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Non-reciprocal charge transport that is strongly associated with the structural or magnetic chirality of the quantum materials system is one of the most exotic properties of condensed matter physics. Here, using magnetic alloys film Pt2MnGe, we have realized the large non-reciprocal charge transport up to room temperature, which roots in the organic combination of chirality dependent carrier scattering and special magnetic configurations. In this framework, the conduction electrons are scattered asymmetrically by the emerging non-zero vector spin chirality under in-plane magnetic field, resulting in robust non-reciprocal response. More astonishingly, the vector spin chirality in Pt2MnGe film can be reversed by a spin-polarized current through spin Hall effect in a junction with Pt layer. Our work resolves the general limitation of non-reciprocal charge transport to cryogenic temperatures, and paves the way for extending its applications in the emerging field of chiral spintronics.

Nonreciprocal charge transport, which is frequently termed as electrical magnetochiral anisotropy (EMCA) in chiral conductors, touches the most important elements of modern condensed matter physics. Here, we have investigated the EMCA in Pt/PtMnGa (PMG) bilayers with the assitance of nonequilibrium fluctuation theorems. Large EMCA in the Pt/PMG bilayers can be attributed to nonreciprocal response of an interface-driven chiral transport channel. Due to the presence of large charge fluctuations for small current region, higher order EMCA coefficients should be added and they are all functions of current. A combination of asymmetrical electron scattering and spin-dependent scattering furnish the PMG thickness dependent chiral transport behaviors in Pt/PMG bilayers. The dramatically enhanced anomalous Hall angle of PMG further demonstrates the modified surface state properties by strong spin-orbit coupling.

We report spin-orbit torques (SOT) in L10-ordered perpendicularly magnetized FePt single layer, which is significantly influenced by disorder. Recently, self-induced SOT in L10-FePt single layer has been investigated, which is ascribed to the composition gradient along the film normal direction. However, the determined mechanisms for magnetization switching have not been fully studied. With varying growth temperatures, we have prepared FePt single layers with same thickness (3 nm) but with different disordering. We have found that nearly full magnetization switching only happens in more disordered films, and the magnetization switching ratio becomes smaller as increasing L10 ordering. The method for deriving effective spin torque fields in the previous studies cannot fully explain the spin current generation and self-induced SOT in L10-FePt single layer. Combined with Magneto-Optical Kerr Effect microscopy and anomalous Hall effect measurements, we concluded that the disorder should determine the formation of domain walls, as well as the spin current generation., Comment: arXiv admin note: text overlap with arXiv:1411.3249 by other authors

Spin Hall magnetoresistance (SMR) and magnon excitation magnetoresistance (MMR) that all generate via the spin Hall effect and inverse spin Hall effect in a nonmagnetic material are always related to each other. However, the influence of magnon excitation for SMR is often overlooked due to the negligible MMR. Here, we investigate the SMR in Pt/Y3Fe5O12 (YIG) bilayers from 5 to 300K, in which the YIG are treated after Ar+-ion milling. The SMR in the treated device is smaller than in the non-treated. According to theoretical simulation, we attribute this phenomenon to the reduction of the interfacial spin-mixing conductance at the treated Pt/YIG interface induced by the magnon suppression. Our experimental results point out that the SMR and the MMR are inter-connected, and the former could be modulated via magnon excitation. Our findings provide a new approach for separating and clarifying the underlying mechanisms.

The spin currents generated by spin-orbit coupling (SOC) in the nonmagnetic metal layer or at the interface with broken inversion symmetry are of particular interest and importance. Here, we have explored the spin current generation mechanisms through the spin-orbit torques (SOTs) measurements in the Ru/Fe heterostructures with weak perpendicular magnetic anisotropy (PMA). Although the spin Hall angle (SHA) of Ru is smaller than that in Pt, Ta or W, reversible SOT in Ru/Fe heterostructures can still be realized. Through non-adiabatic harmonic Hall voltage measurements and macrospin simulation, the effective SHA in Ru/Fe heterostructures is compared with Pt. Moreover, we also explore that the spin current driven by interface strongly depends on the electrical conductivities. Our results suggest a new method for efficiently generating finite spin currents in ferromagnet/nonmagnetic metal bilayers, which establishes new opportunities for fundamental study of spin dynamics and transport in ferromagnetic systems.

In this work, the BiFeO3 (BFO)/SrRuO3 (SRO) heterostructure was fabricated and the anomalous Hall effect (AHE) was investigated the in BFO/SRO. It is found the nonmonotonic anomalous Hall resistivity behavior in BFO/SRO is originated from the inhomogeneous SRO layer instead of the topological Hall effect. It is surprised that the AHE in BFO/SRO structure can be manipulated by ferroelectric polarization of BFO. Moreover, an inhomogeneous phenomenological model has been applied on those structure. Furthermore, the modification of band structure in SRO under ferroelectric polarization was discussed by first principle calculation. The ferroelectric-manipulated AHE suggests a new pathway to realize nonvolatile, reversible and low energy-consuming voltage-controlled spintronic devices.

Multiferroic tunnel junctions (MFTJs) have already been proved to be promising candidates for application in spintronics devices. The coupling between tunnel magnetoresistance (TMR) and tunnel electroresistance (TER) in MFTJs can provide four distinct resistive states in a single memory cell. Here we show that in an all-oxide asymmetric MFTJ of La0.7Sr0.3MnO3 /PbZr0.2Ti0.8O3 /La0.7Te0.3MnO3 (LSMO/PZT/LTMO) with p-type and n-type electrodes, the intrinsic rectification is observed and can be modified by the ferroelectric polarization of PZT. Owing to the combined TMR, TER and diode effects, two different groups of four resistive states under opposite reading biases are performed. With two parallel asymmetric junctions and the appropriate series resistance, the coexistence of logic units and quaternary memory cells can be realized in the same array devices. The asymmetric MFTJ structure enables more possibilities for designing next generation of multi-states memory and logical devices with higher storage density, lower energy consumption and significantly increased integration level.

In the last few years, some ideas of electric manipulations in ferromagnetic heterostructures have been proposed for developing next generation spintronic devices. Among them, the magnetization switching driven by spin-orbit torque (SOT) is being intensely pursued. Especially, how to control the switching current density, which is expected to enrich device functionalities, has aroused much interest among researchers all over the world. In this paper, a novel method to adjust the switching current is proposed, and the BiFeO3 (BFO) based heterostructures with opposite spontaneous polarizations fields show huge changes in both perpendicular magnetic anisotropy and the SOT-induced magnetization switching. The damping-like torques were estimated by using harmonic Hall voltage measurement, and the variation of effective spin Hall angles for the heterostructures with opposite polarizations was calculated to be 272%. At the end of this paper, we have also demonstrated the possible applications of our structure in memory and reconfigurable logic devices.

The spin Hall magnetoresistance (SMR) and anomalous Hall effect (AHE) are observed in a Cr2O3/Ta structure. The structural and surface morphology of Cr2O3/Ta bilayers have been investigated. Temperature dependence of longitudinal and transverse resistances measurements confirm the relationship between SMR and AHE signals in Cr2O3/Ta structure. By means of temperature dependent magnetoresistance measurements, the physical origin of SMR in the Cr2O3/Ta structure is revealed, and the contribution to the SMR from the spin current generated by AHE has been proved. The so-called boundary magnetization due to the bulk antiferromagnetic order in Cr2O3 film may be responsible for the relationship of SMR and AHE in the Cr2O3/Ta bilayer.

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))

We report the enhancement of spin-orbit torques 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. Both damplinglike effective field HD and fieldlike effective field HF have been increased in the temperature range of 50 to 300 K. HD varies inversely with MS in both of the films, while the HF becomes liner dependent on 1/MS in the annealed film. We infer that the improved chemical ordering has enhanced the interfacial spin transparency and the transmitting of the spin current in MnAl layer.

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

We report room temperature ferromagnetism in boron-doped ZnO both experimentally and theoretically. The single phase Zn1-xBxO films deposited under high oxygen pressure by pulsed-laser deposition show ferromagnetic behavior at room temperature. The saturation magnetization increases monotonously from 0 to 1.5 emu/cm3 with the increasing of B component x from 0 to 6.8%. The first-principles calculations based on density functional theory demonstrate that the ferromagnetism in B-doped ZnO originates from the induced magnetic moments of oxygen atoms in the nearest neighbor sites to the B-Zn vacancy pair. The calculated total magnetic moment increasing tendency with B component is well consistent with experiments., Comment: 16 pages, 1 table, 4 figures.

Heusler alloy Co2FeAl was employed as ferromagnetic layers in Co2FeAl/Ru/Co2FeAl synthetic antiferromagnet structures. The experimental results show that the structure with a Ru thickness of 0.45 nm takes on strongly antiferromagnetic coupling, which maintains up to 150 oC annealing for 1 hour. The structure has a very low saturation magnetization Ms of 425 emu/cc, a low switching field Hsw of 4.3 Oe and a high saturation field Hs of 5257 Oe at room temperature, which are favorable for application in ultrahigh density magnetic read heads or other magnetic memory devices. XRD study testifies that the as-deposited Co2FeAl film is in B2 phase. Therefore Heusler alloys can be used to fabricate SyAF and it is possible to make "all-Heusler" spin-valves or magnetic tunneling junctions with better magnetic switching properties and high magnetoresistance., Comment: 12 pages, 6 figures

Ultrafast lasers have become one of the most powerful tools in coherent nonlinear optical spectroscopy. Short pulses enable direct observation of fast molecular dynamics, whereas broad spectral bandwidth offers ways of controlling nonlinear optical processes by means of quantum interferences. Special care is usually taken to preserve the coherence of laser pulses as it determines the accuracy of a spectroscopic measurement. Here we present a new approach to coherent Raman spectroscopy based on deliberately introduced noise, which increases the spectral resolution, robustness and efficiency. We probe laser induced molecular vibrations using a broadband laser pulse with intentionally randomized amplitude and phase. The vibrational resonances result in and are identified through the appearance of intensity correlations in the noisy spectrum of coherently scattered photons. Spectral resolution is neither limited by the pulse bandwidth, nor sensitive to the quality of the temporal and spectral profile of the pulses. This is particularly attractive for the applications in microscopy, biological imaging and remote sensing, where dispersion and scattering properties of the medium often undermine the applicability of ultrafast lasers. The proposed method combines the efficiency and resolution of a coherent process with the robustness of incoherent light. As we demonstrate here, it can be implemented by simply destroying the coherence of a laser pulse, and without any elaborate temporal scanning or spectral shaping commonly required by the frequency-resolved spectroscopic methods with ultrashort pulses., Comment: To appear in Nature Physics