W. J. Kong

Field-free spin Hall effect driven magnetization switching in Pd/Co/IrMn exchange coupling system

All electrical manipulation of magnetization is crucial and of great important for spintronics devices for the sake of high speed, reliable operation, and low power consumption. Recently, widespread interests have been aroused to manipulate perpendicular magnetization of a ferromagnetic layer using spin-orbit torque (SOT) without field. We report that a commonly used antiferromagnetic material IrMn can be a promising candidate as a functional layer to realize field-free magnetization switching driven by SOT in which IrMn is employed to act as both the source of effective exchange bias field and SOT source. The critical switching current density within our study is Jc = 2.2 × 107 A/cm2, which is the same magnitude as similar materials such as PtMn. A series of measurements based on anomalous Hall effect was systematically implemented to determine the magnetization switching mechanism. This study offers a possible route for IrMn application in similar structures.

Electrical control over perpendicular magnetization switching driven by spin-orbit torques

Flexible control of magnetization switching by electrical manners is crucial for applications of spin-orbitronics. Besides of a switching current that is parallel to an applied field, a bias current that is normal to the switching current is introduced to tune the magnitude of effective damping-like and field-like torques and further to electrically control magnetization switching. Symmetrical and asymmetrical control over the critical switching current by the bias current with opposite polarities is both realized in Pt/Co/MgO and

Polarization‐Mediated Thermal Stability of Metal/Oxide Heterointerface

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The unconventional electronic properties of multiwall carbon nanotubes

-Ta/CoFeB/MgO systems, respectively. This research not only identifies the influences of field-like and damping-like torques on switching process but also demonstrates an electrical method to control it.

Tuning the metal-insulator transition in NdNiO3 heterostructures via Fermi surface instability and spin fluctuations

A polarization-mediated heterointerface is designed to research the thermal stability of magnetic metal/oxide interfaces. Using polarization engineering, the thermal stability of the interface between BiFeO3 and CoFeB can be improved by about 100°C. This finding provides new insight into the chemistry of the metal/oxide heterointerface.

Tunneling anisotropic magnetoresistance in fully epitaxial magnetic tunnel junctions with different barriers

Abstract We have investigated the field and the bias-voltage dependencies of the electrical conductance, as well as the temperature dependence of the thermoelectric power of multiwall carbon nanotubes. Consistent picture has been obtained which indicates that electron–electron strong correlation is a major rhythm at low temperatures.

Study of spin-orbit torque induced magnetization switching in synthetic antiferromagnet with ultrathin Ta spacer layer

We employed in situ pulsed laser deposition (PLD) and angle-resolved photoemission spectroscopy (ARPES) to investigate the mechanism of the metal-insulator transition (MIT) in NdNiO3 (NNO) thin films, grown on NdGaO3(110) and LaAlO3(100) substrates. In the metallic phase, we observe three-dimensional hole and electron Fermi surface (FS) pockets formed from strongly renormalized bands with well-defined quasiparticles. Upon cooling across the MIT in NNO/NGO sample, the quasiparticles lose coherence via a spectral weight transfer from near the Fermi level to localized states forming at higher binding energies. In the case of NNO/LAO, the bands are apparently shifted upward with an additional holelike pocket forming at the corner of the Brillouin zone. We find that the renormalization effects are strongly anisotropic and are stronger in NNO/NGO than NNO/LAO. Our study reveals that substrate-induced strain tunes the crystal field splitting, which changes the FS properties, nesting conditions, and spin-fluctuation strength, and thereby controls the MIT via the formation of an electronic order parameter with QAF similar to (1/4,1/4,1/4 +/- delta).

Field-Free Programmable Spin Logics via Chirality-Reversible Spin-Orbit Torque Switching

We report the tunneling anisotropic magnetoresistance (TAMR) in fully epitaxial Fe/Barrier/Fe (001) magnetic tunnel junctions (MTJs) where the Barrier is annealed MgO, MgAlOx, MgO-MgAlOx, or as-grown MgO/MgAlOx. The TAMR was measured as the magnetization of Fe electrodes rotated from in-plane to out-of-plane. The angular dependence of TAMR for all samples exhibited superposed behavior of twofold and fourfold symmetries. The proportion of fourfold symmetry is larger in MTJs with MgO and MgO-MgAlOx than that in MTJs with MgAlOx and MgO/MgAlOx barriers. By characterizing inelastic electron tunneling spectroscopy in the antiparallel state and parallel conductance of the MTJs, we revealed diverse minority interfacial resonant states (IRSs) and different contributions from Δ1 and Δ5 symmetry states to the conductance in the MTJs. Our results illustrate that the minority IRS dominated by Δ5 symmetry can mix with majority Δ1 states and give rise to the enhanced fourfold symmetric angular dependence in MTJs with MgO and MgO-MgAlOx barriers.

Pressure-Induced Transition in Magnetoresistance of Single-Walled Carbon Nanotubes

Spin manipulation in magnetic materials based on spin-orbit torque gives rise to promising families of magnetic memory and logic devices. In the synthetic antiferromagnetic structure of CoFeB/Ta/CoFeB where both CoFeB layers exhibit perpendicular anisotropy, we study the magnetization switching process based on the mechanism of spin-orbit torque and interlayer exchange coupling mediated by a Ta layer. The magnetization switching trigged by in-plane current is achieved. Though the heavy metal Ta layer is ultrathin, the critical current density is 8 × 106–1 × 107 A/cm2 with a bias field of 5–10 mT. Meanwhile, the current induced anti-damping-like field and field-like field are determined by the harmonic lock-in technique. Harmonic results suggest that the generation efficiency of the field-like field is ∼1.24 times that of the anti-damping-like field. The effective spin Hall angle of a Ta layer is derived to be around −0.158. Finally, we examine the magnetic properties of CoFeB layers as a function of temperature which indicates that the magnetic properties of bottom and top CoFeB layers have a close correlation with the interface quality and growth order.Spin manipulation in magnetic materials based on spin-orbit torque gives rise to promising families of magnetic memory and logic devices. In the synthetic antiferromagnetic structure of CoFeB/Ta/CoFeB where both CoFeB layers exhibit perpendicular anisotropy, we study the magnetization switching process based on the mechanism of spin-orbit torque and interlayer exchange coupling mediated by a Ta layer. The magnetization switching trigged by in-plane current is achieved. Though the heavy metal Ta layer is ultrathin, the critical current density is 8 × 106–1 × 107 A/cm2 with a bias field of 5–10 mT. Meanwhile, the current induced anti-damping-like field and field-like field are determined by the harmonic lock-in technique. Harmonic results suggest that the generation efficiency of the field-like field is ∼1.24 times that of the anti-damping-like field. The effective spin Hall angle of a Ta layer is derived to be around −0.158. Finally, we examine the magnetic properties of CoFeB layers as a function of tempe...

Observation of a logarithmic temperature dependence of thermoelectric power in multiwall carbon nanotubes

Spin-orbit torque (SOT)-induced magnetization switching exhibits chirality (clockwise or counterclockwise), which offers the prospect of programmable spin-logic devices integrating nonvolatile spintronic memory cells with logic functions. Chirality is usually fixed by an applied or effective magnetic field in reported studies. Herein, utilizing an in-plane magnetic layer that is also switchable by SOT, the chirality of a perpendicular magnetic layer that is exchange-coupled with the in-plane layer can be reversed in a purely electrical way. In a single Hall bar device designed from this multilayer structure, three logic gates including AND, NAND, and NOT are reconfigured, which opens a gateway toward practical programmable spin-logic devices.