We study the device size dependence of spin-orbit torque induced magnetization switching in a Ta/CoFeB/MgO structure with perpendicular easy axis. The miniaturization of the device from micrometer-sized wire to 80-nm dot results in the increase of the threshold current density Jth by one order, whereas Jth increases only slightly with further reducing the device size down to 30 nm. No significant increase in Jth is seen, as the current pulse width decreases from 100 ms down to 3 ns. We reveal that the switching in devices at reduced size is reasonably well explained by the macrospin model, in which the effects of both the Slonczewski-like torque and field-like torque are included.

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A Ni-Cr nanocomposite with an average Cr concentration of 11 ͑wt %͒ was deposited onto nickel plate by simultaneous electrodeposition of Ni and Cr nanoparticles from a nickel sulfate bath. The nanocomposite consisted of a nanocrystalline Ni matrix and dispersed Cr nanoparticles with a mean size of 33 nm. For comparison, two Ni-Cr alloys, one with similar Cr content ͑10 wt %͒ and the other with much higher Cr content ͑20 wt %͒, were prepared using electro-arc melting. Hot corrosion testing under molten Na 2 SO 4 -K 2 SO 4 -NaCl in air at 700°C showed that rapid formation of a continuous chromia-rich scale is essential for hot corrosion protection. This was the case only for the nanocomposite. Internal sulfidation was observed for arc-melted alloys, but not for the nanocomposite. The results demonstrate that it was not primarily the Cr content but the unique structure of the nanocomposite that was responsible for its superior hot corrosion resistance. The protection mechanism lies in the fast formation of a continuous chromia scale on the nanocomposite, due to the easy nucleation of chromia on both chromium nanoparticles and abundant nickel grain boundaries, and then fast linking of the nuclei as a result of enhanced diffusion of Cr through those grain boundaries.

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