0.8875 Å) makes a positive
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ACCEPTED MANUSCRIPT difference in the ionic radii of Δr = +0.2425 Å. In the Pr-BiCo substituted M-type hexaferrites, in order to keep the electroneutrality, some Fe3+ ions (r = 0.645 Å) will change into Fe2+ ions (r = 0.780 Å) at 2a or 4f2 site, this makes a positive difference in the ionic radii of Δr = +0.135 Å. As in the case of Pr-BiCo content (x = 0.2), the total content of both Co2+ and Fe2+ ions is equal to that of Pr3+ ions, and the lattice constant
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c is increased. When Pr-BiCo content (x) ≥ 0.4, PrFeO3 is detected in the structure, and at Pr-BiCo content (x) = 0.5, PrFeO3 and α-Fe2O3 are detected in the structure. The impurity phase peak intensity is increased with increasing Pr-BiCo content (x). Thus, the decrease of lattice constant c when Pr-BiCo content (x) ≥ 0.3 can attributed
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to the below reasons. Firstly, in order to keep the electroneutrality, less Fe3+ ions (r = 0.645 Å) will change into Fe2+ ions (r = 0.780 Å) at 2a or 4f2 site. Secondly, the impurity phases such as PrFeO3 and α-Fe2O3 induce lattice distortion for the
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hexagonal structure.
Fig. 3 shows the change of c/a ratios as a function of Pr-BiCo content (x) for the
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M-type hexaferrites Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19. From Fig. 3, it is observed that c/a ratios of M-type hexaferrites slightly increase with the increase of Pr-BiCo
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content (x) from 0.0 to 0.3, and then decrease when Pr-BiCo content (x) ≥ 0.3. The
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lattice constant ratio c/a can be used to quantify the structure type, and an M-type structure can be assumed if the ratio is lower than 3.98 [27]. The c/a ratios with
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different Pr-BiCo contents are in the range from 3.8976 to 3.9153, confirming the formation of M-type hexagonal structure. The
FE-SEM
micrographs
of
M-type
hexaferrite
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets for compositions of x=0.0, x=0.2, and x=0.4 are shown in Fig. 4. It is clearly seen that the hexaferrite grains have a hexagonal platelet shape with clear grain boundaries. The average grain sizes of the
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ACCEPTED MANUSCRIPT magnets for compositions of x=0.0, x=0.2, and x=0.4 are around 3.0 μm, 3.5 μm, and 4.0 μm, respectively. The average grain size is increased with Pr-BiCo content (x). 3.2. Magnetic properties Fig.
5 shows the
demagnetizing curves
of the M-type hexaferrite
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Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets with the increase of Pr-BiCo content (x) from 0.0 to 0.5. In Fig. 5, the blue lines are the intrinsic demagnetizing curves of the M-type hexaferrite magnets and the red lines are the normal demagnetizing curves of the M-type hexaferrite magnets [28]. The value of the intrinsic coercivity (Hcj) is
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larger than that of magnetic induction coercivity (Hcb). Hk is the value of the reverse magnetic field intensity corresponding to B=0.9 Br on the demagnetizing curves. The squareness ratio (Hk/Hcj), where Hk and Hcj are the knee field and intrinsic coercivity, respectively, is an important factor affecting the value of high anisotropy factor [29].
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The remanence (Br), intrinsic coercivity (Hcj), maximum energy product [(BH)max]
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and Hk/Hcj ratio are extracted from demagnetizing curves, and their values are listed in Table 1.
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The variation of the remanence (Br) as a function of Pr-BiCo content (x) for the
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M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets is shown in Fig. 6. It can be seen from Fig. 6 that the value of Br first increases with the increase of
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Pr-BiCo content (x) from 0.0 to 0.1, and then begins to decrease with the increase of Pr-BiCo content (x) from 0.1 to 0.5. In the M-type hexagonal ferrite, Fe3+ ions occupy five different crystallographic sites: three octahedral sites (12k, 4f2 and 2a), one geometric tetrahedron site (4f1), and one bipyramidal site (2b). The 2a, 2b and 12k sites have upward spin configurations, and the 4f1 and 4f2 sites have downward spin configurations. It is reported that Pr3+ ions substitute for Sr2+ ions [4], and Bi3+ ions substitute for Fe3+ ions in the 4f1, 4f2 [10], and Co2+ ions substitute for Fe3+ ions in the 8
ACCEPTED MANUSCRIPT 4f1, 4f2 and 2b sites [30]. The magnetic moment of Fe3+ ion is 5 μB. The magnetic moment of Co2+ ion is 3.7 μB. In the Pr-BiCo substituted M-type hexaferrites, in order to keep the electroneutrality, some Fe3+ ions will change into Fe2+ ions at 2a or 4f2 site. In this study, the increase of the remanence (Br) with Pr-BiCo content (x) from 0.0 to 0.1 can be ascribed to the following two reasons. Firstly, the non-magnetic Bi3+ ions
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occupy the site having spin of electrons in downward direction, which results in the number of Fe3+ ions having spin in upward direction. This leads to the increase of remanence (Br). Secondly, the occupancy of 4f1 and 4f2 sites by Co2+ ions is positive in inhibiting the offsetting of magnetic moment and leads to the increase of bulk
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magnetic moment. This results in the increase of the remanence (Br). However, when the Pr-BiCo content (x) ≥ 0.1, the decrease in the the remanence (Br) can be due to the below three reasons. Firstly, with the doping of Pr3+ ions instead of Sr2+ ions and Bi3+
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and Co2+ ions for Fe3+ ions, the Fe3+-O-Fe3+ superexchange interaction is weakened. This causes to magnetic collinearity to collapse, and leads to the decrease of
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remanence (Br). Secondly, the substituting of Fe3+ (5 μB) ions in the 2b sites by Bi3+ (0
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μB) and Co2+ (3.7 μB) ions and the change of Fe3+ (5 μB) ions to Fe2+ (4 μB) ions result in the decrease of bulk magnetic moment. This leads to the decrease of remanence
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(Br). Thirdly, in M-type hexaferrites, the impurity phases have almost no contribution to the increase of remanence (Br). When the Pr-BiCo content (x) ≥ 0.4, the appearance
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of impurity phases as shown in Fig. 1 can cause the remanence (Br) to decrease. Fig. 7 shows the variations of the magnetic induction coercivity (Hcb) and
intrinsic coercivity (Hcj) as a function of Pr-BiCo content (x) for the M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. It is seen from Fig. 7 that Hcj decreases with increasing Pr-BiCo content (x) from 0.0 to 0.1, and then increases with increasing Pr-BiCo content (x) from 0.1 to 0.5. According to the Stoner-Wohlfarth
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H c 0.64
2K , Ms
(2)
where K is the magnetocrystalline anisotropy constant and Ms is the saturation
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magnetization. Thus, the decrease of Hcj with Pr-BiCo content (x) from 0.0 to 0.1 can be due to the following two reasons. Firstly, according to the formula (2), the increase of remanence (Br) with Pr-BiCo content (x) from 0.0 to 0.1 results in the decrease of the coercivity. Secondly, the decrease of Hcj should be attributed to the decrease of
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uniaxial anisotropy constant because of the occupancy of the 4f2 and 2b sites by Co2+ ions. However, according to the equation (2), the increase of Hcj can be attributed to the decrease of remanence (Br) with increasing Pr-BiCo content (x) from 0.1 to 0.5 as
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shown in Fig. 6. It is also observed from Fig. 7 that for the magenets with Pr-BiCo content (x) from 0.0 to 0.4, the changing trend of Hcb is in agreement with that of Hcj,
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while for the magenets with Pr-BiCo content (x) ≥ 0.4, Hcb begins to decrease. The change of Hk/Hcj ratio as a function of Pr-BiCo content (x) for the M-type hexaferrite
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Ca0.2Sr0.8-xPrxFe12.0-x(Bi0.5Co0.5)xO19 magnets is exhibited in Fig. 8. The Hk/Hcj ratio
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can indicate the rectangularity of the demagnetizing curves for the magnets [31]. It is observed from Fig. 8 that for the magnets with Pr-BiCo content (x) from 0.0 to 0.3,
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the values of Hk/Hcj ratios are in the ranges between 0.938 and 0.972 and the changing trend of Hk/Hcj ratios is very slight, while for the magnets with Pr-BiCo content (x) ≥ 0.3, the value of Hk/Hcj ratio quickly decreases from 0.957 at x=0.3 to 0.554 at x=0.5. This shows that Pr-BiCo substitution has big influence on the rectangularity of the demagnetizing curves for the Pr-BiCo co-substituted M-type Ca-Sr hexaferrites as shown in Fig. 5. When Pr-BiCo content (x) ≥ 0.3, the quick decrease of Hk/Hcj ratio should be attributed to the presence of impurity phase in the structure as shown in Fig. 10
ACCEPTED MANUSCRIPT 1. The quick decrease of Hk/Hcj ratio at Pr-BiCo content (x) ≥ 0.3 may be the reason that Hcb begins to decrease when Pr-BiCo content (x) ≥ 0.4. Fig. 9 shows the change of the maximum energy product [(BH)max] as a function of Pr-BiCo content (x) for the M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. It is clearly seen that the value of (BH)max initially increases with increasing
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Pr-BiCo content (x) from 0.0 to 0.2, and then begins to decrease when Pr-BiCo content (x) ≥ 0.2. The maximum energy product of the M-type hexaferrites could be estimated by the product between the remanence (Br) and coercivity field.
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4. Conclusions
In the present study, the Pr-BiCo substituted M-type with nominal compositions of Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 (0.0 ≤ x ≤ 0.4) were synthesized by the standard ceramic method. We have carefully investigated the effects of Pr-BiCo
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content on the structural and magnetic properties of the Pr-BiCo substituted M-type
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Ca-Sr hexaferrites. The major findings of this study were listed in the following: 1. X-ray diffraction analysis exhibits that when the Pr-BiCo content (x) increases from
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0.0 to 0.3, the synthesized M-type hexaferrite magnetic powders are in single magetoplumbite structure, and impurity phases are observed when Pr-BiCo content
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(x) ≥ 0.4. It is observed that the lattice constant a is almost constant with increasing
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the Pr-BiCo content (x), while the lattice constant c first increases with Pr-BiCo content (x) from 0.0 to 0.3, and then decreases when Pr-BiCo content (x) ≥ 0.3. The results of FE-SEM morphology exhibit that the hexaferrite grains have a hexagonal platelet shape with clear grain boundaries and the average grain size is increased with the increase of Pr-BiCo content (x). 2. Magnetization properties were measured at room temperature using a permanent magnetic measuring system. Br first increases with Pr-BiCo content (x) from 0.0 to 11
ACCEPTED MANUSCRIPT 0.1, and then decreases when Pr-BiCo content (x) ≥ 0.1. Hcj decreases with increasing Pr-BiCo content (x) from 0.0 to 0.1, and then increases when Pr-BiCo content (x) ≥ 0.1. With the increase of Pr-BiCo content (x) from 0.0 to 0.4, the changing trend of Hcb is in agreement with that of Hcj, while at Pr-BiCo content (x) ≥ 0.4, Hcb begins to decrease. (BH)max initially increases with increasing Pr-BiCo
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content (x) from 0.0 to 0.2, and then begins to decrease when Pr-BiCo content (x) ≥ 0.2. Acknowledgements
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This work was supported by the National Natural Science Foundation of China (Nos. 51472004, 51272003), Scientific Research Fund of SiChuan Provincial Education Department (No. 13ZA0918, No. 14ZA0267 and No. 16ZA0330), the Major Project of Yibin City of China (No. 2012SF034, No. 2016GY025 and No.
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2016 QD002), Scientific Research Key Project of Yibin University (No. 2015QD13)
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and the Open Research Fund of Computational Physics Key Laboratory of Sichuan
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P. Dhruv, M. Ghimiree, J. Alloys Compd. 695 (2017) 909
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[24] R. Joshi, C. Singh, D. Kaur, H. Zaki, S.B. Narang, R. Jotania, S. Mishra, J. Singh,
[25] Y.J. Yang, J.X. Shao, F.H. Wang, X.S. Liu, D.H. Huang, Appl. Phys. A 123 (2017) 309
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[26] R.R. Bhosale, R.S. Barkule, D.R. Shengule, K.M. Jadhav, J. Mater. Sci.: Mater. Electron. 24 (2013) 3101
[27] R.S. Alam, M. Moradi, M. Rostami, H. Nikmanesh, R. Moayedi, Y. Bai, J. Magn.
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Magn. Mater. 381 (2015) 1
[28]. A. Goldman, Modern Ferrite Technology, 2nd, Ed., Springer, Pittsburgh, 2006
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[29]. C.-C. Huang, A.-H. Jiang, Y.-H. Hung, C.-H. Liou, Y.-C. Wang, C.-P. Lee, T.-Y.
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Huang, C.-C. Shaw, M.-F. Kuo, C.-H. Cheng, J. Magn. Magn. Mater. 451 (2018) 288 [30] Y. Liu, M.G.B. Drew, Y. Liu, J. Magn. Magn. Mater. 323 (2011) 945
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[31] Z.M. Wang, Ferrite Production Technology, Chongqing University Press,
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Chongqing, 2013
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Table 1. The remanence (Br), magnetic induction coercivity (Hcb), intrinsic coercivity (Hcj), maximum energy product [(BH)max] and Hk/Hcj ratio for M-type hexaferrites
Table 1
Hcj (kA/m) 148.5 122.9 139.1 185.9 203.4 239.9
(BH)max (kJ/m3) 28.56 29.32 30.21 28.33 19.41 10.20
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Hcb (kA/m) 145.4 118.0 137.5 180.2 194.4 158.8
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Br (mT) 404.1 417.5 405.9 384.4 321.6 236.3
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Pr-BiCo content (x) 0.0 0.1 0.2 0.3 0.4 0.5
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Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 with different Pr-BiCo content (x).
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Hk/Hcj 0.938 0.960 0.972 0.957 0.860 0.554
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Figure captions Fig.
1.
XRD
patterns
of
the
Pr-BiCo
substituted
Fig.
2.
Lattice
parameters
(c
and
a)
hexaferrites
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Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19.
M-type
of
the
M-type
hexaferrites
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 with Pr-BiCo content (x) from 0.0 to 0.5.
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19. Fig.
4.
Representative
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Fig. 3. c/a ratios as a function of Pr-BiCo content (x) for the M-type hexaferrites
FE-SEM
micrographs
of
M-type
hexaferrite
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets for compositions of (a) x=0.0, (b) x=0.2,
Fig.
5.
Demagnetizing
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and (c) x=0.4.
curves
of
the
M-type
hexaferrite
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Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets for compositions of (a) x=0.0, (b) x=0.1,
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(c) x=0.2, (d) x=0.3, and (e) x=0.4, and (f) x=0.5. Fig. 6. The remanence (Br) as a function of Pr-BiCo content (x) for the M-type
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hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. Fig. 7. The magnetic induction coercivity (Hcb) and intrinsic coercivity (Hcj) as a
AC
function
of
Pr-BiCo
content
(x)
for
the
M-type
hexaferrite
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. Fig. 8. Hk/Hcj ratios as a function of Pr-BiCo content (x) for the M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. Fig. 9. The maximum energy product [(BH)max] as a function of Pr-BiCo content (x) for the M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets.
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Fig. 3
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Microstructural and magnetic properties of Pr-BiCo co-substituted M-type Sr-Ca hexaferrites Yujie Yang , Juxiang Shao , Fanhou Wang , Khalid Mehmood Ur Rehman , Jin Tang PII: DOI: Reference:
S0577-9073(17)31501-0 10.1016/j.cjph.2018.02.012 CJPH 458
To appear in:
Chinese Journal of Physics
Received date: Revised date: Accepted date:
21 November 2017 17 February 2018 27 February 2018
Please cite this article as: Yujie Yang , Juxiang Shao , Fanhou Wang , Khalid Mehmood Ur Rehman , Jin Tang , Microstructural and magnetic properties of PrBiCo co-substituted M-type Sr-Ca hexaferrites, Chinese Journal of Physics (2018), doi: 10.1016/j.cjph.2018.02.012
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ACCEPTED MANUSCRIPT Highlights
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 hexaferrites were prepared by standard ceramic method.
The hexaferrite grains have a hexagonal platelet shape with clear grain boundaries. Br first increases and then decreases with increasing Pr-BiCo content (x).
Hcj first decreases and then increases with increasing Pr-BiCo content (x).
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Microstructural and magnetic properties of Pr-BiCo co-substituted M-type Sr-Ca hexaferrites Yujie Yang ﹡ 1, Juxiang Shao1, Fanhou Wang1, Khalid Mehmood Ur Rehman2, Jin Tang2 Computational Physics Key Laboratory of Sichuan Province, School of Physics and
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1
Electronic Engineering, Yibin University, Yibin 644007, P. R. China 2
Engineering Technology Research Center of Magnetic Materials, School of Physics
& Materials Science, Anhui University, Hefei 230601, P. R. China
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Abstract
We have synthesized the Pr-BiCo substituted hexaferrites with compositions of Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 (0.0 ≤ x ≤ 0.5) by the standard ceramic method. Results of X-ray diffraction analysis exhibits that the synthesized hexaferrites with x
M
from 0.0 to 0.3 are in single magetoplumbite structure, and impurity phases are
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observed when x ≥ 0.4. The surface morphology of magnets shows that hexaferrite grains have a hexagonal platelet shape with clear grain boundaries. The remanence
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first increases with x from 0.0 to 0.1, and then decreases when x ≥ 0.1. The intrinsic coercivity decreases with x from 0.0 to 0.1, and then increases when x ≥ 0.1. With x
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from 0.0 to 0.4, the changing trend of magnetic induction coercivity is in agreement
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with that of Hcj, while at x ≥ 0.4, Hcb decreases. The maximum energy product initially increases with x from 0.0 to 0.2, and then decreases when x ≥ 0.2. Keywords: M-type hexaferrites; Pr-BiCo co-substitution; X-ray diffraction; Magnetic properties 1. Introduction ﹡
Corresponding author. Tel: +86 831 3531171, Fax: +86 831 3531161. E-mail address: [email protected] (Y.J. Yang). 2
ACCEPTED MANUSCRIPT M-type hexaferrites are the most utilized permanent materials due to their low price, moderate energy product, strong uniaxial anisotropy, and high Curie temperature [1]. The magnetic properties of M-type hexaferrites depend on the preparation conditions and the ion site occupation of the substituted ions. There are five different Fe3+ sublattices, such as one tetrahedral (4f1), one bipyramidal (2b) and
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three octahedral (2a, 12k and 4f2) [2]. In this respect, M-type hexaferrites have been the focus of many studies in order to improve their magnetic properties.
It is an effective method to modify the magnetic properties of M-type hexaferrites by the ion substitution. Many studied have been done on the M-type
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hexaferrites with partial substitutions of Sr2+ or Ba2+ ions and Fe3+ ions by several ions, such as La3+ [3], Pr3+ [4], Ce3+ [5], Nd3+ [6], Sm3+ [7], Gd3+ [8], Co2+ [9], Bi3+ [10], Al3+ [11], Cu2+ [12], and Zn2+ [13]. Wang et al. have prepared the Pr doped M-type
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strontium hexaferrite by hydrothermal synthesis and subsequent calculations and found that Pr substitution can increase the coercivity without leading to any distinct
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change in the magnetization [4]. Ezhil Vizhi et al. have synthesized the Co doped
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Ba-Sr hexaferrite Ba0.5Sr0.5Fe12-xCoxO19 (x = 0.0, 0.5, 0.7 and 0.9) by one-step citrate gel combustion method followed by annealing and found that the saturation
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magnetization (Ms) reaches to the maximum value at x = 0.5 [9]. Auwal et al. have reported that for the Bi3+ ions substituted M-type strontium hexaferrite SrBixFe12-xO19
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(0.0 ≤ x ≤ 1.0) synthesized using a co-precipitation assisted ceramic route, and a systemic change in the lattice parameters (a and c) was detected and the results of cation distribution exhibited that Fe3+ ions are distributed uniformly over the tetraand octahedral positions of spinel structure [10]. Many studied have been done on the M-type hexaferrites with combined substitution, such as La-Co [14], La-Zn [15], La-Ni [16], Nd-Co [17], Gd-Co [18], Ce-Co [19], Gd-Sn [20], Pr-Ni [21], Bi-Cr [22],
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ACCEPTED MANUSCRIPT Co-Zr [23], Co-W [24], and Mn-Zn [25]. Shen et al. have studied the La-Ni substituted M-type barium hexaferrites Ba1-xLaxFe12-xNixO19 (0.0 ≤ x ≤ 0.2) produced by the chemical co-precipitation method and found that the magnetoplumbite structure for all the samples have been formed, and Ms and Hc decrease with the increase of substitution content from 0.0 to 0.4 [16]. Iqbal et al. have synthesized the
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Pr-Ni doped M-type hexaferrites Sr0.5Ba0.5-xPrxFe12-yNiyO19 (0.00 ≤ x ≤ 0.10, 0.00 ≤ y ≤ 1.00) by the chemical co-precipitation method and found that the values of Ms and Mr increase with the substitution of Pr-Ni ions up to x = 0.06 and y = 0.60, and the coercivity shows a significant decrease with the substitution of Pr-Ni ions up to x =
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0.06 and y = 0.60 [21]. Shakoor et al. have synthesized the Bi-Cr substituted M-type strontium hexaferrites SrFe12-2xBixCrxO19 (0.0 ≤ x ≤ 0.8) by the sol-gel method and found that Ms and Mr first increases with the increase of Bi-Cr content from 0.0 to 0.2,
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and then decrease when Bi-Cr content ≥ 0.2; while Hc decreases with increasing Bi-Cr content from 0.0 to 0.2, and then increases when Bi-Cr content ≥ 0.2 [22]. Joshi et al. investigated
the
Co-W
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have
doped
M-type
Ba-Sr
hexaferrites
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Ba0.5Sr0.5CoxWxFe12-2xO19 (0.2 ≤ x ≤ 1.0) prepared by the ceramic method and found that SEM images and hysteresis loops of all samples exhibit multidomain particles,
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the coercivity decreases with Co-W content from 0.2 to 1.0 while Ms and Mr first decrease with Co-W content from 0.2 to 0.8 and then increase in x = 1.0 [24].
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In this paper, the element of Pr3+ is chosen to substitute the Sr2+ ions and the
elements of Bi3+ and Co2+ are chosen to substitute the Fe3+ ions. We have synthesized the Pr-BiCo substituted M-type Ca-Sr hexaferrites by the standard ceramic method. And the impacts of Pr-BiCo content on the microstructural and magnetic properties were carefully investigated. 2. Experimental procedure 4
ACCEPTED MANUSCRIPT The standard ceramic method were used to prepare the M-type Ca-Sr hexaferrites with nominal compositions of Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 (0.0 ≤ x ≤ 0.5). The raw materials used in this study were CaCO3 (99% purity), SrCO3 (99% purity), Pr6O11 (99% purity), Fe2O3 (99% purity), Bi2O3 (99% purity) and CoO (99% purity). They were used as such without further treatment. These raw materials were
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mixed together according to their molecular weight ratios, and were wet-grinded in a ball mill at a rotate speed of 80 rpm for 10 h. And the grinded powders were dried in a drying oven in the air, and then calcined in a muffle furnace at 1240 oC for 2.0 h. The calcined powders were shattered to particles, and were again wet-grinded with
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suitable additives (CaCO3, SrCO3, SiO2, Ca(C6H11O7)2) for 18 h in a ball-mill. After that, the finely grinded slurry was pressed into cylindrical pellets, and the pressed pellets were sintered in a muffle furnace at 1190 oC for 1.5 h in air.
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The phase compositions of the samples were confirmed by X-ray diffraction analysis which was carried out using a powder X-ray diffraction (XRD, Rigaku
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D/max-2550V/PC) Cu Kα (λ = 1.5406 Å) radiation. The 2θ angles were scanned over
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a range between 20o and 80o. The surface morphology of magnets was observed by a field emission scanning electron microscopy (FE-SEM, HITACHI S-4800). The
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magnetic properties of the samples were measured at room temperature by a permanent magnetic measuring system (NIM-2000HF, made by the National Institute
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of Metrology of China). 3. Results and discussion 3.1. Structural analysis Fig. 1 shows the X-ray diffraction patterns of the Pr-BiCo substituted M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnetic powders with Pr-BiCo
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ACCEPTED MANUSCRIPT content (x) from 0.0 to 0.5. The observed XRD peaks were indexed. It is seen that for the M-type hexaferrite magnetic powders with Pr-BiCo content (x) from 0.0 to 0.3, the XRD patterns belong to the M-type strontium hexaferrite (JCPDS card no. 80-1198). For the magnetic powders at Pr-BiCo content (x) ≥ 0.4, PrFeO3 is detected in the structure. For the magnetic powders at Pr-BiCo content (x) = 0.5, PrFeO3 and
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α-Fe2O3 are detected in the structure.
The lattice parameters (c and a) of M-type hexaferrites are calculated by the following equation [26]: 1 4 h 2 hk k 2 l 2 2, 2 d hkl 3 a2 c
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(1)
where dhkl is the d-spacing of the lines in XRD pattern and h, k and l are the Miller indices. The variations of the lattice parameters (c and a) as a function of Pr-BiCo content (x) for the M-type hexaferrites Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 are shown
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in Fig. 2. In the present study, one Pr3+ ion substitutes one Sr2+ ion, and both Bi3+ and
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Co2+ ions substitute two Fe3+ ions. It is seen that the lattice constant a is almost constant (5.8872-5.8902 Å) in the experimental errors with increasing the Pr-BiCo
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content (x), while the lattice constant c first increases with the increase of Pr-BiCo
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content (x) from 0.0 to 0.3, and then decreases when Pr-BiCo content (x) ≥ 0.3. The increase of lattice constant c with the increase of Pr-BiCo content (x) from 0.0 to 0.3
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can be attributed to the difference in the ionic radii (Δr) of the metal ions and the number of ionic substitutions of each species. Substitution of Sr2+ (r = 1.180 Å) by Pr3+ (r = 1.013 Å) makes a negative difference in the ionic radii of Δr = -0.167 Å. The ionic radius of Bi3+ was 1.030 Å and that of Co2+ was 0.745 Å, giving an average value of 0.8875 Å for equiatomic BiCo co-substitution. Thus, substitution of Fe3+ (r = 0.645 Å) by Bi3+-Co2+ (the average value of ionic radii is 0.8875 Å) makes a positive
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ACCEPTED MANUSCRIPT difference in the ionic radii of Δr = +0.2425 Å. In the Pr-BiCo substituted M-type hexaferrites, in order to keep the electroneutrality, some Fe3+ ions (r = 0.645 Å) will change into Fe2+ ions (r = 0.780 Å) at 2a or 4f2 site, this makes a positive difference in the ionic radii of Δr = +0.135 Å. As in the case of Pr-BiCo content (x = 0.2), the total content of both Co2+ and Fe2+ ions is equal to that of Pr3+ ions, and the lattice constant
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c is increased. When Pr-BiCo content (x) ≥ 0.4, PrFeO3 is detected in the structure, and at Pr-BiCo content (x) = 0.5, PrFeO3 and α-Fe2O3 are detected in the structure. The impurity phase peak intensity is increased with increasing Pr-BiCo content (x). Thus, the decrease of lattice constant c when Pr-BiCo content (x) ≥ 0.3 can attributed
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to the below reasons. Firstly, in order to keep the electroneutrality, less Fe3+ ions (r = 0.645 Å) will change into Fe2+ ions (r = 0.780 Å) at 2a or 4f2 site. Secondly, the impurity phases such as PrFeO3 and α-Fe2O3 induce lattice distortion for the
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hexagonal structure.
Fig. 3 shows the change of c/a ratios as a function of Pr-BiCo content (x) for the
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M-type hexaferrites Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19. From Fig. 3, it is observed that c/a ratios of M-type hexaferrites slightly increase with the increase of Pr-BiCo
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content (x) from 0.0 to 0.3, and then decrease when Pr-BiCo content (x) ≥ 0.3. The
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lattice constant ratio c/a can be used to quantify the structure type, and an M-type structure can be assumed if the ratio is lower than 3.98 [27]. The c/a ratios with
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different Pr-BiCo contents are in the range from 3.8976 to 3.9153, confirming the formation of M-type hexagonal structure. The
FE-SEM
micrographs
of
M-type
hexaferrite
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets for compositions of x=0.0, x=0.2, and x=0.4 are shown in Fig. 4. It is clearly seen that the hexaferrite grains have a hexagonal platelet shape with clear grain boundaries. The average grain sizes of the
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5 shows the
demagnetizing curves
of the M-type hexaferrite
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Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets with the increase of Pr-BiCo content (x) from 0.0 to 0.5. In Fig. 5, the blue lines are the intrinsic demagnetizing curves of the M-type hexaferrite magnets and the red lines are the normal demagnetizing curves of the M-type hexaferrite magnets [28]. The value of the intrinsic coercivity (Hcj) is
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larger than that of magnetic induction coercivity (Hcb). Hk is the value of the reverse magnetic field intensity corresponding to B=0.9 Br on the demagnetizing curves. The squareness ratio (Hk/Hcj), where Hk and Hcj are the knee field and intrinsic coercivity, respectively, is an important factor affecting the value of high anisotropy factor [29].
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The remanence (Br), intrinsic coercivity (Hcj), maximum energy product [(BH)max]
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and Hk/Hcj ratio are extracted from demagnetizing curves, and their values are listed in Table 1.
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The variation of the remanence (Br) as a function of Pr-BiCo content (x) for the
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M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets is shown in Fig. 6. It can be seen from Fig. 6 that the value of Br first increases with the increase of
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Pr-BiCo content (x) from 0.0 to 0.1, and then begins to decrease with the increase of Pr-BiCo content (x) from 0.1 to 0.5. In the M-type hexagonal ferrite, Fe3+ ions occupy five different crystallographic sites: three octahedral sites (12k, 4f2 and 2a), one geometric tetrahedron site (4f1), and one bipyramidal site (2b). The 2a, 2b and 12k sites have upward spin configurations, and the 4f1 and 4f2 sites have downward spin configurations. It is reported that Pr3+ ions substitute for Sr2+ ions [4], and Bi3+ ions substitute for Fe3+ ions in the 4f1, 4f2 [10], and Co2+ ions substitute for Fe3+ ions in the 8
ACCEPTED MANUSCRIPT 4f1, 4f2 and 2b sites [30]. The magnetic moment of Fe3+ ion is 5 μB. The magnetic moment of Co2+ ion is 3.7 μB. In the Pr-BiCo substituted M-type hexaferrites, in order to keep the electroneutrality, some Fe3+ ions will change into Fe2+ ions at 2a or 4f2 site. In this study, the increase of the remanence (Br) with Pr-BiCo content (x) from 0.0 to 0.1 can be ascribed to the following two reasons. Firstly, the non-magnetic Bi3+ ions
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occupy the site having spin of electrons in downward direction, which results in the number of Fe3+ ions having spin in upward direction. This leads to the increase of remanence (Br). Secondly, the occupancy of 4f1 and 4f2 sites by Co2+ ions is positive in inhibiting the offsetting of magnetic moment and leads to the increase of bulk
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magnetic moment. This results in the increase of the remanence (Br). However, when the Pr-BiCo content (x) ≥ 0.1, the decrease in the the remanence (Br) can be due to the below three reasons. Firstly, with the doping of Pr3+ ions instead of Sr2+ ions and Bi3+
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and Co2+ ions for Fe3+ ions, the Fe3+-O-Fe3+ superexchange interaction is weakened. This causes to magnetic collinearity to collapse, and leads to the decrease of
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remanence (Br). Secondly, the substituting of Fe3+ (5 μB) ions in the 2b sites by Bi3+ (0
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μB) and Co2+ (3.7 μB) ions and the change of Fe3+ (5 μB) ions to Fe2+ (4 μB) ions result in the decrease of bulk magnetic moment. This leads to the decrease of remanence
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(Br). Thirdly, in M-type hexaferrites, the impurity phases have almost no contribution to the increase of remanence (Br). When the Pr-BiCo content (x) ≥ 0.4, the appearance
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of impurity phases as shown in Fig. 1 can cause the remanence (Br) to decrease. Fig. 7 shows the variations of the magnetic induction coercivity (Hcb) and
intrinsic coercivity (Hcj) as a function of Pr-BiCo content (x) for the M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. It is seen from Fig. 7 that Hcj decreases with increasing Pr-BiCo content (x) from 0.0 to 0.1, and then increases with increasing Pr-BiCo content (x) from 0.1 to 0.5. According to the Stoner-Wohlfarth
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H c 0.64
2K , Ms
(2)
where K is the magnetocrystalline anisotropy constant and Ms is the saturation
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magnetization. Thus, the decrease of Hcj with Pr-BiCo content (x) from 0.0 to 0.1 can be due to the following two reasons. Firstly, according to the formula (2), the increase of remanence (Br) with Pr-BiCo content (x) from 0.0 to 0.1 results in the decrease of the coercivity. Secondly, the decrease of Hcj should be attributed to the decrease of
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uniaxial anisotropy constant because of the occupancy of the 4f2 and 2b sites by Co2+ ions. However, according to the equation (2), the increase of Hcj can be attributed to the decrease of remanence (Br) with increasing Pr-BiCo content (x) from 0.1 to 0.5 as
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shown in Fig. 6. It is also observed from Fig. 7 that for the magenets with Pr-BiCo content (x) from 0.0 to 0.4, the changing trend of Hcb is in agreement with that of Hcj,
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while for the magenets with Pr-BiCo content (x) ≥ 0.4, Hcb begins to decrease. The change of Hk/Hcj ratio as a function of Pr-BiCo content (x) for the M-type hexaferrite
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Ca0.2Sr0.8-xPrxFe12.0-x(Bi0.5Co0.5)xO19 magnets is exhibited in Fig. 8. The Hk/Hcj ratio
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can indicate the rectangularity of the demagnetizing curves for the magnets [31]. It is observed from Fig. 8 that for the magnets with Pr-BiCo content (x) from 0.0 to 0.3,
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the values of Hk/Hcj ratios are in the ranges between 0.938 and 0.972 and the changing trend of Hk/Hcj ratios is very slight, while for the magnets with Pr-BiCo content (x) ≥ 0.3, the value of Hk/Hcj ratio quickly decreases from 0.957 at x=0.3 to 0.554 at x=0.5. This shows that Pr-BiCo substitution has big influence on the rectangularity of the demagnetizing curves for the Pr-BiCo co-substituted M-type Ca-Sr hexaferrites as shown in Fig. 5. When Pr-BiCo content (x) ≥ 0.3, the quick decrease of Hk/Hcj ratio should be attributed to the presence of impurity phase in the structure as shown in Fig. 10
ACCEPTED MANUSCRIPT 1. The quick decrease of Hk/Hcj ratio at Pr-BiCo content (x) ≥ 0.3 may be the reason that Hcb begins to decrease when Pr-BiCo content (x) ≥ 0.4. Fig. 9 shows the change of the maximum energy product [(BH)max] as a function of Pr-BiCo content (x) for the M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. It is clearly seen that the value of (BH)max initially increases with increasing
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Pr-BiCo content (x) from 0.0 to 0.2, and then begins to decrease when Pr-BiCo content (x) ≥ 0.2. The maximum energy product of the M-type hexaferrites could be estimated by the product between the remanence (Br) and coercivity field.
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4. Conclusions
In the present study, the Pr-BiCo substituted M-type with nominal compositions of Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 (0.0 ≤ x ≤ 0.4) were synthesized by the standard ceramic method. We have carefully investigated the effects of Pr-BiCo
M
content on the structural and magnetic properties of the Pr-BiCo substituted M-type
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Ca-Sr hexaferrites. The major findings of this study were listed in the following: 1. X-ray diffraction analysis exhibits that when the Pr-BiCo content (x) increases from
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0.0 to 0.3, the synthesized M-type hexaferrite magnetic powders are in single magetoplumbite structure, and impurity phases are observed when Pr-BiCo content
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(x) ≥ 0.4. It is observed that the lattice constant a is almost constant with increasing
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the Pr-BiCo content (x), while the lattice constant c first increases with Pr-BiCo content (x) from 0.0 to 0.3, and then decreases when Pr-BiCo content (x) ≥ 0.3. The results of FE-SEM morphology exhibit that the hexaferrite grains have a hexagonal platelet shape with clear grain boundaries and the average grain size is increased with the increase of Pr-BiCo content (x). 2. Magnetization properties were measured at room temperature using a permanent magnetic measuring system. Br first increases with Pr-BiCo content (x) from 0.0 to 11
ACCEPTED MANUSCRIPT 0.1, and then decreases when Pr-BiCo content (x) ≥ 0.1. Hcj decreases with increasing Pr-BiCo content (x) from 0.0 to 0.1, and then increases when Pr-BiCo content (x) ≥ 0.1. With the increase of Pr-BiCo content (x) from 0.0 to 0.4, the changing trend of Hcb is in agreement with that of Hcj, while at Pr-BiCo content (x) ≥ 0.4, Hcb begins to decrease. (BH)max initially increases with increasing Pr-BiCo
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content (x) from 0.0 to 0.2, and then begins to decrease when Pr-BiCo content (x) ≥ 0.2. Acknowledgements
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This work was supported by the National Natural Science Foundation of China (Nos. 51472004, 51272003), Scientific Research Fund of SiChuan Provincial Education Department (No. 13ZA0918, No. 14ZA0267 and No. 16ZA0330), the Major Project of Yibin City of China (No. 2012SF034, No. 2016GY025 and No.
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2016 QD002), Scientific Research Key Project of Yibin University (No. 2015QD13)
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and the Open Research Fund of Computational Physics Key Laboratory of Sichuan
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Table 1. The remanence (Br), magnetic induction coercivity (Hcb), intrinsic coercivity (Hcj), maximum energy product [(BH)max] and Hk/Hcj ratio for M-type hexaferrites
Table 1
Hcj (kA/m) 148.5 122.9 139.1 185.9 203.4 239.9
(BH)max (kJ/m3) 28.56 29.32 30.21 28.33 19.41 10.20
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Hcb (kA/m) 145.4 118.0 137.5 180.2 194.4 158.8
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Br (mT) 404.1 417.5 405.9 384.4 321.6 236.3
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Pr-BiCo content (x) 0.0 0.1 0.2 0.3 0.4 0.5
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Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 with different Pr-BiCo content (x).
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Hk/Hcj 0.938 0.960 0.972 0.957 0.860 0.554
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Figure captions Fig.
1.
XRD
patterns
of
the
Pr-BiCo
substituted
Fig.
2.
Lattice
parameters
(c
and
a)
hexaferrites
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Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19.
M-type
of
the
M-type
hexaferrites
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 with Pr-BiCo content (x) from 0.0 to 0.5.
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19. Fig.
4.
Representative
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Fig. 3. c/a ratios as a function of Pr-BiCo content (x) for the M-type hexaferrites
FE-SEM
micrographs
of
M-type
hexaferrite
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets for compositions of (a) x=0.0, (b) x=0.2,
Fig.
5.
Demagnetizing
M
and (c) x=0.4.
curves
of
the
M-type
hexaferrite
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Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets for compositions of (a) x=0.0, (b) x=0.1,
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(c) x=0.2, (d) x=0.3, and (e) x=0.4, and (f) x=0.5. Fig. 6. The remanence (Br) as a function of Pr-BiCo content (x) for the M-type
CE
hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. Fig. 7. The magnetic induction coercivity (Hcb) and intrinsic coercivity (Hcj) as a
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function
of
Pr-BiCo
content
(x)
for
the
M-type
hexaferrite
Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. Fig. 8. Hk/Hcj ratios as a function of Pr-BiCo content (x) for the M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets. Fig. 9. The maximum energy product [(BH)max] as a function of Pr-BiCo content (x) for the M-type hexaferrite Sr0.8-xCa0.2PrxFe12.0-x(Bi0.5Co0.5)xO19 magnets.
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