Observation of the Fluctuation Spin Hall Effect in a Low-Resistivity Antiferromagnet.

The spin Hall effect (SHE) can generate a pure spin current by an electric current, which is promisingly used to electrically control magnetization. To reduce the power consumption of this control, a giant spin Hall angle (SHA) in the SHE is desired in low-resistivity systems for practical applications. Here, critical spin fluctuation near the antiferromagnetic (AFM) phase transition in chromium (Cr) is proven to be an effective mechanism for creating an additional part of the SHE, named the fluctuation spin Hall effect. The SHA is significantly enhanced when the temperature approaches the Néel temperature (TN) of Cr and has a peak value of -0.36 near TN. This value is higher than the room-temperature value by 153% and leads to a low normalized power consumption among known spin-orbit torque materials. This study demonstrates the critical spin fluctuation as a prospective way to increase the SHA and enriches the AFM material candidates for spin-orbitronic devices.

Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control.

The demonstration of the charge-to-spin conversion, especially with enhanced spin Hall conductivity, is crucial for the development of energy-efficient spintronic devices such as spin-orbit torque (SOT) based magnetoresistive random access memories. In this work, fully epitaxial Ru/Cu heterostructures were fabricated with interface engineering and nanolayer insertions consisting of Cu (1 nm)/Ru (1 nm) structures with different numbers of periods. The atomically controlled interface was confirmed by the high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the epitaxial relationship persists even in the hybrid nanolayer insertion structures. The spin current generation was detected by the measurement of unidirectional spin Hall magnetoresistance, and the effective damping-like spin Hall efficiency (ξDL) was further quantitatively evaluated by the spin-torque ferromagnetic resonance with thickness dependence of the ferromagnetic layer. It is found that the sharp interface Ru/Cu film has a sizeableξDLof -2.2% and the insertion of Cu/Ru nanolayers at the interface can increase theξDLvalue to -3.7%. The former could be attributed to the interface spin-orbit filtering effect and the latter may be further understood by the intrinsic contribution from the local electronic structure tuning due to the lattice distortion near the interface. A large effective spin Hall conductivity is achieved to be (3∼5) × 105ℏ2eΩ-1m-1in the epitaxial Ru/Cu hybrid nanolayers, which is in the same range as that of platinum. This work indicates that the interfacial control with hybrid nanolayer structures can extend the SOT-based materials to highly conductive metals, even with weak spin-orbit interactions, toward high stability, low cost, and low energy consumption for spintronic applications.

Spin Seebeck effect mediated reversal of vortex-Nernst effect in superconductor-ferromagnet bilayers.

We report on the observation of sign reversal of vortex-Nernst effect in epitaxial NbN/Fe bilayers deposited on MgO (001) substrates. Strong coupling between vortex magnetisation and ferromagnetic magnetisation at the NbN/Fe bilayer interface is presented. In NbN/Fe bilayer thin films an apparent sign reversal of vortex-Nernst signal under a temperature gradient with magnetic field and temperature is observed when the thickness of Fe is increased up to 5 nm. This reversal of the vortex-Nernst effect is associated with the enhancement of the spin Seebeck effects (SSE) near Tc due to coherence peak effect (CPE) and strong coupling of vortex magnetisation and ferromagnetic magnetisation at the interface of the NbN/Fe bilayer. The observed large SSE via inverse spin Hall effect (ISHE) is due to the CPE below and close to TC, highlighting the high spin to charge conversion efficiency of NbN in this region. This work may contribute to the development of superconducting spintronic devices by engineering the coupling of the superconductor/ferromagnet interface.

Ceramide synthase 3 affects invasion and metastasis of hepatocellular carcinoma via the SMAD6 gene. / ç¥žç»é °èƒºåˆæˆé ¶3通过SMAD6åŸºå› å½±å“è‚ç»†èƒžç™Œçš„ä¾µè¢­å’Œè½¬ç§».

OBJECTIVES: Patients with hepatocellular carcinoma (HCC) have poor prognosis due to lack of early diagnosis and effective treatment. Therefore, there is an urgent need to better understand the molecular mechanisms associated with HCC and to identify effective targets for early diagnosis and treatment. This study is to explore the expression and biological role of ceramide synthase 3 (CerS3) in HCC. METHODS: A total of 159 pairs of HCC tissues and adjacent non-tumor tissues were obtained from the patients underwent radical resection in Shenzhen People's Hospital, and the total RNA and proteins from HCC tissues and adjacent non-tumor tissues were obtained. The expression of CerS3 protein and mRNA in HCC was detected by immunohistochemistry, Western blotting and real-time PCR. In vitro experiments, Hep3B cells were divided into a control vector group and a CerS3 vector group, and the cells were transfected with retroviral vector containing control cDNA or CerS3 cDNA, respectively. HCCLM3 cells were divided into a normal control shRNA group and a CerS3 shRNA group, and the cells were transfected with lentiviral vectors containing normal control shRNA or CerS3 shRNA, respectively. MTT, EdU, Transwell and scratch method were used to detect cell proliferation, migration and invasion. RNA sequencing was performed to determine the downstream signal of CerS3. RESULTS: Compared with the corresponding adjacent tissues,the mRNA and protein levels of CerS3 were elevated in the HCC tissues, with significant difference (both P<0.05). The Univariate and multivariate analysis showed that the overall survival rate was significantly correlated with the presence of venous invasion (95% CI 1.8-9.2, P<0.01), TNM stage (95% CI 2.3-5.2, P<0.05), poor histological grade (95% CI 1.4-6.8, P<0.05), and CerS3 (95% CI 1.5-3.9, P<0.05). Furthermore, the high CerS3 expression levels in tumor tissues were significantly associated with shorter overall survival rates compared with the low CerS3 expression (P<0.05). Compared with the vector control group, the Hep3B cell viability, EdU positive cells, and migration and invasion cell numbers in the CerS3 vector group were significantly increased (all P<0.05). Compared with the shRNA normal control group, the HCCLM3 cell viability, EdU positive cells, and numbers of migrating and invasive cells in the CerS3 shRNA group were significantly lower (all P<0.05). The RNA sequencing confirmed that the small mothers against decapentaplegic family member 6 (SMAD6) gene as an oncogenic gene could promote the HCC metastasis. CONCLUSIONS: Clinically, the overexpression of CerS3 is closely related to poor clinical features and poor prognosis. Functionally, CerS3 participates in the proliferation, invasion and metastasis of liver cancer cells via activating SMAD6 gene.

Colossal Anomalous Hall Effect in Ferromagnetic van der Waals CrTe2.

van der Waals crystals exhibit excellent material performance when exfoliated to few-atomic-layer thickness. In contrast, the van der Waals thin films more than 10 nm thick are believed to show bulk properties, in which outstanding material performance is rarely found. Here we report the largest anomalous Hall conductivity observed so far in a 170 nm van der Waals ferromagnetic 1T-CrTe2 flake, which reaches 67,000 Ω-1 cm-1. Such a colossal anomalous Hall conductivity in 1T-CrTe2 is dominated by the extrinsic skew scattering process rather than the intrinsic Berry phase effect, as evidenced by the linear relation between the anomalous Hall conductivity and the longitudinal conductivity. Defying the dilemma of mutually exclusive large anomalous Hall angle and high electric conductivity for most ferromagnets, 1T-CrTe2 achieves both in a thin film sample. Considering the shared physics of the anomalous Hall effect and the spin Hall effect, our finding offers a guideline for searching large spin Hall materials of high conductivity which may overcome the bottleneck of overheating in spintronics devices.

Spin-charge conversion in NiMnSb Heusler alloy films.

Half-metallic Heusler alloys are attracting considerable attention because of their unique half-metallic band structures, which exhibit high spin polarization and yield huge magnetoresistance ratios. Besides serving as ferromagnetic electrodes, Heusler alloys also have the potential to host spin-charge conversion. Here, we report on the spin-charge conversion effect in the prototypical Heusler alloy NiMnSb. An unusual charge signal was observed with a sign change at low temperature, which can be manipulated by film thickness and ordering structure. It is found that the spin-charge conversion has two contributions. First, the interfacial contribution causes a negative voltage signal, which is almost constant versus temperature. The second contribution is temperature dependent because it is dominated by minority states due to thermally excited magnons in the bulk part of the film. This work provides a pathway for the manipulation of spin-charge conversion in ferromagnetic metals by interface-bulk engineering for spintronic devices.

Interface Tailoring Effect for Heusler Based CPP-GMR with an L12-Type Ag3Mg Spacer.

Current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effects are of interest in a possible application of magnetic sensor elements, such as read-head of hard disk drives. To improve the junction performance, the interface tailoring effects were investigated for the Heulser alloy, Co2Fe0.4Mn0.6Si (CFMS), based CPP-GMR junctions with an L 1 2 -Ag3Mg ordered alloy spacer. Ultra-thin Fe or Mg inserts were utilized for the CFMS/Ag3Mg interfaces, and CPP-GMR at low bias current density, J and the J dependence were evaluated for the junctions. Although, at low bias J, MR ratio decreased with increasing the inserts thickness, the device output at high bias J exhibited quite weak dependence on the insert thickness. The output voltages of the order of 4 mV were obtained for the junctions regardless of the insert at an optimal bias J for each. The critical current density J c was evaluated by the shape of MR curves depending on J. J c increased with the insert thicknesses up to 0.45 nm. The enhancement of J c suggests that spin-transfer-torque effect may reduce in the junctions with inserts, which enables a reduction of noise and can be an advantage for device applications.

Voltage control of magnetic anisotropy in epitaxial Ru/Co2FeAl/MgO heterostructures.

Voltage control of magnetic anisotropy (VCMA) in magnetic heterostructures is a key technology for achieving energy-efficiency electronic devices with ultralow power consumption. Here, we report the first demonstration of the VCMA effect in novel epitaxial Ru/Co2FeAl(CFA)/MgO heterostructures with interfacial perpendicular magnetic anisotropy (PMA). Perpendicularly magnetized tunnel junctions with the structure of Ru/CFA/MgO were fabricated and exhibited an effective voltage control on switching fields for the CFA free layer. Large VCMA coefficients of 108 and 139 fJ/Vm for the CFA film were achieved at room temperature and 4 K, respectively. The interfacial stability in the heterostructure was confirmed by repeating measurements. Temperature dependences of both the interfacial PMA and the VCMA effect were also investigated. It is found that the temperature dependences follow power laws of the saturation magnetization with an exponent of ~2, where the latter is definitely weaker than that of conventional Ta/CoFeB/MgO. The significant VCMA effect observed in this work indicates that the Ru/CFA/MgO heterostructure could be one of the promising candidates for spintronic devices with voltage control.

Fully epitaxial C1b-type NiMnSb half-Heusler alloy films for current-perpendicular-to-plane giant magnetoresistance devices with a Ag spacer.

Remarkable magnetic and spin-dependent transport properties arise from well-designed spintronic materials and heterostructures. Half-metallic Heusler alloys with high spin polarization exhibit properties that are particularly advantageous for the development of high-performance spintronic devices. Here, we report fully (001)-epitaxial growth of a high-quality half-metallic NiMnSb half-Heusler alloy films, and their application to current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with Ag spacer layers. Fully (001)-oriented NiMnSb epitaxial films with very flat surface and high magnetization were prepared on Cr/Ag-buffered MgO(001) single crystalline substrates by changing the substrate temperature. Epitaxial CPP-GMR devices using the NiMnSb films and a Ag spacer were fabricated, and room-temperature (RT) CPP-GMR ratios for the C1b-type half-Heusler alloy were determined for the first time. A CPP-GMR ratio of 8% (21%) at RT (4.2 K) was achieved in the fully epitaxial NiMnSb/Ag/NiMnSb structures. Furthermore, negative anisotropic magnetoresistance (AMR) ratio and small discrepancy of the AMR amplitudes between RT and 10 K were observed in a single epitaxial NiMnSb film, indicating robust bulk half metallicity against thermal fluctuation in the half-Heusler compound. The modest CPP-GMR ratios could be attributed to interface effects between NiMnSb and Ag. This work provides a pathway for engineering a new class of ordered alloy materials with particular emphasis on spintronics.

Manipulation of magnetization switching and tunnel magnetoresistance via temperature and voltage control.

Magnetization switching between parallel and antiparallel alignments of two magnetic layers in magnetic tunnel junctions (MTJs) is conventionally controlled either by an external magnetic field or by an electric current. Here, we report that the manipulation of magnetization switching and tunnel magnetoresistance (TMR) in perpendicularly magnetized CoFeB/MgO/CoFeB MTJs can be achieved by both temperature and voltage. At a certain range of temperature, coercivity crossover between top and bottom magnetic layers is observed in which the TMR ratio of the MTJs is almost unmeasurable. Furthermore, the temperature range can be tuned reversibly by an electric voltage. Magnetization switching driven by the voltage reveals an unconventional phenomenon such that the voltage driven coercivity changes with temperature are quite different for top and bottom CoFeB layers. A model based on thermally-assisted domain nucleation and propagation is developed to explain the frequency and temperature dependence of coercivity. The present results of controlling the magnetization switching by temperature and voltage may provide an alternative route for novel applications of MTJs based spintronic devices.

A 4-fold-symmetry hexagonal ruthenium for magnetic heterostructures exhibiting enhanced perpendicular magnetic anisotropy and tunnel magnetoresistance.

A 4-fold-symmetry hexagonal Ru emerging in epitaxial MgO/Ru/Co2 FeAl/MgO heterostructures is reported, in which an approximately Ru(022¯3) growth attributes to the lattice matching between MgO, Ru, and Co2 FeAl. Perpendicular magnetic anisotropy of the Co2 FeAl/MgO interface is substantially enhanced. The magnetic tunnel junctions (MTJs) incorporating this structure give rise to the largest tunnel magnetoresistance for perpendicular MTJs using low damping Heusler alloys.