Magnetic behavior and characterization of La, Pr, and Bi substituted yttrium iron garnet

https://doi.org/10.1016/j.matchemphys.2020.124067Get rights and content

Highlights

  • The structural and magnetic properties of Bi, Pr, La, Dy:YIG were studied.

  • Bi can significantly assist doping other elements in YIG structure.

  • Super-exchange interaction was improved because of doping Bi in structure.

  • The saturation magnetization was improved as well.

Abstract

In this study, the structural and magnetic properties of rare-earth-doped garnets, RxY3-xIG (R = La, Pr, and Bi), prepared by the solid-state route were evaluated. Ce0.25Pr0.25Bi0.15Y2.35Fe5O12, Ce0.25Pr0.25Bi0.2Y2.3Fe5O12, Ce0.15Bi0.15La0.1Y2.6Fe5O12, Ce0.15Bi0.15La0.2Y2.5Fe5O12, Ce0.15Bi0.15Dy0.2Y2.5Fe5O12 and Ce0.25Pr0.5Bi0.15Y2.1Fe5O12 were prepared and compared with each other. The structural and microstructural studies were carried out using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The magnetic behavior was identified by a vibrating sample magnetometer (VSM). The XRD results revealed that the synthesized powders have a relatively high purity. The XPS data confirmed the minute amounts of impurities. A single garnet phase with a relatively high purity was formed in all the samples. The crystallite size was estimated using high resolution-TEM images with an average size of 20 nm. The samples with Bi3+cation show the maximum value of Ms in comparison with the samples containing La3+, Dy3+, and Pr3+ at about 35.26 emu/g due to the enhancement of the super-exchange interaction and the variation of the bond length and bond angle. Instead, in the samples with La3+, Ms decreases with the minimum amount for xLa = 0.2. As the La increased from 0.1up to 0.2, the Ms decreased from 31.03 to 28.60 emu/g. By increasing the Pr3+ content from 0.25 to 0.5, Ms increased from 29.31 to 33.16 emu/g as expected based on Neelʼs theory. In addition, by comparing the samples Ce0.15Bi0.15La0.2Y2.5Fe5O12 and Ce0.15Bi0.15Dy0.2Y2.5Fe5O12, it was found that in a fixed amount of dopants the Ms of the sample containing Dy is 31.14 emu/g, which is 2.08 more than that of the sample containing La. Generally, by comparing the samples with one another, it can be figured out that the sample with the chemical composition of Ce0.25Bi0.2Pr0.25Y2.3Fe5O12 shows the maximum value of saturation magnetization.

Introduction

After the exploration of the ferromagnetic materials, the yttrium iron garnet (YIG) attracted significant interest and due to its capability in the magnetic and magneto-optical field, new applications such as tunable filters and magneto-optical storages were introduced [[1], [2], [3], [4]]. YIG has a cubic crystallographic structure and in each unit cell, there are eight R3Fe5O12 formula units. R3+ cations occupy dodecahedral sites and almost all of the rare earth elements can occupy this site. Fe3+ ions occupy tetrahedral and octahedral sites and in the YIG lattice, three Fe3+ ions occupy tetrahedral sites and two Fe3+ ions occupy octahedral sites [5,6]. The magnetic moments of Fe3+ ions in these two positions align in an antiparallel manner. The magnetic behavior originates from this type of orientation [7]. Except for Fe3+, the other elements such as Cr, Al, Cu, etc, can be located at tetrahedral and octahedral sites [[8], [9], [10]]. It can be concluded from the number of published papers that YIG is the most attractive compound among rare-earth garnets (RIG) and that the interesting properties can be extracted from YIG by the substitution of different cations in its structure. Many researchers have studied the properties of pure and substituted YIG [[11], [12], [13], [14]]. Cheng et al. studied the effect of the La3+ ions on the magnetic properties of YIG. They reported that the maximum of the saturation magnetization is achieved at x = 0.2 [1]. Sharma and the coworkers investigated the magnetic and crystallographic properties of the La3+ doped YIG. They concluded that Ms is increased from 24.42 to 25.52 emu/g by enhancing the La3+ content up to x = 0.15 [15]. Zhao and the colleagues evaluated the magnetic properties of Bi-YIG prepared by the solid-state method. They figured out that the addition of Bi in the YIG structure can decrease the sintering temperature [16]. Lee and the co-workers considered the magnetic properties of BixY3-xFe5O12 (x = 0, 1, 2). They found out that the saturation magnetization increases as the Bi concentration increases up to x = 1. Based on Néel's theory, the Ms should not increase because Bi3+ is not a magnetic ion. On the other hand, with the addition of Bi3+ in YIG, since the ionic radius of Bi3+ (1.123 Å) is larger than Y3+ (1.016 Å), the bond length and bond angle of ions in the YIG structure changed. This variation in the bond length and bond angle enhanced the super-exchange interaction between Fe3+ ions at the octahedral and tetrahedral sites [17]. Xu and the colleagues investigated the effect of Ce3+ and Bi3+ on the structural properties of YIG. They reported that the addition of Ce3+ in the YIG structure leads to enhancing Ms in view of the fact that the magnetic moments of the Ce3+ ions in the dodecahedral location align parallel to the magnetic moments of the Fe3+ ions in the tetrahedral situation [18]. Yang and the coworkers evaluated the influence of adding Ce3+ ions upon the magnetic properties of YIG. They found out that the Ms of the pure YIG increases from 26 to 28 emu/g by adding Ce3+ ions up to x = 0.1 [19]. Niyayfar and coworkers studied the influence of the addition of Pr3+ on the YIG properties. They reported that by increasing the Pr3+ value from x = 0 to x = 0.2, the Ms content increases. They attributed this increase to the fact that the magnetic moment of Pr3+ ion is 3.2 μB and is oriented parallel with Fe3+ ions at the tetrahedral sites, leading to an increase in the saturation magnetization of YIG [20]. Cheng et al. reported that owing to the opposite alignment of the Dy magnetic moment with the magnetic moment of Fe at the tetrahedral sites, by increasing the Dy (10.6 μB) [21] the Ms is decreased [22]. Niaz Akhtar and colleagues presented that the substitution of Pr3+ in the YIG lattice enhances both the lattice parameter and Ms [23]. Dastjerdi et al. investigated as the Fetetra-O-Feocta angle is closer to 180° and as the length of Feocta-O is increased, the super-exchange interaction is evaluated [24].

In the current work, we investigated the magnetic properties and structural characterization of the La, Pr, and Bi substituted yttrium iron garnet produced by the solid-state route. The probability of the pure garnet phase formation and various cations oxidation states have been investigated. The purpose was to improve and compare the structural and magnetic properties of Bi, Pr, La, and Dy substituted YIG. It can be realized from this work that Bi can significantly assist doping other elements in YIG structure due to the charge compensation mechanism and also this work clarifies the improvement of superexchange interaction because of doping Bi in structure and consequently improving saturation magnetization despite this fact that Bi is a diamagnetic element.

Section snippets

Experimental procedure

The details of the materials used in this work were Fe2O3 (Merck 99.00%), Bi2O3 (Merck 99.99%), Y2O3 (Sigma-Aldrich 99.99%), Pr2O3 (Sigma-Aldrich 99.90%), CeO2 (US Research Nanomaterials Inc 99.97%), La2O3 (Merck 99.99%), and Dy2O3 (Sigma-Aldrich 99.99%).

In this study, the samples were prepared by the conventional ceramic technique. First, metal oxides with a suitable proportion were weighed and mixed. Then, the mixed powder was calcined at 1100 °C for 20 h in the air condition. The calcined

XRD evaluation

Fig. 1 depicts the XRD pattern of Ce0.25Pr0.25Bi0.15Y2.35Fe5O12, Ce0.25Pr0.25Bi0.2Y2.3Fe5O12, Ce0.15Bi0.15La0.1Y2.6Fe5O12, Ce0.15Bi0.15La0.2Y2.5Fe5O12, Ce0.15Bi0.15Dy0.2Y2.5Fe5O12 and Ce0.25Pr0.5Bi0.15Y2.1Fe5O12. The concentration of La, Pr, and Dy cations which are substituted in YIG structure has been chosen according to the past reports to investigate the effect of each one on the magnetic properties especially saturation magnetization. Cheng and coworkers studied the effect of La

Conclusion

In this work, the magnetic and structural properties and the effect of the bond length and bond angle on the magnetic properties of La, Pr, and Bi YIG have been compared with each other and the pure YIG. It is noteworthy that Feocta-O length and the Fetetra-O-Feocta angle can affect the magnetic behavior by influencing the super-exchange interaction of the Fe cations at the tetrahedral and octahedral sites and that Bi can improve the super-exchange interaction and the sample Ce0.25Bi0.2Pr0.25Y

CRediT authorship contribution statement

O. Dehghani Dastjerdi: Writing - review & editing, All the authors had a main role in preparation of this article, They wrote the whole article, presented the results including the figures and tables, discussed the results and improved the English language, All three authors had their own contribution in all of parts of preparing the article. H. Shokrollahi: Writing - review & editing, All the authors had a main role in preparation of this article, They wrote the whole article, presented the

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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