Hirofumi Morise

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.

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.