Kangkang Meng

Anomalous Hall effect and spin-orbit torques in MnGa/IrMn films: Modification from strong spin Hall effect of the antiferromagnet

We report systematic measurements of anomalous Hall effect (AHE) and spin-orbit torques (SOTs) in MnGa/IrMn films, in which a single

Spin Hall magnetoresistance in an antiferromagnetic magnetoelectric Cr2O3/heavy-metal W heterostructure

L{1}_{0}\text{\ensuremath{-}}\mathrm{MnGa}

Modulated switching current density and spin-orbit torques in MnGa/Ta films with inserting ferromagnetic layers

epitaxial layer reveals obvious orbital two-channel Kondo (2CK) effect. As increasing the thickness of the antiferromagnet IrMn, the strong spin Hall effect (SHE) has gradually suppressed the orbital 2CK effect and modified the AHE of MnGa. A scaling involving multiple competing scattering mechanisms has been used to distinguish different contributions to the modified AHE. Finally, the sizeable SOT in the MnGa/IrMn films induced by the strong SHE of IrMn have been investigated. The IrMn layer also supplies an in-plane exchange bias field and enables nearly field-free magnetization reversal.

Enhanced spin-orbit torques in MnAl/Ta films with improving chemical ordering

The spin Hall magnetoresistance (SMR) effect is studied in a magnetoelectric Cr2O3/heavy-metal W heterostructure. The Cr2O3 film is confirmed as the α-phase, and its Neel temperature is determined. A clear SMR behavior is observed at the interface of Cr2O3/W. A nearly 0.1% SMR ratio is achieved under a magnetic field of 9 T, which is larger than the reported value in the SrMnO3/Pt structure. A systematic study on the variations of SMR as functions of the magnetic field and its angle is performed. Our results indicate that the antiferromagnetic magnetoelectric Cr2O3/W structure has a promising prospect application in future spintronic devices.

Hybrid magnetoresistance in Pt-based multilayers: Effect originated from strong interfacial spin-orbit coupling

We report modulated switching current density and spin-orbit torques (SOT) in MnGa/Ta films with inserting very thin Co2FeAl and Co layers. Ferromagnetic coupling has been found in MnGa/Co2FeAl/Ta, resulting in a decreased effective anisotropy field. On the contrary, in MnGa/Co/Ta, antiferromagnetic coupling plays a dominant role. The switching current density Jc in MnGa/Ta is 8.5 × 107 A/cm2. After inserting 0.8-nm-thick Co2FeAl and Co, theJc becomes 5 × 107 A/cm2 and 9 × 107 A/cm2, respectively. By performing adiabatic harmonic Hall voltage measurements, it is demonstrated that the inserted Co2FeAl layer has mainly enhanced the field-like torques, while in MnGa/Co/Ta the damping-like torques have been enhanced. Finally, the enhanced spin Hall effect (SHE) has also been studied using the spin Hall magnetoresistance measurement. The modulated Jc and SOT are ascribed to the combination of magnetic coupling, Rashba effect and SHE at the interfaces.

The dominancy of damping like torque for the current induced magnetization switching in Pt/Co/W multilayers

We report the enhancement of spin-orbit torques (SOT) in MnAl/Ta films with improving chemical ordering through annealing. The switching current density is increased due to enhanced saturation magnetization MS and effective anisotropy field HK after annealing. Using harmonic measurements, we have found that both dampling-like effective field HD and field-like effective field HF were increased in the temperature range of 50 to 300 K, and the annealing has also enhanced the value of the spin Hall angle. The improved chemical ordering is considered to have enhanced the interfacial spin transparency and the transmitting of the spin current in the MnAl layer. The results suggest that MnAl films with high bulk perpendicular magnetic anisotropy are ideal for a systematic examination of SOT, in which the related magnetic and transport behaviors can be controllably varied with thermally tuned chemical ordering.

Negative spin Hall magnetoresistance in antiferromagnetic Cr2O3/Ta bilayer at low temperature region

The hybrid magnetoresistance (MR) behaviors in Pt/Co90Fe10/Pt, Mn1.5Ga/Pt and Mn1.5Ga/Pt/Co90Fe10/Pt multilayers have been investigated. Both planer Hall effect (PHE) and angle-dependent MR in Pt/Co90Fe10/Pt revealed the combination of spin Hall MR (SMR) and normal anisotropic MR (AMR), indicating the large contribution of strong spin-orbit coupling (SOC) at the interfaces. When Pt contacted with perpendicular magnetic anisotropy (PMA) metal Mn1.5Ga, the strong interfacial SOC modified the effective anomalous Hall effect. The MR in Mn1.5Ga/Pt/Co90Fe10/Pt is not a simple combination of SMR and AMR, but ascribed to the complicated domain wall scattering and strong interfacial SOC when Pt is sandwiched by the in-plane magnetized Co90Fe10 and the PMA Mn1.5Ga.

Heteroepitaxial Pb0.9Sr0.1TiO3/Bi0.9La0.1FeO3/Pb0.9Sr0.1TiO3 multiferroic structure: an effective way to improve the electrical, ferroelectric and magnetic performance

Two classes of spin-orbit coupling (SOC) mechanisms have been considered as candidate sources for the spin orbit torque (SOT): the spin Hall Effect (SHE) in heavy metals with strong SOC and the Rashba effect arising from broken inversion symmetry at material surfaces and interfaces. In this work, we have investigated the SOT in perpendicularly magnetized Pt/Co/W films, which is compared with the results in Pt/Co/AlOx films. Theoretically, in the case of the asymmetric structure of trilayers with opposite sign of spin Hall angle, both damping like torque and field like torque due to the SHE and the Rashba effect will be enhanced. Using the harmonic measurements, we have characterized the effective fields corresponding to the damping like torque and the field like torque, but we have found the dominancy of damping like torque in the Pt/Co/W films. It is much different from the results in the Pt/Co/AlOx films, in which both the damping like torque and the field like torque are strong.

In-plane electric field controlled ferromagnetism and anisotropic magnetoresistance in an LSMO/PMN-PT heterostructure

We investigate the observation of negative spin Hall magnetoresistance (SMR) in antiferromagnetic Cr2O3/Ta bilayers at low temperature. The sign of the SMR signals is changed from positive to negative monotonously from 300 K to 50 K. The change of the signs for SMR is related with the competitions between the surface ferromagnetism and bulky antiferromagnetic of Cr2O3. The surface magnetizations of Cr2O3 (0001) is considered to be dominated at higher temperature, while the bulky antiferromagnetics gets to be robust with decreasing of temperature. The slopes of the abnormal Hall curves coincide with the signs of SMR, confirming variational interface magnetism of Cr2O3 at different temperature. From the observed SMR ratio under 3 T, the spin mixing conductance at Cr2O3/Ta interface is estimated to be 1.12*10^14 (ohm^-1*m^-2), which is comparable to that of YIG/Pt structures and our early results of Cr2O3/W. (Appl. Phys. Lett. 110, 262401 (2017))

Modulated spin orbit torque in a Pt/Co/Pt/YIG multilayer by nonequilibrium proximity effect

AbstractsA ferroelectric/multiferroic structure composed of (Pb0.9Sr0.1)TiO3 (PST) and (Bi0.9La0.1)FeO3 (BLF) was heteroepitaxially deposited on a LaNiO3 buffered (001) SrTiO3 substrate by pulse laser deposition. Interestingly, the PST layer was acting as a buffering layer between BLF and electrode to suppress the migration of free carries in the heterostructure. A well-grown crystalline dense structure was observed from the surface morphology of PST/BLF/PST heterostructure. Moreover, the PST/BLF/PST trilayer exhibited improved ferroelectric and dielectric behaviors, together with two orders of magnitude lower leakage current and higher dielectric constant. Our result indicate that the multiferroic PST/BLF/PST heterostructure may have a promising application for the future high-density memory.