Giant heterogeneous magnetostriction in Fe-Ga alloys: Effect of trace element doping

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• 作者：Yangkun He^a ; Chengbao Jiang^a ; ^{jiangcb@buaa.edu.cn" class="auth_mail" title="E-mail the corresponding author} ; Wei Wu^a ; Bin Wang^a ; Huiping Duan^a ; Hui Wang^a ; Tianli Zhang^a ; Jingmin Wang^a ; Jinghua Liu^a ; Zaoli Zhang^c ; Plamen Stamenov^b ; J.M.D. Coey^a ; ^b ; Huibin Xu^a
• 关键词：Magnetostriction ; Fe&ndash ; Ga alloys ; Nanoheterogeneities ; Rare-earth crystal field interaction ; Synchrotron X-ray diffraction
• 刊名：Acta Materialia
• 出版年：2016
• 出版时间：1 May 2016
• 年：2016
• 卷：109
• 期：Complete
• 页码：177-186
• 全文大小：2653 K

文摘

Enhanced magnetostriction in iron-rich Fe–Ga alloys has been attributed to a heterogeneous nanostructure with tetragonal inclusions, although direct experimental evidence for their structure was lacking. Here we use transmission electron microscopy to show that melt-spun, (001) textured Fe₈₃Ga₁₇ ribbons contain 3 nm inclusions with c-axis Ga–Ga pairs aligned in a tetragonal L6₀-type structure; the induced tetragonality of the entire A2 matrix is observed directly by synchrotron X-ray diffraction. Trace doping with 0.2 atomic % nonmagnetic elements such as La or Pb increases the magnetocrystalline anisotropy and greatly enhances the magnetostriction. Rare-earth dopants from La to Lu produce a quarter-shell variation of the magnetic anisotropy; the crystal field parameter A₂⁰ is determined to be −15 Ka₀⁻². The best trace dopants are the light rare earths Ce and Pr that give a transverse magnetostriction of up to −800 ppm, as these elements soften the tetragonal modulus via their crystal field interaction. A new model is proposed to explain nanoheterogeneous magnetostriction, where the Ga–Ga pairs remain fixed, but the tetragonal axis of the matrix can be realigned in a magnetic field by a series of small deformations of the A2 matrix. These results signal a new approach to creating highly-magnetostrictive materials.