Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control.

The demonstration of the charge-to-spin conversion, especially with enhanced spin Hall conductivity, is crucial for the development of energy-efficient spintronic devices such as spin-orbit torque (SOT) based magnetoresistive random access memories. In this work, fully epitaxial Ru/Cu heterostructures were fabricated with interface engineering and nanolayer insertions consisting of Cu (1 nm)/Ru (1 nm) structures with different numbers of periods. The atomically controlled interface was confirmed by the high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the epitaxial relationship persists even in the hybrid nanolayer insertion structures. The spin current generation was detected by the measurement of unidirectional spin Hall magnetoresistance, and the effective damping-like spin Hall efficiency (ξDL) was further quantitatively evaluated by the spin-torque ferromagnetic resonance with thickness dependence of the ferromagnetic layer. It is found that the sharp interface Ru/Cu film has a sizeableξDLof -2.2% and the insertion of Cu/Ru nanolayers at the interface can increase theξDLvalue to -3.7%. The former could be attributed to the interface spin-orbit filtering effect and the latter may be further understood by the intrinsic contribution from the local electronic structure tuning due to the lattice distortion near the interface. A large effective spin Hall conductivity is achieved to be (3∼5) × 105ℏ2eΩ-1m-1in the epitaxial Ru/Cu hybrid nanolayers, which is in the same range as that of platinum. This work indicates that the interfacial control with hybrid nanolayer structures can extend the SOT-based materials to highly conductive metals, even with weak spin-orbit interactions, toward high stability, low cost, and low energy consumption for spintronic applications.

Observation of Gyromagnetic Spin Wave Resonance in NiFe Films.

This Letter demonstrates spin wave resonance (SWR) owing to the gyromagnetic effect by propagating a Rayleigh-type surface acoustic wave (R-SAW) through ferromagnetic thin films. The SWR amplitude in a NiFe film shows a higher-order frequency variation than in a magnetoelastic Ni film. This frequency dependence is well understood in terms of the presence of a gyromagnetic field attributable to the local lattice rotation in the R-SAW. From the frequency dependence of the SWR amplitude, the gyromagnetic SWR could be separated from another SWR caused by a magnetoelastic effect of the ferromagnet.

Nonreciprocal Spin Current Generation in Surface-Oxidized Copper Films.

We experimentally demonstrate the nonreciprocal generation of spin current (J_{s}) in a surface-oxidized copper film. The efficiency of conversion is at least 320 times larger than the inverse conversion. This nonreciprocity is due to a novel type of J_{s} generation, which relies on the transfer of angular momentum from the velocity field of free electrons. A gradient in the electrical mobility in the film produces vorticity in the in-plane drift velocity of the free electrons. The inverse process can hardly occur when J_{s} is collinear with the gradient in the electrical mobility.

Modulation of magnetization dynamics in an epitaxial Heusler ferromagnet due to pure spin current in a laterally configured structure.

Using a laterally configured structure, we demonstrate modulation of the magnetization dynamics of an epitaxial Heusler ferromagnet, Fe3Si, by nonlocally injecting pure spin currents. From the ferromagnetic resonance signals, the effective Gilbert damping constant ([Formula: see text]) of the epitaxial Fe3Si nanomagnet is estimated to be ∼0.003 at room temperature. By using the lateral and nonlocal spin injection, the [Formula: see text] value of the epitaxial Fe3Si nanomagnet can be modulated from 0.0034 to 0.0024. This study will open a way for control of the magnetization dynamics of high-performance ferromagnetic Heusler alloys due to pure spin currents even in laterally configured structures.

Spin wave-assisted reduction in switching field of highly coercive iron-platinum magnets.

Recent rapid progress in spintronic and magnetic storage nanodevices has required nanomagnets to balance competing goals for high coercive field and low switching field. However, a decisive route for highly efficient magnetization switching has not been established yet. Here we propose a novel switching method using a spin wave of magnetic structures twisted in a nanometre scale. We have experimentally demonstrated extremely low field-magnetization switching in a highly coercive FePt by using a spin wave excited in a soft magnetic permalloy (Ni81Fe19), where permalloy is exchange-coupled to FePt through the interface. We can tune the switching field by varying the magnitude and frequency of the radio frequency magnetic field, and a significant decrease in switching field by one order of magnitude is achieved under the optimum conditions. The spin wave-assisted magnetization switching is a promising technique for ultralow-energy magnetization manipulation.