The phenomena based on spin-orbit interaction in heavy metal/ferromagnet/oxide structures have been investigated extensively due to their applicability to the manipulation of the magnetization direction via the in-plane current. This implies the existence of an inverse effect, in which the conductivity in such structures should depend on the magnetization orientation. In this work, we report a systematic study of the magnetoresistance (MR) of W/CoFeB/MgO structures and its correlation with the current-induced torque to the magnetization. We observe that the MR is independent of the angle between the magnetization and current direction but is determined by the relative magnetization orientation with respect to the spin direction accumulated by the spin Hall effect, for which the symmetry is identical to that of so-called the spin Hall magnetoresistance. The MR of ~1% in W/CoFeB/MgO samples is considerably larger than those in other structures of Ta/CoFeB/MgO or Pt/Co/AlOx, which indicates a larger spin Hall angle of W. Moreover, the similar W thickness dependence of the MR and the current-induced magnetization switching efficiency demonstrates that MR in a non-magnet/ferromagnet structure can be utilized to understand other closely correlated spin-orbit coupling effects such as the inverse spin Hall effect or the spin-orbit spin transfer torques.

Interfacial perpendicular magnetic anisotropy (PMA) in CoFeB/MgO structures was investigated and found to be critically relied on underlayer material and annealing temperature. With Ta or Hf underlayer, clear PMA is observed in as-deposited samples while no PMA was shown in those with Pt or Pd. This may be attributed to smaller saturation magnetization of the films with Ta or Hf underlayer, which makes the PMA of CoFeB/MgO interface dominates over demagnetization field. On the contrary, samples with Pt or Pd demonstrate PMA only after annealing, which might be due to the CoPt (or CoPd) alloy formation that enhances PMA.

An ultrafast spin demagnetization process of an amorphous Tb35Fe65 alloy film has been investigated by means of an all-optical pump-probe technique. Interestingly, steplike demagnetization on a subpicosecond time scale is observed before a much slower change on a time scale of tens of picoseconds. The steplike demagnetization at the subpicosecond scale is explained by the extended three-temperature model considering the interaction between a nonthermal electron and a spin system. The characteristic of subpicosecond demagnetization of TbFe alloy film is expected to be very useful in the manipulation of the spin state in ultrafast regime.

The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers. It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE. Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously. The experimental observation of the improvement of thermoelectric properties may pave the way for the realization of magnetic-(or spin-) based thermoelectric devices.

We have investigated the ultrafast magnetization dynamics of L10-ordered Fe50Pt50 thin film by means of a time-resolved magneto-optical Kerr effect measurement. We have found a high Gilbert damping value of α∼0.26, together with a very high precession frequency of f∼85 GHz and the shortest relaxation characteristic time of τ∼6.5 ps ever reported. We believe that L10-ordered FePt film with the unique property of a very high precession frequency and the shortest relaxation time will be very useful for the realization of picosecond spin switching.

Seebeck coefficient S, high electrical conductivity σ, and low thermal conductivity κ, which are normally expressed by the thermoelectric figure of merit, ZT = σS 2 T/κ, where T is the absolute temperature. [1][2][3][4][5] To improve ZT, research on various materials has been performed, where κ is minimized by phonon engineering, [3] and the power factor (σS 2 ) is enhanced by modification of the band structure. [4] As an alternative and novel route to improve the thermoelectric efficiency, several interesting approaches, such as the spin Seebeck, anisotropic Seebeck, electrolyte Seebeck, and photo Seebeck effects, have been proposed recently. [6][7][8][9] Among these approaches, the spin Seebeck effect [9] has especially attracted attention with regard to thermoelectrics in various magnetic systems (or spin thermoelectrics) as a new strategy for thermoelectric energy conversion [10][11][12][13][14] and as a spin current source in spintronic devices. [15][16][17][18][19][20] Although the spin Seebeck effect is fascinating as the spin counterpart of the Seebeck effect, practical thermoelectric power generation using spin Seebeck effect is yet to be developed. Therefore, obviously, the most critical aspect of spin thermoelectrics for practical applications is to increase the efficiency of energy conversion, which has been engineered with regard to thermal conductivity, [21,22] band gap of the semiconductor, [16,23,24] and the spin Hall angle (θ SH ), [13] among others. In addition to these attempts, a spin thermopile consisting of wire elements of a ferromagnetic (FM)/electrode bilayer can increase the overall voltage by alternating the polarity of each element in a zigzag structure, [13,[25][26][27] as magnetic materials certainly can gain benefits from tunability of the magnetic direction and a nanoscale modulating structure. [28][29][30] Previously, spin thermopiles utilizing the anomalous Nernst effect (ANE) alone showed enhanced signals with alternating signs of ANE coefficients (C ANE ) or with an alternating magnetic direction. [27] However, its operating magnetic field is somewhat large, on the order of kOe, and the signal shows hysteretic behavior when subjected to coercive-field modulation to control the magnetic direction. It has also been reported that thermopiles with the inverse spin Hall effect (ISHE) can be fabricated The thermoelectric effect in various magnetic systems, in which electric voltage is generated by a spin current, has attracted much interest owing to its potential applications in energy harvesting, but its power generation capability has to be improved further for actual applications. In this study, the first instance of the formation of a spin thermopile via a simplified and straightforward method which utilizes two distinct characteristics of antiferromagnetic IrMn is reported: the inverse spin Hall effect and the exchange bias. The former allows the IrMn efficiently to convert the thermally induced spin current into a measurable voltage, and the latter can be used to control the ...

The relative contribution of spin pumping and spin rectification from the ferromagnetic resonance of CoFeB/non-magnetic bilayers was investigated as a function of non-magnetic electrode resistance. Samples with highly resistive electrodes of Ta or Ti exhibit a stronger spin rectification signal, which may result in over-(or under-)estimation of the spin Hall angle of the materials, while those with low resistive electrodes of Pt or Pd show the domination of the inverse spin Hall effect from spin pumping. By comparison with samples of single FM layer and an inverted structure, we provide a proper analysis method to extract spin pumping contribution.

Stochastic behavior of nucleationprocess during magnetization reversalon a nanoscale in a nanogranularCoCrPt alloy film is directly observedutilizing magnetic soft X‐raytransmission microscopy, whichprovides a spatial resolution of 15 nm.Thermal fluctuations in the orientationof the magnetic moments of the grainsplay a dominant role for the stochasticnature of domain nucleation in this system.