Shiho Nakamura

Giant magnetoresistance and soft magnetic properties of Co90Fe10/Cu spin‐valve structures

Spin‐valve structures with a magnetic material buffer layer, CoNbZr/NiFe/Co90Fe10/Cu/Co90Fe10/Fe50Mn50, were prepared on a oxidized Si substrate. From x‐ray diffraction analysis, it was shown that the CoNbZr/NiFe buffer layer enhances the fcc (111) orientation of the spin‐valve structure on oxidized Si. After annealing, the giant magnetoresistance (GMR) ratio of Δρ/ρ=8% and the soft magnetic properties of Hc=0.1 Oe and Hk=2.8 Oe were obtained. The sensitivity of GMR, Δ(Δρ/ρ)/ΔH, of 1.4%/Oe is achieved.

A New Ferromagnetic Amorphous Oxide of the La-Sr-Mn-B-O System

Amorphous 0.5La1-xSrxMnO3 0.5B2O3 (0.2≤x≤1.0) oxides were produced by melt quenching using a twin-roll technique. They were characterized by high crystallization temperatures above 920 K and transparency. Curie temperature is higher than 380 K over a wide range of Sr concentrations (0.3≤x≤1.0), thus differing from crystalline La1-xSrxMnO3 perovskite. The temperature dependence of magnetization in the amorphous state is similar to that for crystalline perovskite, suggesting ferromagnetism in the present amorphous oxides. The ferromagnetic behavior of the amorphous state may be explained by positive double-exchange interactions of Mn3+ and Mn4+ ions.

Current-Induced Magnetization Switching in Two Types of Nanopillar with Dual Fixed Layers

We study current-induced magnetization switching in nanofabricated magnetic multilayers with two different types of dual fixed layer structures. The first type is a single free layer with antiparallel aligned dual fixed layers. The second type is a synthetic antiferromagnetic (Syn.AF) free layer with parallel aligned dual fixed layers. In the former case, the switching current density (Jc) is reduced by a factor of more than two, as expected from our estimation. On the other hand, in the latter case, the dual structure does not reduce the Jc, which suggests the contributions of spin-dependent reflections and scatterings at various interfaces inside the free layer are significant. In some situations, they can reduce the total efficiency of the spin-transfer torque.

Lattice location study on H in Ta by the channeling method

By the channeling method using the nuclear reaction 1 H( 11 B, α)αα, the lattice location of H in TaH 0.07 (α-phase) was determined at room temperature, and the effect of strain on the hydrogen location was investigated by introducing internal strains by thermal cycling that gives rise to precipitation and redissolution of the β-phase. It is concluded that hydrogen atoms are located at tetrahedral sites in the α-phase of a Ta-H system, and the location does not change by such thermal cycling. Compared with the previous results on H in V and Nb, the present result indicates that the hydrogen location in Ta is less sensitive to the strain than in V as in the case of Nb.

Magnetization states of a spin-torque oscillator having perpendicular polarizer and planar free layer

The dynamics and magnetization structures of spin-torque oscillators (STOs) consisting of a planar free layer and a perpendicular polarizer and having diameters of 10–100 nm are investigated by micromagnetic and macrospin simulations. For models having a diameter of 50 nm, the current-dependent frequency exhibited three oscillation modes: uniform oscillation, continuous oscillation with edge-localized core of the z-component of the magnetization (Mz component), and non-continuous rotation. The uniform oscillation mode and edge-localized oscillation mode are distinguished from each other by observing the frequencies of the Mz components. Further, we found that the oscillation frequency of the edge-localized mode changed in a step-like fashion under an external magnetic field, which was not observed in the uniform oscillation mode. The frequency in the edge-localized mode became saturated as the current increased toward the non-continuous mode, with the trajectory of the core gradually moving toward the cen...

Dzyaloshinskii-Moriya interaction in Pt/Co/Pt films prepared by chemical vapor deposition with various substrate temperatures

We deposited perpendicularly magnetized Co(∼1nm)/Pt(6nm) bilayers by thermal chemical vapor deposition (CVD) on top of 3nm thick Pt layer using various deposition temperature. Observed Ms increased with the increase of deposition temperature Ts, and reached the value of pure-Co at Ts = 500°C. We measured a (left-handed) negative Dzyaloshinskii-Moriya interaction in CVD films indicating a dominant role of the bottom Pt/Co interface.

Relaxing-precessional magnetization switching

Abstract A new way of magnetization switching employing both the spin-transfer torque and the torque by a magnetic field is proposed. The solution of the Landau–Lifshitz–Gilbert equation shows that the dynamics of the magnetization in the initial stage of the switching is similar to that in the precessional switching, while that in the final stage is rather similar to the relaxing switching. We call the present method the relaxing-precessional switching. It offers a faster and lower-power-consuming way of switching than the relaxing switching and a more controllable way than the precessional switching.

High-purity cobalt thin films with perpendicular magnetic anisotropy prepared by chemical vapor deposition

A study of the chemical vapor deposition (CVD) of high-purity cobalt thin films is described. The Co layer prepared by a thermal CVD technique with a Pt/Ta underlayer and a Pt cap layer shows a saturation magnetization (Ms) of ~1.8 T and perpendicular magnetic anisotropy (PMA) with an anisotropy energy (Ku) of ~105 J/m3. The cobalt thickness dependence of Ku reveals that the interfacial anisotropy at the Pt/Co interface is most likely the origin of the obtained PMA.

A magnetic shift register with periodic potential energy modulation

For the first time, we demonstrated the intentional DW-position control and the shift operation of the 500-nm-long 7-bits in the magnetic shift register with the periodically potential energy modulated NW.

Hydrogen Trapping by Solute Atoms in Nb — Mo Alloys as Observed by the Channelling Method*

reported for various alloying elements/1,2/. For the mechanism of this enhancement a trapping model has been proposed/2,3/. On the other hand, it has been reported that no evidence for trapping was observed/4/, and it has been suggested that the enhancement is explained by using only the concept of macroscopic thermodynamics/5/. To elucidate the mechanism of this enhancement, in the present study the lattice location of hydrogen was investigated by the channelling method using a nuclear reaction ^H(^B, ) /6,7/ on the Nb alloys containing undersized Mo atoms (Nb-3at%Mo alloys). The experiments were performed with 11 2+ a 2.03 MeV beam, and channelling angular profiles of back11 scattered and emitted -particles were obtained for <100>, <110> and {100} channels. In the Nb-3at%Mo-2at%H alloy (specimen) the angular profiles of -particles ( -angular profiles) obtained at room temperature are very different from those for the tetrahedral (T) site occupancy obtained