arXiv subjects

Hisazumi Akai

Publications and source records attributed to Hisazumi Akai.

22 records · Page 2Linked to original sources

arXiv2016

Relevance of $4f$-$3d$ exchange to finite-temperature magnetism of rare-earth permanent magnets: an ab-initio-based spin model approach for NdFe$_{12}$N

A classical spin model derived ab initio for rare-earth-based permanent magnet compounds is presented. Our target compound, NdFe$_{12}$N, is a material that goes beyond today's champion magnet compound Nd$_{2}$Fe$_{14}$B in its intrinsic magnetic properties with a simpler crystal structure. Calculated temperature dependence of the magnetization and the anisotropy field agree with the latest experimental results in the leading order. Having put the realistic observables under our numerical control, we propose that engineering $5d$-electron-mediated indirect exchange coupling between $4f$-electrons in Nd and $3d$-electrons from Fe would most critically help to enhance the material's utility over the operation-temperature range.

cond-mat.mtrl-sci↗

arXiv2014

Formulation of the augmented plane-wave and muffin-tin orbital method

A mixed basis all-electron full-potential method, which uses two kinds of augmented waves, the augmented plane waves and the muffin-tin orbitals simultaneously, in addition to the local orbitals, was proposed by Kotani and van Schilfgaarde in Phys. Rev. B81, 125117(2010). We named it the PMT method. In this paper, this mixed basis method is reformulated on the basis of a new formalism named as the 3-component formalism, which is a mathematically transparent version of the additive augmentation originally due to Soler and Williams in Phys. Rev. B47, 6784(1993). Atomic forces are easily derived systematically. We discuss some problems in the mixed basis method and ways to manage them. In addition, we compare the method with the PAW method on the same footing. This PMT method is the basis for our new development of the quasiparticle self-consistent $GW$ method in J.Phys.Soc.Jpn 83, 094711(2014).

cond-mat.mtrl-sci↗

arXiv2011

Enhancement of magnetism of Fe by Cr and V

Enhancement of magnetism of Fe that occurs by alloying with Cr or V is discussed on the basis of first-principles electronic structure calculation. The d states of Fe next to Cr(V) are pushed down to the lower energy side compared to those of pure Fe due to the hybridization with Cr(V) d states, which leads a Co-like electronic structure for the Fe atom. This enhances magnetic moments of other Fe atoms and also the exchange couplings among them. The same mechanism works as well for the magnetism of Fe/Cr heterostructures. The idea is extended to design of a new type of antiferromagnets with high Néel temperature. Such heterostructures could be used to increase a magnetic anisotropy of permanent magnets.

cond-mat.mtrl-sci↗

arXiv2003

A method to include the spin-fluctuation in the ab-initio electronic-structure calculation

We present a new method of ab-initio electronic-structure calculation including the spin-fluctuation (SF) self-consistently. We start from the Luttinger-Ward functional given as the sum of the LDA functional plus the temperature-dependent part of the SF energy functional. The size of interactions used in it are determined in a similar manner to the self-consistent renormalization theory by Moriya and Kawabata. Obtained paramagnetic susceptibilities on Pd, Ni, Fe, and fcc-Co above $T_c$ show rather good agreements with experiments.

cond-mat.str-el↗