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The anisotropic magnetoresistance (AMR) effect was systematically investigated in epitaxially grown Co 2 Fe x Mn 1−x Si films against Fe composition x and the annealing temperature. A change of sign in the AMR ratio from negative to positive was clearly detected when x increased from 0.6 to 0.8. This sign reversal can reasonably be explained by the change in the dominant s-d scattering process from s↑ → d↑ to s↑ → d↓ caused by the creation of large d-states at the Fermi level, suggesting the disappearance of half-metallicity at x = 0.8. The variations in the remanent density of states in the half-metallic gap against annealing temperature are also discussed from the viewpoint of the AMR ratio on the basis of the s-d scattering model.

The magnetic damping constant in a series of Co2MnAlxSi1−x and Co2FexMn1−xSi Heusler alloy epitaxial films were systematically investigated by using ferromagnetic resonance technique. The determined magnetic damping constant is roughly proportional to the density of states at the Fermi energy of the first principle calculation. The result is consistent with the theoretical prediction when taking spin-orbit interaction into account. The small Gilbert damping constant for the fabricated films other than the Co2FexMn1−xSi film with x>0.6 can be originated in the half-metallic electronic structure of Heusler alloys.

We investigate the magnetocrystalline anisotropy (MCA) energy of tetragonal distorted FeCo alloys depending on the degree of order by first-principles electronic structure calculation combined with the coherent potential approximation. The obtained results indicate that the MCA energy of FeCo alloys strongly depends on the degree of order under optimal conditions, where the axial ratio of the bct structure is 1.25 and the composition is Fe 0.5 Co 0.5 . We find that the modification of the electronic structure resulting from electron scattering by chemical disorder has a considerable influence on the MCA under these conditions.

Magnetocrystalline anisotropy in transition metal alloys (FePt, CoPt, FePd, MnAl, MnGa, and FeCo) was studied using first-principles calculations to elucidate its specific mechanism. The tightbinding linear muffin-tin orbital method in the local spin-density approximation was employed to calculate the electronic structure of each compound, and the anisotropy energy was evaluated using the magnetic force theorem and the second-order perturbation theory in terms of spin-orbit interactions. We systematically describe the mechanism of uniaxial magnetocrystalline anisotropy in real materials and present the conditions under which the anisotropy energy can be increased. The large magnetocrystalline anisotropy energy in FePt and CoPt arises from the strong spin-orbit interaction of Pt. In contrast, even though the spin-orbit interaction in MnAl, MnGa, and FeCo is weak, the anisotropy energies of these compounds are comparable to that of FePd,. We found that MnAl, MnGa, and FeCo have an electronic structure that is efficient in inducing the magnetocrystalline anisotropy in terms of the selection rule of spin-orbit interaction.

We evaluate the magnetocrystalline anisotropy energy of L10 type FePt alloys with the lattice distortion and atomic disorder by using the first-principles calculation, which adopts the tight-binding linear muffin-tin orbital method in conjunction with the coherent potential approximation techniques. The calculated result indicates that the magnetocrystalline anisotropy energy is quite sensitive to the mentioned factors. In particular, it is drastically decreased with the degree of ordering compared with the expected value from the completely ordered structure. We will suggest that the improvement of the chemical ordering of the L10 crystal is one of the significant points to obtain a large magnetocrystalline anisotropy from FePt compounds.

The effect of strain on Néel temperature in corundum-type Cr2O3 and Fe2O3 was theoretically studied. We calculated the exchange coupling constants up to the fifth-nearest neighbors using the first-principles density functional method and evaluated the Néel temperature using Monte Carlo simulation of the classical Heisenberg model. We showed that the Néel temperature is enhanced (decreased) by tensile (compressive) strain along the c-axis. The Néel temperatures of Cr2O3 and Fe2O3 are enhanced more than 20 and 7% by 5% strain of the crystal lattice, respectively.

The effect of lattice strain on single-ion magnetic anisotropy and antiferromagnetic domain wall width in corundum-type Cr2O3 is studied using first-principles calculations and micromagnetics simulations. Without lattice strain, the domain wall width L DW is about 80 nm. When the lattice constant a is increased by 1–2%, L DW is reduced to less than 20 nm due to the increase in the single-ion anisotropy constant K 1 to on the order of 106 erg/cm3.