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The utilization of orbital transport provides a versatile and efficient spin manipulation mechanism. As interest in orbital-mediated spin manipulation grows, we face a new issue to identify the underlying physics that determines the efficiency of orbital torque (OT). In this study, we systematically investigate the variation of OT governed by orbital Rashba-Edelstein effect at the Cu/Oxide interface, as we change the Oxide material. We find that OT varies by a factor of ~2, depending on the Oxide. Our results suggest that the active electronic interatomic interaction (hopping) between Cu and oxygen atom is critical in determining OT. This also gives us an idea of what type of material factors is critical in forming a chiral orbital Rashba texture at the Cu/Oxide interface.

Phonons and magnons are engineered by periodic potential landscapes in phononic and magnonic crystals, and their combined studies may enable valley phonon transport tunable by the magnetic field. Through nonreciprocal surface acoustic wave transmission, we demonstrate valley-selective phonon-magnon scattering in magnetoelastic superlattices. The lattice symmetry and the out-of-plane magnetization component control the sign of nonreciprocity. The phonons in the valleys play a crucial role in generating nonreciprocal transmission by inducing circularly polarized strains that couple with the magnons. The transmission spectra show a nonreciprocity peak near a transmission gap, matching the phononic band structure. Our results open the way for manipulating valley phonon transport through periodically varying magnon-phonon coupling.

Electric-field controlled magnetization dynamics is an important integrant in low power spintronic devices. In this letter, we demonstrate electric-field induced parametric excitation for CoFeB/MgO junctions by using interfacial in-plane magnetic anisotropy. When the in-plane magnetic anisotropy and the external magnetic field are parallel to each other, magnons are efficiently excited by using electric-field induced parametric excitation. Its wavelength and wavenumber are tuned by changing input power and frequency of the applied voltage. A generalized phenomenological model is developed to explain the underlying role of the electric-field torque. Electrical excitation with no Joule heating offers a good opportunity for developing magnonic devices and exploring various nonlinear dynamics in magnetic systems., 10 pages, 5 figures, currently under review

We report chirality-induced current-in-plane magnetoresistance (CIP-MR) in chiral molecule/ferromagnetic metal bilayer at room temperature. The previously reported chiralityinduced current-perpendicular-to-plane magnetoresistance (CPP-MR) originates from the chiral induced spin-selectivity (CISS) effect that needs charge-current passing through the molecule. In contrast, the observed CIP-MR in the present study requires no bias charge current through the molecule. The temperature dependence of CIP-MR suggests thermally induced spin-polarization in the chiral molecules is the key for the observed MR., 11 pages, 4 figures

On-demand magnonic nanochannels are achieved by modulation of voltage-controlled magnetic anisotropy in CoFeB/MgO heterostructure., Development of energy-efficient on-demand magnonic nanochannels (MNCs) can revolutionize on-chip data communication and processing. We have developed a dynamic MNC array by periodically tailoring perpendicular magnetic anisotropy using the electric field. Brillouin light scattering spectroscopy is used to probe the spin wave (SW) dispersion of MNCs formed by applying a static electric field at the CoFeB/MgO interface through the one-dimensional stripe-like array of indium tin oxide electrodes placed on top of Ta/CoFeB/MgO/Al2O3 heterostructures. Magnonic bands, consisting of two SW frequency modes, appear with a bandgap under the application of moderate gate voltage, which can be switched off by withdrawing the voltage. The experimental results are reproduced by plane wave method–based numerical calculations, and simulated SW mode profiles show propagating SWs through nanochannels with different magnetic properties. The anticrossing between these two modes gives rise to the observed magnonic bandgap.

Efficient spin/charge interconversion is desired to develop innovative spin-based devices. So far, the interconversion has been performed by using heavy atomic elements, strong spin-orbit interaction of which realizes the interconversion through the spin Hall effect and the Edelstein effect. We demonstrate highly efficient charge-to-spin conversion in a ferromagnetic metal/Cu/Al2O3 trilayers, which do not contain any heavy element. The resulting spin torque efficiency is higher than those of conventional spin Hall and Rashba systems consisting of heavy elements such as Pt and Bi. Our experimental results qualitatively deviate from typical behaviors arising from spin transport. However, they are surprisingly consistent with the behaviors arising from the orbital transport. Our results thus demonstrate a new direction for efficient charge-to-spin conversion through the orbital transport.

Oxide interfaces are a source of spin-orbit coupling which can lead to novel spin-to-charge conversion effects. In this work the contribution of the Bi$_2$O$_3$ interface to the anomalous Hall effect of Co is experimentally studied in Co/Bi$_2$O$_3$ bilayers. We evidence a variation of 40% in the AHE of Co when a Bi$_2$O$_3$ capping layer is added to the ferromagnet. This strong variation is attributed to an additional source of asymmetric transport in Co/Bi$_2$O$_3$ bilayers that originates from the Co/Bi$_2$O$_3$ interface and contributes to the skew scattering., Comment: 7 pages, 4 figures

We have experimentally elucidated the correlation between inverse and direct Edelstein Effects (EEs) at Bi2O3/Cu interface by means of spin absorption method using lateral spin valve structure. The conversion coefficient {\lambda} for the inverse EE is determined by the electron momentum scattering time in the interface, whereas the coefficient q for the direct EE is by the spin ejection time from the interface. For the Bi2O3/Cu interface, the spin ejection time was estimated to be ~ 53 fs and the momentum scattering time ~ 13 fs at room temperature, both of which contribute to the total momentum relaxation time that defines the resistivity of the interface. The effective spin Hall angle for the Bi2O3/Cu interface amounts to ~ 10% which is comparable to commonly used spin Hall material such as platinum. Interesting to note is that the experimentally obtained Edelstein resistances given by the output voltage divided by the injection current for direct and inverse effects are the same. Analysis based on our phenomenological model reveals that the larger the momentum scattering time, the more efficient direct EE; and the smaller spin ejection time, the more efficient inverse EE.

We demonstrate a large angular dependence of magnetization dynamics in Ni80Fe20 nano-cross arrays of varying sizes. By subtle variation of the azimuthal angle of an in-plane bias magnetic field, the spin configuration and the ensuing spin-wave dynamics, including mode softening, mode splitting, mode crossover and mode merging, can be drastically varied to the extent that a frequency minimum corresponding to mode softening converts to a mode crossover, various mode splitting and mode crossover disappear and additional mode splitting appears. Numerically simulated spin-wave spectra and phase profiles revealed the nature of various spin-wave modes and the origin of above variation of the dynamics with bias-field angle. All of these above observations are further modified with the variation of dimensions of the nano-cross. The numerically calculated magnetostatic field distributions further supports the variation of dynamics with bias-field angle. These results open a new avenue for engineering the nano-cross based magnetic devices such as magnetic storage, spin-wave logic and on-chip data communication devices.

Active control of spin-wave dynamics is demonstrated using broadband ferromagnetic resonance in two-dimensional Ni80Fe20 antidot lattices arranged in hexagonal lattice with fixed lattice constant but varying antidot diameter. A strong modification in the spin-wave spectra is obtained with the variation in the antidot diameter as well as with the strength and orientation of the bias magnetic field. A broad band of modes is observed for the lattice with higher antidot diameter which decreases systematically as the antidot diameter is reduced. A crossover between the higher frequency branches is achieved in lattices with higher antidot diameter. In addition, the spin-wave modes in all lattices show a strong six-fold anisotropic behaviour due to the variation of internal field distribution as a function of the bias-field orientation. A mode hopping-like behavior is observed in the angular dispersions of spin-wave spectra for samples having intermediate hole diameters. Micromagnetic simulations qualitatively reproduce the experimentally observed spin-wave modes and the simulated mode profiles reveal the presence of extended and quantized standing spin-wave modes in these lattices. These observations are significant for large tunability and anisotropic propagation of spin waves in GHz frequency magnetic devices.

Devices based on a pure spin current (a flow of spin angular momentum) have been attracting increasing attention as key ingredients for low-dissipation electronics. To integrate such spintronics devices into charge-based technologies, an electric detection of spin current is essential. Inverse spin Hall effect converts a spin current into an electric voltage through spin-orbit coupling. Noble metals such as Pt and Pd, and also Cu-based alloys, owing to the large direct spin Hall effect, have been regarded as potential materials for a spin-current injector. Those materials, however, are not promising as a spin-current detector based on inverse spin Hall effect. Their spin Hall resistivity rho_SH, representing the performance as a detector, is not large enough mainly due to their low charge resistivity. Here we demonstrate that heavy transition metal oxides can overcome such limitations inherent to metal-based spintronics materials. A binary 5d transition metal oxide IrO2, owing to its large resistivity as well as a large spin-orbit coupling associated with 5d character of conduction electrons, was found to show a gigantic rho_SH ~ 38 microohm cm at room temperature, one order of magnitude larger than those of noble metals and Cu-based alloys and even comparable to those of atomic layer thin film of W and Ta.

The spin Hall effect (SHE) is one of the important phenomena in spintronics since it enables to create spin currents in non-magnetic materials without using a ferromagnet. Recently-reported large SHEs in Pt and Au have triggered the search for a larger SHE in metallic devices. The mechanism of the large SHEs, however, have not been figured out yet ; whether it is intrinsic or extrinsic, if it is extrinsic whether it stems from the skew scattering mechanism or the side jump one. In this work, we focus on the extrinsic SHE. By adding Ir impurity into pure Cu, we have studied the impurity concentration dependence of the SHE in CuIr. We have used the lateral spin valve structure which consists of two Py wires and a CuIr middle wire.This device allows to estimate precisely how much spin currents are injected into CuIr. By flowing electric current from Py to one of the Cu electrodes, pure spin currents are injected into the CuIr middle wire and we are able to measure the inverse SHE. No SHE has been observed when there is no Ir impurity. With increasing the Ir impurity, however, the SH resistivity increases linearly with the resistivity of CuIr. This linear dependence strongly indicates that the SHE in CuIr is due to the skew scattering mechanism. From the slope of the SHE resistivity vs CuIr resistivity curve, it turns out that the SH angle in this system is 1.5%, which is consistent with the previous anomalous Hall effect measurement in CuMnIr.

We present experimental results which show that doping Cu with (nonmagnetic) 6d impurities can induce a very large Spin Hall Effect. The Spin Hall conductivity can exceed 10^7 Ohm^(-1)m^(-1), to be compared to 10^4-10^6 Ohm^(-1)m^(-1) in Pt or Au (Kimura et al, PRL 2007 ; Seki et al, Nature Materials ; 2008), 10^3 Ohm^(-1)m^(-1) in Al (Valenzuela and Tinkham, Nature 2006) or 1 Ohm^(-1)m^(-1) in InGaAs (Kato et al, Science 2004). Resonant skew scattering on spin-orbit split impurity states explains the large value of the SHE induced by nonmagnetic impurities like Ir, Ta, Lu or Sb. It also explains that the different signs of the SHE we observe at the beginning (Lu) and end (Ir) of the 5d series are related to the position of the resonant 5d states with respect to the Fermi level. We will present a theoretical model of resonant skew scattering accounting for our results and discuss the advantage of resonant scattering on other mechanisms. An extension to resonant side-jump scattering will be also presented.

We investigate the dynamics of a magnetic vortex driven by spin-transfer torque due to spin current in the adiabatic case. The vortex core represented by collective coordinate experiences a transverse force proportional to the product of spin current and gyrovector, which can be interpreted as the geometric force determined by topological charges. We show that this force is just a reaction force of Lorentz-type force from the spin current of conduction electrons. Based on our analyses, we propose analytically and numerically a possible experiment to check the vortex displacement by spin current in the case of single magnetic nanodot.