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Spatial symmetry of spin pumping and inverse spin Hall effect in the Pt/YIG system
The spatial symmetry of spin pumping, i.e., the voltage amplitude of the inverse spin Hall effect varying with the orientation of static magnetization and the polarization direction of a dynamic magnetic field, has been systematically studied both theoretically and experimentally. This symmetry is quite important because it is the unique foundation and criterion for identifying the spin pumping signal from other contributions to the voltage and for unveiling the underlying physics of spin pumping and pure spin current. As a straightforward proof, we found the spin mixing conductance to be out-of-plane anisotropic, which comes from an elaborate study of the symmetry of a Pt/YIG bilayer after examining every effect that may contribute to the angular dependence of spin pumping; the spin Hall angle, however, is a constant that is independent of the polarization direction of the spin current.
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Magnetoresistance Amplification Effect in Silicon Transistor Device
Large magnetoresistance discovered in nonmagnetic semiconductors offers an alternative route to renew magnetoelectronics without ferromagnets. However, it is still a great challenge to retain such large magnetoresistance under low magnetic fields. In this work, analogous to current amplification in the transistor, a magnetoresistance amplification effect is proposed in silicon transistor device, where the device current is significantly controlled by magnetic-field-manipulated coupling of two p-n junctions in transistor. As a direct consequence, large magnetoresistance of 50 000% with high sensitivity of 50% Oe(-1) is yielded at magnetic field of only 0.1 T. The results not only provide here a new proposal compatible with current semiconductor technology to achieve large magntoresistance at low magnetic field, but also realize magnetic-field-manipulated transistor, which is a step for magnetoelectronics.
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In-plane Isotropic Microwave Performance of CoZr Trilayer in GHz Range
In this work, we investigate the high frequency performance of Co90Zr10/SiO2/Co90Zr10 trilayers. It is demonstrated that the in-plane isotropic microwave performance is theoretically derived from the solution of the Landau-Lifshitz-Gilbert equation and experimentally achieved in that sandwich structured film. The isotropic microwave performance can be tuned to higher resonance frequency up to 5.3 GHz by employing the oblique deposition technique.
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A non-volatile four-state magnetic memory in a Co/(011)Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure
A non-volatile four-state magnetic memory is achieved in a Co/(011)Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure. The in-plane magnetization of ferromagnetic Co film in the heterostructure can be controlled both electrically and magnetically. Electric field mediated magnetism is caused by piezostrain effect, which displays a stable non-volatile remnant magnetization vs electric field looplike behavior. In-plane strain-electric field (S-E) behavior under different temperatures reveals a nonvolatile strain switching effect, which is responsible for the non-volatile remnant magnetization switching through piezostrain mediated magnetoelectric effect. Further investigations on temperature dependence of S-E behavior suggest that the absent of the second non-180 domain switching may be responsible for the asymmetry in strain curves that causes the non-volatile strain switching, and therefore causes the non-volatile remanent magnetization switching, which is crucial for the four-state magnetoelectric memory.
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Metallic Ni3N nanosheets with exposed active surface sites for efficient hydrogen evolution
Ni-Based catalysts have been considered as promising non-noble-metal hydrogen evolution reaction (HER) electrocatalysts for future clean energy devices. Here, atomically thin metallic Ni3N nanosheets are fabricated as the hydrogen evolution cathode, which exhibit remarkable HER activity close to that of a commercial Pt/C electrode. The Ni3N nanosheet catalyst shows an electrocatalytic current density of 100 mA cm2 at a low overpotential of 100 mV vs. RHE, a high exchange current density of 0.32 mA cm2, a Tafel slope of 59.79 mV dec1 and remarkable durability (little activity loss >5000 cycles) in acidic media as well as high HER activity in neutral and alkaline media. Through systematic theoretical calculations, the active surface sites of the Ni3N nanosheets are explicitly identified. The Ni atoms accompanied by surrounding N atoms on the N–Ni surface demonstrate a small DGH* of 0.065 eV due to the Ni–N co-effect, which act as the most active HER sites. This finding broadens our vision to realize the HER activity of 2D metallic electrocatalysts and paves the way for exciting opportunities in exploring and optimizing advanced catalysts for future energy production.
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Theoretical Prediction of Carrier Mobility in Few-Layer BC2N
An ideal semiconducting material should simultaneously hold a considerable direct band gap and a high carrier mobility. A 2D planar compound consisting of zigzag chains of C−C and B−N atoms, denoted as BC2N, would be a good candidate. It has a direct band gap of 2 eV, which can be further tuned by changing the layer number. At the same time, our first-principles calculations show that few-layer BC2N possesses a high carrier mobility. The carrier mobility of around one million sqaure centimeters per volt-second is obtained at its three-layer. As our study demonstrated, few-layer BC2N has potential applications in nanoelectronics and optoelectronics.
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Single-spin manipulation by electric fields and adsorption of molecules
Performing ab initio calculations, we reveal that the magnetic anisotropy (MA) and the spin direction of a single adatom can be manipulated with a combination of electric fields and adsorption of molecules. Choosing the Fe adatom on the Cu2N/Cu(001) surface as a typical model system, we show that the MA of the pristine Fe adatom and the Fe adatom with an additional H or F atom adsorption remarkably changes by applying an external electric field. Moreover, we show that the F adsorption leads to the spin-reorientation transition of the Fe adatom from in plane to out of plane. Controlling the magnetization dynamics of a single magnetic adatom by molecule adsorption is demonstrated.
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Structural Phase Transition Effect on Resistive Switching Behavior of MoS2-Polyvinylpyrrolidone Nanocomposites Films for Flexible Memory Devices
The 2H phase and 1T phase coexisting in the same molybdenum disulfi de (MoS2) nanosheets can infl uence the electronic properties of the materials. The 1T phase of MoS2 is introduced into the 2H-MoS2 nanosheets by two-step hydrothermal synthetic methods. Two types of nonvolatile memory effects, namely write-once read-many times memory and rewritable memory effect, are observed in the fl exible memory devices with the confi guration of Al/1T@2H-MoS2-polyvinylpyrrolidone (PVP)/ indium tin oxide (ITO)/polyethylene terephthalate (PET) and Al/2H-MoS2-PVP/ ITO/PET, respectively. It is observed that structural phase transition in MoS2 nanosheets plays an important role on the resistive switching behaviors of the MoS2 - based device. It is hoped that our results can offer a general route for the preparation of various promising nanocomposites based on 2D nanosheets of layered transition metal dichalcogenides for fabricating the high performance and fl exible nonvolatile memory devices through regulating the phase structure in the 2D nanosheets.
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A Large Magnetoresistance Effect in p–n Junction Devices by the Space-Charge Effect
The finding of an extremely large magnetoresistance effect on silicon based p–n junction with vertical geometry over a wide range of temperatures and magnetic fi elds is reported. A 2500% magnetoresistance ratio of the Si p–n junction is observed at room temperature with a magnetic fi eld of 5 T and the applied bias voltage of only 6 V, while a magnetoresistance ratio of 25 000% is achieved at 100 K. The current-voltage ( I–V ) behaviors under various external magnetic fi elds obey an exponential relationship, and the magnetoresistance effect is signifi cantly enhanced by both contributions of the electric fi eld inhomogeneity and carrier concentrations variation. Theoretical analysis using classical p–n junction transport equation is adapted to describe the I–V curves of the p–n junction at different magnetic fi elds and reveals that the large magnetoresistance effect origins from a change of space-charge region in the p–n junction induced by external magnetic fi eld. The results indicate that the conventional p–n junction is proposed to be used as a multifunctional material based on the interplay between electronic and magnetic response, which is signifi cant for future magneto-electronics in the semiconductor industry.
