M. Nasui

Spin–orbit torques and magnetization switching in W/Co2FeAl/MgO structures

Magnetization switching by current induced spin–orbit torques (SOTs) in heavy metal/ferromagnetic metal/oxide structures is of great research interest due to its potential applications in the field of low power consumption spintronic devices. Here, we study the Slonczewski-like and the field-like SOT effective fields in β-W/Co2FeAl/MgO structures showing perpendicular magnetic anisotropy (PMA). We characterize the SOT effective fields using harmonic Hall voltage measurements and we point out the essential role of the planar Hall effect corrections. We estimate that for bulk β-W an effective spin Hall angle as large as 0.3 ± 0.03 and a spin diffusion length of 2.2 ± 0.3 nm. Moreover, we demonstrate SOT-induced magnetization switching for charge current densities of the order of 106 A cm−2.

Microwave Measurements of Pinning Properties in Chemically Deposited YBCO/BZO Films

We present a comparative study of vortex pinning in chemically deposited YBa2Cu3O7-x/BaZrO3 nanocomposite films, with the aim of correlating the preparation method to the superconducting properties. Two sets of samples have been prepared by different low fluorine routes (one set followed the in situ approach), with different starting YBCO coating solution and with a different amount of BaZrO3. The short-range vortex pinning properties have been assessed using a contactless microwave (48 GHz) technique, which yielded the vortex pinning constant (Labusch parameter) kp and the vortex viscosity θ as a function of the applied field up to 0.8 T, and for temperatures between 60 K and Tc. The results were compared to more usual (long-range vortex motion) Jc measurements. Despite the supposed similarity in pinning as determined from Jc, we found significant differences between the pinning properties of the two sets of samples. It appears that the in situ approach results in stronger pinning at microwaves in the whole temperature range explored, and that this behavior is due to the smaller dimensions of BaZrO3 nanoparticles. This information can be very useful in the search of optimized chemical route to strong pinning superconducting nanocomposite materials.