Sho Yasuda

Bio: Sho Yasuda is an academic researcher from University of Tsukuba. The author has contributed to research in topics: Density functional theory & Magnetization. The author has an hindex of 1, co-authored 2 publications receiving 3 citations.

First-Principles Study of Magnetic Properties of Co/Pt(111) Film in Electric Field

Abstract: Technology of electric field (EF) control of magnetic properties is attractive for spintronic devices. In particular, it has been shown that the EF can change the magnetization and the magnetic anisotropy. According to an experimental study, an EF less than 0.1V/nm causes a large change of 40% in the magnetic anisotropy energy (MAE) of the Fe/Au(001) film. Also, another experimental study using the Co/Pt(111) film in the EF has shown that the Curie temperature of the film is changed up to 6K by applying an EF of about +0.2V/nm while down to 6K by applying an EF of about 0:2V/nm. A first-principles study of the MAE in the EF for the Fe/ Pt(001) film was carried out; it has been found that the change in the MAE is in proportion to the EF with the slope rate of 0.03meV/Fe per V/nm for Fe/Pt(001). Another firstprinciples study of the MAE in the EF for the Fe monolayer was carried out; it has been found that the MAE is affected considerably by applying the EF. On the other hand, to our knowledge, there are no first-principles studies of the Co/ Pt(111) film in the EF although the Co films are as important as the Fe films. In this study, we investigate the magnetic properties of the Co/Pt(111) film in the EF carrying out the first-principles calculations. We take account of the EF by introducing electrode far above Co/Pt(111) and changing the total number of electrons in the film. We calculate the spin moments and the numbers of electrons of the constituent atoms as well as the MAE of the film self consistently. We employ the fully relativistic full-potential linearcombination-of-atomic-orbitals method based on the density-functional theory within the local spin density approximation. The exchange-correlation energy functional used in this study is the Perdew–Wang parameterization of the Ceperley–Alder results. As shown in Fig. 1, the Pt(111) surface is modeled by a three-layer slab. We denote the Pt atoms in the top, middle, and bottom Pt layers by Pt(I), Pt(II), and Pt(III), respectively. We assume hcp stacking of the Co adlayer on the Pt(111) surface because the Co adatom prefers to occupy an hcphollow site on the Pt(111) surface. We use the lattice constant of the triangular lattice, 2.78 A, which is calculated from the lattice constant of fcc Pt, 3.92 A. All the interlayer distances between adjacent atomic layers of Co/Pt(111) are optimized calculating the forces acting on the Co and Pt atoms in the absence of the EF. The optimized interlayer distances are shown in Fig. 1. The EF is applied as follows. We change the total number of electrons in the film; we denote this change per Co atom by N. We introduce the following external potential originated in the electrode shown in Fig. 1:

Dependence of Structural and Electronic Properties of Uranium Monochalcogenides on Exchange–Correlation Energy Functionals

Abstract: We study the dependence of the structural properties of uranium monochalcogenides, U X where X = S, Se, and Te, as well as their electronic ones on the exchange–correlation energy functionals within the spin density functional theory, carrying out all electron calculations by the fully relativistic full-potential linear-combination-of-atomic-orbitals method. We employ two functionals of the local spin density approximation (LSDA) and two functionals of the generalized gradient approximations (GGA); the former two are the Perdew–Zunger and Perdew–Wang functionals and the latter two are the Perdew–Burke–Ernzerhof (PBE) and PBEsol functionals. We also examine the effects of the relativistic correction to the LSDA exchange part of each functional. We find that, for lattice constants, bulk moduli, and cohesive energies, the results of the calculations using the PBE functional are in the best agreement with the experimental results. On the contrary, we find that calculated total magnetic moments and one-electro...

Sign Reversal of Electric Field Effect on Coercivity in MgO/Co/Pt System

Abstract: The authors have investigated the effect of film deposition conditions on the electric field modulation of the coercivity in a perpendicularly magnetized MgO/Co/Pt system. In samples with the MgO capping layer deposited using high rf-sputtering power, the direction of coercivity change caused by applying an electric field was opposite to that in the previous results on the same system. This result indicates that the film deposition condition can strongly affect the electrical control of magnetic properties.

First-Principles Study of Electric Field Effects on Magnetic Anisotropy in MgO/TM/Au (TM = Fe, Co) Systems

Abstract: We study the electric field (EF) effects on the magnetic anisotropy in the MgO/TM/Au (TM = Fe, Co) systems with (001) and (111) orientations using relativistic first-principles calculations based on the density functional theory. We find that the perpendicular magnetic anisotropy of the MgO/TM/Au(001) system is enhanced by the EF that decreases the number of electrons in the system. The magnetic anisotropy energy (MAE) and its EF dependence of the MgO/Fe/Au(001) system is found to be in a semi-quantitative agreement with the experimental results with successful reproduction of the sign of the measured EF dependence. Furthermore, the EF dependence of the MAE of the MgO/Co/Au(001) system is found to be very large due to the structural relaxation of the Co–O interatomic distance and the decrease in the number of electrons in the Co atom caused by the EF. This result is attributed to the general trend that the perpendicular magnetic anisotropy of the Co layer is affected significantly when in contact with an ...

First-Principles Study of Electric Field Effects on Magnetic Anisotropy in Ultrathin Ferromagnetic TM (TM = Fe, Co) Films on Pt(111) Underlayer

Abstract: We study the electric field (EF) effects on the magnetic anisotropy in the ultrathin ferromagnetic TM (TM = Fe, Co) films on the Pt(111) underlayer using relativistic first-principles calculations based on the density functional theory with a special attention on the effects of Pt segregation. The magnetic anisotropy energy, MAE, and the spin magnetic moment, Mspin, of the Pt/TM/Pt(111) and BeO/Pt/TM/Pt(111) systems as well as those of the TM/Pt(111) and BeO/TM/Pt(111) systems are calculated in the absence of or under the EF. It is found that the MAE and its EF dependence of the BeO/Pt/TM/Pt(111) systems, especially those of the BeO/Pt/Co/Pt(111) system, are considerably large. The sign of the EF dependence is such that the MAE and Mspin are increased (decreased) when the EF increases (decreases) the number of electrons in the system. We attribute this unique behavior to the formation of the hybridized majority-spin states originated in the O 2pz, Pt \(5d_{3z^{2} - r^{2}}\), and TM 3d orbitals of the inte...

X-ray Magnetic Circular Dichroism Spectra for Uranium Monochalcogenides, UQ (Q = S, Se, and Te) from First Principles

Abstract: In this study, by applying relativistic full potential density functional theory with the generalized gradient approximation (GGA), GGA + U, and GGA + OP (orbital polarization) methods, we have investigated the magnetic properties of uranium monochalcogenides, UQ (Q = S, Se, and Te). The emphasis here is to calculate X-ray magnetic circular dichroism (XMCD) spectra of U in UQ systems at the U M45, N45, and L23 edges and compare the spectra as well as deduced parameters such as spin, orbital, and total magnetic moments with the available experimental and computational results. The effect of the Hubbard (U) parameter on the 5f electrons of uranium is also scrutinized to probe the electron correlation effects in UQ for their electronic and magnetic properties. The spin and orbital sum rule analyses have been carried out on the computed U M45 and N45 XMCD spectra. The corresponding spin, orbital, and total magnetic moments and the ratio of orbital and spin magnetic moments determined for UQ systems are found to be in good agreement with experiments when we use the GGA + OP method.