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Magnetostriction with Wannier functions: rare-earth orthoaluminates

2016 Joint MMM-Intermag Conference

2016.1.11-15
(2015.11.17 更新)

Pavel Novák (ASCR)

概要/Abstract

Rare-earth ions in a compound can produce both large magnetic anisotropy and largemagnetostriction. The magnetic anisotropy is due to the interaction between their anisotropic 4felectron clouds with the crystal electric fields of surrounding charges. This interactionaccompanied with spin-orbit coupling produces an energetically favored alignment of the REmagnetic moments along a specific crystalline direction. Simultaneously, the neighboring ionssurrounding the rare-earth ion experience forces when the 4f cloud is rotated, resulting instructural change, that is, linear magnetostriction. Thus to reveal the relation between themagnetic anisotropy and magnetostriction is not only of scientific interest but also of value for thetechnical development of stronger permanent magnets. During the last three years a novel method to calculate the crystal field of the rare-earth ions insolids was developed [1-5]. The method starts with the band structure calculation followed by atransformation of the Bloch to Wannier functions. From the Hamiltonian expressed in the Wannierbasis the crystal field parameters are determined. Finally an atomic-like Hamiltonian involving thecrystal field, 4f electron correlation, spin-orbit coupling and Zeeman interaction is used todetermine the rare-earth multiplet splitting and magnetism. Until now the method has been applied to more than sixty rare earth (R) containing compounds: Rimpurities in YAlO3 [1], LaF3 [2], yttrium aluminium and yttrium lutetium garnets [3], orthorhombicperovskites RGaO3, RCoO3 [4] and RMnO3 [5]. The calculated results agree remarkably well withthe experiment: the crystal-field-split multiplet levels within a few meV and magnetic propertiesare correctly described as well. In the present contribution the dependence of the crystal field on the distortion of the crystal isdetermined for RAlO3 (R=Tb, Dy and Gd) orthoperovskites. From energy levels obtained by thediagonalization of the atomic-like Hamiltonian the dependence of the R free energy on the strain iscalculated, which allows the determination of the magnetostriction. The results are compared withthe experiment of Kadomtseva et al. [6].References1 P. Novák, K. Knížek, J. Kuneš, Phys. Rev. B 87 (2013) 205139.2 P. Novák, J. Kuneš, K. Knížek, Opt. Mater. 37 (2014) 414.3 E. Mihokova, P. Novák, and V.V. Laguta, submited to J. Rare Earths.4 P. Novák, K. Knížek, M. Maryško, Z. Jirák and J. Kuneš, J. Phys.-Condens. Mat. 25 (2013)4460001.5 P. Novák, V. Nekvasil, K. Knížek, J. Magn. Magn. Mater. 358-359 (2014) 228.6 A.M. Kadomtseva, I.B. Krynetsky, and M.D. Kuzmin, J. Magn. Magn. Mater. 81 (1989) 196.



元素戦略拠点

触媒・電池元素戦略拠点
触媒・電池元素戦略研究拠点 (京都大学)
東工大元素戦略拠点
東工大元素戦略拠点 (東京工業大学)
構造材料元素戦略研究拠点
構造材料元素戦略研究拠点 (京都大学)
高効率モーター用磁性材料技術研究組合
高効率モーター用 磁性材料技術研究組合