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https://doi.org/10.1007/s11664-020-08423-0  2020 The Minerals, Metals & Materials Society

Effect of Thermal Oxidation on the Structural and Magnetic Properties of TbFe2 Alloys KRISHNA MANWANI,1 AROUT J. CHELVANE,2 and EMILA PANDA1,3 1.—Department of Materials Science and Engineering, Indian Institute of Technology, Gandhinagar, Palaj, Gujarat 382355, India. 2.—Advanced Magnetics Laboratory, Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058, India. 3.—e-mail: [email protected]

Because of its highest magnetostriction at room temperature, TbFe2 is one of the most promising materials for magnetostrictive applications. However, oxidation-induced deterioration in its magnetic properties limits its usage at higher temperature (T) and/or longer time (t). In this regard, a systematic study is performed here to understand the effect of oxide-film overgrowth (by varying T and t) on the microstructure and magnetic properties of TbFe2. The characteristic parameters of magnetic properties, such as coercivity (Hc) and remanent magnetization (Mr), are found to decrease with increasing T and/or t. Moreover, a strong correlation between the oxidation-induced microstructure and magnetic properties is observed. Understanding developed in this study will help in choosing optimum working conditions (i.e., T and/or t) for TbFe2 to avoid significant deterioration in the magnetic properties. Key words: TbFe2, magnetostriction, oxidation, microstructure, magnetic properties

INTRODUCTION Magnetostrictive TbFe2 (because of the largest magnetostriction value of 2500 9 10 6 at room temperature) has attracted significant attention as a promising material for several applications, like, microactuators, micromotors, sensors, etc.1–3 In addition, its high Curie temperature extends its application to higher temperatures.4,5 However, exposing the material to higher temperature leads to oxidation, which results in deterioration of its magnetic properties, thereby limiting its usage at elevated temperatures.6–8 In this regard, in our earlier work, we carried out a systematic study using both computations and experiments to understand the growth of oxides due to thermal oxidation of TbFe2.9 As a continuation of this earlier work, in the current study we have carried out systematic investigations to understand the effect of oxidation on the surface and magnetic properties of TbFe2.

(Received April 26, 2020; accepted August 14, 2020)

Although extremely relevant, only a very few studies are available in the literature.10–13 In this regard, studies were carried out by C. D. Wright et al.10–12 on  50-nm-thick amorphous Tb-Fe films to investigate the effect of oxidation on the magnetic properties of these films by varying the aging time (up to a t of 1400 h at 100C) and temperature [varying T from room temperature (RT) to 500C] in air. The magnetic properties of these films were found to degrade significantly due to the formation of oxide phases on their surface. Similarly, Van Dover et al. have shown deterioration in the magne