Twofold and Fourfold Symmetric Anisotropic Magnetoresistance Effect in A Model with Crystal Field

Abstract

We theoretically study the twofold and fourfold symmetric anisotropic magnetoresistance (AMR) effects of ferromagnets. We here use the two-current model for a system consisting of a conduction state and localized d states. The localized d states are obtained from a Hamiltonian with a spin--orbit interaction, an exchange field, and a crystal field. From the model, we first derive general expressions for the coefficient of the twofold symmetric term ($C_2$) and that of the fourfold symmetric term ($C_4$) in the AMR ratio. In the case of a strong ferromagnet, the dominant term in $C_2$ is proportional to the difference in the partial densities of states (PDOSs) at the Fermi energy ($E_{\mathrm{F}}$) between the $d\epsilon$ and $d\gamma$ states, and that in $C_4$ is proportional to the difference in the PDOSs at $E_{\mathrm{F}}$ among the $d\epsilon$ states. Using the dominant terms, we next analyze the experimental results for Fe${}_4$N, in which $|C_2|$ and $|C_4|$ increase with decreasing temperature. The experimental results can be reproduced by assuming that the tetragonal distortion increases with decreasing temperature.

42 pages, 11 figures, to be published in J. Phys. Soc. Jpn. Vol. 84 (2015) No. 9, minor mistakes corrected

References in corpus (4)

• A theoretical analysis on highly spin-polarized transport of iron nitride Fe_4N
• Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe_4N, and Half-Metallic Ferromagnet: A Systematic Analysis
• Anisotropic Magnetoresistance Effect: General Expression of AMR Ratio and Intuitive Explanation for Sign of AMR Ratio
• Half-metallicity and anisotropy magnetoresistance properties of Heusler alloys Fe2Co1-xCrxSi

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