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

doi:10.1016/j.jallcom.2018.06.255

Journal of Alloys and Compounds

Volume 765, 15 October 2018, Pages 616-623

https://doi.org/10.1016/j.jallcom.2018.06.255 Get rights and content

Highlights

•
First report of studies on Nd-NbZn co-substituted M-type Ca-Sr hexaferrites.
•
Studied the effects of Nd-NbZn content (x) on the formation of M-type hexaferrite phase.
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Magnetic measurements show a significant improvement in coercivity (H_c).
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Established an optimum Nd-NbZn co-substitution content to obtain single phase M-type hexaferrites.

Abstract

This is first report on Nd-NbZn co-substituted M-type Ca-Sr hexaferrites with nominal compositions Ca_0.4Sr_0.6-xNd_xFe_12.0-x(Nb_0.5Zn_0.5)_xO₁₉ (x = 0.00–0.32) fabricated by the conventional solid-state reaction method. X-ray diffractometer (XRD), Fourier transformer infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), physical property measurement system-vibrating sample magnetometer (PPMS-VSM) were employed to characterize M-type calcium-strontium hexaferrites. XRD patterns of the hexaferrites with Nd-NbZn content (x) of 0.00 ≤ x ≤ 0.16 showed the single M-type hexaferrite phase. However, for the hexaferrites with Nd-NbZn content (x) ≥ 0.24, the impurity phase (α-Fe₂O₃) was observed. FT-IR frequency bands in the range (592–613) cm⁻¹ and (430–470) cm⁻¹ corresponded to the formation of tetrahedral and octahedral clusters of metal oxides in the hexaferrites, respectively. FE-SEM micrographs showed that the grains were platelet-like shapes. The saturation magnetization (M_s) and magneton number (n_B) decreased with increasing Nd-NbZn content (x) from 0.00 to 0.32. The remanent magnetization (M_r) first increased with Nd-NbZn content (x) from 0.00 to 0.08, and then decreased when Nd-NbZn content (x) ≥ 0.08. The M_r/M_s ratio, coercivity (H_c) and magnetic anisotropy field (H_a) increased with increasing Nd-NbZn content (x) from 0.00 to 0.32. First anisotropy constant (K₁) first slightly increased with Nd-NbZn content (x) from 0.00 to 0.08, and then decreased when Nd-NbZn content (x) ≥ 0.08.

Introduction

Hexaferrites have been intensively investigated due to their wide applications, such as permanent magnetic materials, microwave devices, and magnetic recording media [1]. There are six possible different types of hexaferrites, namely M, W, Y, X, Z and U, depending upon their crystal structure. M-type hexaferrites (MFe₁₂O₁₉, M = Sr, Ba and Pb) are the mainstream of hexaferrites because of their low price, high saturation magnetization, high coercivity, and perfect chemical stability [[2], [3], [4]]. In the M-type hexaferrites, the Fe³⁺ ions are arranged in five crystal positions, such as three octahedral positions (12k, 4f₂ and 2a), one tetrahedral position (4f₁), and one trigonal bipyramidal positions (2b) [5].

The magnetic properties of M-type hexaferrites can be controlled and modified by the suitable cation substitution [6]. Several research works have been carried out to improve the their magnetic properties through the partial substitution of Sr²⁺ or Ba²⁺ ions by rare earth metals such as La³⁺ [7], Nd³⁺ [8], Sm³⁺ [9], Ce³⁺ [10], Ho³⁺ [11] and Pr³⁺ [12] ions, or Fe³⁺ ions by transition metals such as Zn²⁺ [13], Co²⁺ [14], Cu²⁺ [15], Cr³⁺ [16], Bi³⁺ [17] and Al³⁺ [18] ions. Mocuta et al. have synthesized Nd-substituted hexagonal ferrites Sr_1-xNd_xFe₁₂O₁₉ (0.00 ≤ x ≤ 0.20) using hydrothermal synthesis and found that the saturation magnetization and remanence remain almost constant while the coercivity (H_c) first increased with Nd content (x) from 0.00 to 0.08, and then decreased when Nd (x) ≥ 0.08 [8]. Vinnik et al. have prepared the Zn-substituted barium hexaferrites BaZn_xFe_12-xO₁₉ (0 ≤ x ≤ 0.065) single crystals and found that the saturation magnetization and coercivity turns out to depend very sensitive on the level of Zn-substitution [13]. Magnetic properties of M-type hexaferrites can be improved by simultaneous substitution of Sr²⁺ or Ba²⁺ ions by rare earth elements and Fe³⁺ ions by transition metal elements [[19], [20], [21], [22], [23]]. Herme et al. have synthesized the combined substitution of Nd-Co substituted strontium hexaferrites with the composition of Sr_1-xNd_xFe_12-xCo_xO₁₉ (x = 0.00–0.50) synthesized by the sol-gel auto-combustion method with further heat treatment and found that the coercivity (H_c) increased 11% with Nd-Co content (x) = 3, reaching to a maximum of 5480 Oe, while the saturation magnetization (M_s) was reduced 6% to 91 emu/g [22]. Moreover, many methods have been used to prepare the M-type hexaferrites, such as the solid-state reaction method [24], sol-gel technique [25], sol-gel auto combustion technique [26], Pechini method [27] hydrothermal method [28], self-propagating combustion method [29], and co-precipitation method [30]. In this study, the solid-state reaction method has been used to fabricate the M-type hexaferrites because of its many advantages, such as simplicity, high productive and well controllable grain size as compared with other methods.

However, the effects of Nd-NbZn co-substitution on magnetic properties of M-type calcium-strontium hexaferrites have not been reported. Thus, in this study, we have successfully synthesized Nd-NbZn co-substituted M-type hexaferrites Ca_0.4Sr_0.6-xNd_xFe_12.0-x(Nb_0.5Zn_0.5)_xO₁₉ (x = 0.00–0.32) by the conventional solid-state reaction method. The influence of Nd-NbZn co-substitution on the microstructural, spectral and magnetic properties of M-type Ca-Sr hexaferrites was systematically investigated for the first time. And M-type Ca-Sr hexaferrites with enhanced the remanent magnetization (M_r) and coercivity (H_c) were fabricated.

Section snippets

Materials

Calcium carbonate (CaCO₃) (99%), strontium carbonate (SrCO₃) (99.5%), neodymium oxide (Nd₂O₃) (99.9%), iron oxide (Fe₂O₃) (99.3%), niobium oxide (Nb₂O₅) (99.6%), zinc oxide (ZnO) (99%) were used as starting materials. All regents were used as received without further purification.

Synthesis of M-type hexaferrites

The Nd-NbZn co-substituted M-type Ca-Sr hexaferrites Ca_0.4Sr_0.6-xNd_xFe_12.0-x(Nb_0.5Zn_0.5)_xO₁₉ (x = 0.00, 0.08, 0.16, 0.24 and 0.32) were synthesized by the conventional solid-state reaction method. The starting

X-ray diffraction analysis

XRD patterns of the M-type Ca_0.4Sr_0.6-xNd_xFe_12.0-x(Nb_0.5Zn_0.5)_xO₁₉ (x = 0.00, 0.08, 0.16, 0.24 and 0.32) hexaferrites are shown in Fig. 1. XRD patterns of the Nd-NbZn co-substituted M-type hexaferrites were indexed using the standard patterns for the standard M-type hexagonal crystals (ICCD card no. 80–1198). As seen from Fig. 1, the M-type Ca_0.4Sr_0.6-xNd_xFe_12.0-x(Nb_0.5Zn_0.5)_xO₁₉ hexaferrites are single-phased M-type hexaferrites for the M-type Ca-Sr hexaferrites with Nd-NbZn content

Conclusions

Nd-NbZn co-substituted M-type Ca-Sr hexaferrites with nominal compositions Ca_0.4Sr_0.6-xNd_xFe_12.0-x(Nb_0.5Zn_0.5)_xO₁₉ (x = 0.00–0.32) were synthesized by the conventional solid-state reaction method. The impact of Nd-NbZn co-substitution on structural, spectral and magnetic properties of M-type calcium-strontium hexaferrites has been carefully investigated. XRD patterns of the hexaferrites with Nd-NbZn content (x) of 0.00 ≤ x ≤ 0.16 showed the single M-type hexaferrite phase. However, for the

Acknowledgements

This work was supported by the 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. 2016 QD002), Scientific Research Key Project of Yibin University (No. 2015QD13) and the Open Research Fund of Computational Physics Key Laboratory of Sichuan Province, Yibin University (No. JSWL2015KFZ04). This work was financially supported by the Natural Science

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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

Highlights

Abstract

Introduction

Section snippets

Materials

Synthesis of M-type hexaferrites

X-ray diffraction analysis

Conclusions

Acknowledgements

Prog. Mater. Sci.

Ceram. Int.

Chem. Eng. J.

Ceram. Int.

Mater. Sci. Eng. B

Ceram. Int.

Ceram. Int.

J. Alloys Compd.

J. Alloys Compd.

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

Mater. Chem. Phys.

Mater. Chem. Phys.

Res. Phys.

Mater. Res. Bull.

Ceram. Int.

J. Alloys Compd.

Ceram. Int.

Mater. Sci. Eng. A

Mater. Res. Bull.

J. Alloys Compd.

Ceram. Int.

J. Magn. Magn. Mater.

Influence of Nd-NbZn co-substitution on structural, spectral and magnetic properties of M-type calcium-strontium hexaferrites Ca_0.4Sr_0.6-xNd_xFe_12.0-x(Nb_0.5Zn_0.5)_xO₁₉