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We study a growth technique of non-collinear antiferromagnetic Mn3Sn thin films deposited by sputtering with various substrates and underlayers. The relation between their crystal structure and magnetic/transport properties is also investigated. We achieve the formation of epitaxial films with both C-plane and M-plane orientations, whose Kagome lattices are parallel and perpendicular to the plane, respectively. Transverse resistivity originating from the anomalous Hall effect shows different trends reflecting the Kagome lattice orientation of each stack. The established technique and findings offer a platform to study functional devices utilizing the unconventional physical properties of non-collinear antiferromagnets with controlled Kagome lattice orientation.

We investigate the electric-field effect on the magnetic anisotropy in perpendicularly magnetized Pt/Co/Pd/MgO structures deposited on GaAs and Si substrates as a function of temperature. An electric field is applied to the Pd surface through a 2-nm-thick insulating MgO layer by forming an electric double layer using an ionic liquid. We find that the electric-field dependence of the anisotropy is similar but clearly different between the two samples at low temperatures. The difference is expected to be related to the difference in the internal strain of the two structures.

We report on molecular beam epitaxy and properties of a magnetic topological insulator, Cr doped Sb2Te3. The composition analysis reveals that Cr replaces Sb site, and x-ray diffraction confirms that single phase textured crystal structure can be obtained for (CrxSb1-x)2Te3 with x up to 0.44. Further increase in x results in phase separation or precipitates in the material. The Curie temperature TC increases with x up to 0.44, and reaches to 250 K, which is the highest TC observed till now in magnetically doped topological insulators., Comment: 9 pages, 3 figures

We investigate the magnetic properties of Fe100− x V x /MgO-based structures with a V composition x up to 20 at. %. The introduction of V results in the reduction of spontaneous magnetization, the damping constant, and both interfacial and bulk perpendicular magnetic anisotropies. However, the insertion of thin Fe layers at the FeV/MgO interfaces results in an effective perpendicular magnetic anisotropy as large as that of Fe/MgO. The result shows potential for lowering the threshold current for magnetization switching in FeV/MgO-based magnetic tunnel junctions, while maintaining a thermal stability factor similar to that in Fe/MgO-based junctions.

We demonstrate associative memory operations reminiscent of the brain using nonvolatile spintronics devices. Antiferromagnet–ferromagnet bilayer-based Hall devices, which show analogue-like spin–orbit torque switching under zero magnetic fields and behave as artificial synapses, are used. An artificial neural network is used to associate memorized patterns from their noisy versions. We develop a network consisting of a field-programmable gate array and 36 spin–orbit torque devices. An effect of learning on associative memory operations is successfully confirmed for several 3 × 3-block patterns. A discussion on the present approach for realizing spintronics-based artificial intelligence is given.

We investigate the damping constant of a free layer with a perpendicular magnetic easy axis in nanoscale CoFeB/MgO magnetic tunnel junctions (MTJs) with a reference layer with an in-plane easy direction. The built-in noncollinear magnetization configuration in the MTJs allows us to measure homodyne-detected ferromagnetic resonance without tilting the magnetization direction of the free layer from the device normal. The damping constants determined from the spectral linewidths after the subtraction of the inhomogeneous broadening are nearly independent of the device diameter ranging from 70 to 100 nm, and take values similar to those reported for blanket CoFeB films.

We present evidence of a localized magnetic domain-wall (DW) oscillator in Co/Ni nanowires. It is found that a DW is localized by the simultaneous application of a high magnetic field larger than the depinning field and a dc current smaller than the threshold current. A one-dimensional model and micromagnetic simulation reveal that the localized DW is in a precessional mode. Our results suggest that a localized magnetic DW oscillator can be realized by appropriately adjusting the magnetic field and dc current.

Two important mechanisms for current-induced domain wall (DW) dynamics, namely, precessional DW motion driven by the adiabatic spin transfer torque and steady DW motion induced by the spin Hall torque, have been proposed and experimentally confirmed. However, the effect of the spin Hall torque on precessional DW motion has not been reported yet. Here, we show that the spin Hall torque affects the precessional DW motion when the in-plane field is applied. It is found that the in-plane field induces a half rotation time difference during DW precession, which gives rise to the nonvanishing spin Hall torque on the precessional DW motion.

We measure dc voltages in a permalloy (Py) single layer and a Py/Pt bilayer under ferromagnetic resonance. The observed voltages can be decomposed into symmetric and antisymmetric components. First, we confirm for Py that the symmetric component results from the planar Hall effect (PHE), whereas the antisymmetric one results from the anomalous Hall effect. Then, we consider the dc voltage induced by the inverse spin Hall effect (ISHE) in Py/Pt superimposing the galvanomagnetic effects, and conclude that the voltage induced by ISHE also contributes to the symmetric component with about 2.5 times smaller magnitude than that by PHE. Our results indicate that one should be careful about the galvanomagnetic effects in the quantitative analyses of dc voltage induced by spin pumping.

Using time- and spatially-resolved Kerr microscopy, we directly measure the spatiotemporal evolution of photoexcited local spins of a two-dimensional electron gas in a modulation-doped GaAs/AlGaAs quantum well with a top gate electrode. The spatial pattern of spins after diffusion is controlled by a gate voltage that changes the strength of the spin–orbit interaction (SOI) field. By measuring the time dependence of spin distribution with an external magnetic field, we successfully observe a persistent spin helix state by tuning the gate voltage, and we obtain both Rashba and Dresselhauss SOI parameters separately.

We show that the angle-dependent Hall measurement is an effective method to determine the current-induced effective fields by investigating MgO/Fe/Ta and MgO/Fe/Pt/Ta multilayer structures. The experimentally obtained Hall resistance under a relatively large dc electrical current is well described by considering two components of current-induced effective fields, which may be related to the spin Hall effect and the Rashba effect. The directions of the effective fields are consistent with and their magnitudes are comparable to those reported previously for similar multilayer structures.

We investigate the magnetic properties of CoNi and CoPt films prepared by an alternate monoatomic layer deposition and discuss the possible existence of a metastable superlattice structure. We find that, as has been reported for the CoPt and CoPd films, the CoNi film also exhibits a perpendicular magnetic anisotropy when the monoatomic Co and Ni layers are stacked alternately, suggesting the possible formation of superlattice structure. Since the CoNi film contains neither noble nor rare-earth metals, it should be an attractive material system for applications.

The junction diameter D dependence of effective magnetic fields in a recording layer of CoFeB–MgO magnetic tunnel junctions with perpendicular magnetic easy axis is evaluated by ferromagnetic resonance measurements using the homodyne detection technique. The effective perpendicular magnetic field increases with decreasing D, which reflects mainly the reduction of the demagnetizing factor normal to the film plane. The stray field from a reference layer also increases with reducing D, which is in agreement with the D dependence of the shift field of the center of minor resistance versus perpendicular magnetic field curves with respect to zero magnetic field.

Electrical coherent manipulation of a quadrupolar-split nuclear spin ensemble in a GaAs quantum well (QW) with an rf electric field is demonstrated by the optical time-resolved Kerr rotation technique. Rabi oscillations and phase control between two spin-3/2 states are demonstrated by nuclear electric resonance in a gated GaAs QW device. This enables us to achieve coherent control of geometrically specified nuclear spins.

We show the effect of an applied electric field on the magnetization of an Fe ultrathin film. An electric double layer was formed at the interface between an ionic liquid and the Fe layer by the accumulation of ions caused by applying a gate voltage, and a large electric field was exerted on the Fe film surface. The saturation magnetization increased when the electron density at the Fe surface increased. A change in the saturation magnetization of ~50% was observed by applying a gate voltage of ±2 V.

We have investigated current-induced domain wall (DW) motion in a perpendicularly magnetized Co/Ni nanowire under in-plane (hard-axis) and perpendicular (easy-axis) external magnetic fields. The DW velocity was found to be almost independent of them in the range of ±50 Oe. The result shows that reliable device operation against an external magnetic field disturbance can be achieved using the present system.

Perpendicular magnetic anisotropy (PMA) in Co20Fe60B20 films depending on the adjacent layers of Ta, Ru, and MgO was studied for reduction of switching current density Jc0 in in-plane magnetic tunnel junctions (MTJs). A MgO layer reduces the out-of-plane saturation field (Hs) of in-plane easy axis Co20Fe60B20 films by inducing a strong PMA at the Co20Fe60B20/MgO interface. The PMA is not affected much by the crystallinity in Co20Fe60B20 films with different capping layers. MTJ with a MgO capping layer shows a lower Jc0 than that with a Ru capping layer, in accordance with the reduction of Hs.

The authors investigated tunnel magnetoresistance (TMR) properties in [CoFe/Pd]-multilayer/CoFeB/MgO/CoFeB/[Pd/CoFe]-multilayer magnetic tunnel junctions (MTJs) having two different Pd layer thicknesses. By reducing the Pd layer thickness from 1.2 to 0.2 nm, the TMR ratio was enhanced from 7 to 101% at the annealing temperature (Ta) of 300 °C. The thin Pd layers resulted in high residual B concentration in the CoFeB layer after high-Ta annealing and in the suppression of crystallization of the CoFeB layer from the fcc(111)-Pd layer side.

A compact ternary content-addressable memory (TCAM) cell of 3.15 µm2 with a 0.14 µm complementary metal oxide semiconductor process is realized by the use of nonvolatile magnetic tunnel junction (MTJ) devices with spin-injection write. This TCAM cell based on logic-in-memory architecture with nonvolatile MTJs needs no standby power, yet allows instant shut-down of the supply voltage without data backup to an external nonvolatile device.

Thermally activated longitudinal optical (LO) phonon scattering time (τthermal LO) of excited subbands in a 3.8 THz quantum cascade laser is studied. The active region used herein is based on a LO phonon depopulation scheme. A single plasmon waveguide was used for optical confinement. By calculating the temperature dependence of threshold current density (Jth) and comparing with the experiment, τthermal LO limiting the characteristic temperature of Jth is estimated: τthermal LO is 246 ns at 5 K, which rapidly decreases 15 ps when temperature rises up to 100 K.

Nonvolatile logic-in-memory architecture, where nonvolatile memory elements are distributed over a logic-circuit plane, is expected to realize both ultra-low-power and reduced interconnection delay. We have fabricated a nonvolatile full adder based on logic-in-memory architecture using magnetic tunnel junctions (MTJs) in combination with metal oxide semiconductor (MOS) transistors. Magnesium oxide (MgO) barrier MTJs are used to take advantage of their high tunnel magneto-resistance (TMR) ratio and spin-injection write capability. The MOS transistors are fabricated using a 0.18 µm complementary metal oxide semiconductor (CMOS) process. The basic operation of the full adder is confirmed.