Deterministic reversal of single magnetic vortex circulation by an electric field.

The ability to control magnetic vortex is critical for their potential applications in spintronic devices. Traditional methods including magnetic field, spin-polarized current etc. have been used to flip the core and/or reverse circulation of vortex. However, it is challenging for deterministic electric-field control of the single magnetic vortex textures with time-reversal broken symmetry and no planar magnetic anisotropy. Here it is reported that a deterministic reversal of single magnetic vortex circulation can be driven back and forth by a space-varying strain in multiferroic heterostructures, which is controlled by using a bi-axial pulsed electric field. Phase-field simulation reveals the mechanism of the emerging magnetoelastic energy with the space variation and visualizes the reversal pathway of the vortex. This deterministic electric-field control of the single magnetic vortex textures demonstrates a new approach to integrate the low-dimensional spin texture into the magnetoelectric thin film devices with low energy consumption.

Evidence of Pure Spin-Current Generated by Spin Pumping in Interface-Localized States in Hybrid Metal-Silicon-Metal Vertical Structures.

Due to the difficulty of growing high-quality semiconductors on ferromagnetic metals, the study of spin diffusion transport in Si was limited to lateral geometry devices. In this work, by using an ultrahigh-vacuum wafer-bonding technique, we have successfully fabricated metal-semiconductor-metal CoFeB/MgO/Si/Pt vertical structures. We hereby demonstrate pure spin-current injection and transport in the perpendicular current flow geometry over a distance larger than 2 µm in n-type Si at room temperature. In those experiments, a pure propagating spin current is generated via ferromagnetic resonance spin pumping and converted into a measurable voltage by using the inverse spin Hall effect occurring in the top Pt layer. A systematic study varying both Si and MgO thicknesses reveals the important role played by the localized states at the MgO-Si interface for the spin-current generation. Proximity effects involving indirect exchange interactions between the ferromagnet and the MgO-Si interface states appears to be a prerequisite to establishing the necessary out-of-equilibrium spin population in Si under the spin-pumping action.

Anti-atherosclerotic effect of Fermentum Rubrum and Gynostemma pentaphyllum mixture in high-fat emulsion- and vitamin D3-induced atherosclerotic rats.

BACKGROUND: The mixture of Hongqu and gypenosides (HG) is composed of Fermentum Rubrum (Hongqu, in Chinese) and total saponins of Gynostemma pentaphyllum (Thunb.) Makino (Jiaogulan, in Chinese) in a 3.6:1 weight ratio. Both Hongqu and Jiaogulan are considered valuable traditional Chinese medicines (TCMs); they have been commonly used in China for the treatment of hyperlipidemia and related diseases for centuries. The aim of the current study was assess the anti-atherosclerotic effect of HG. METHODS: Sixty-four Wistar rats were randomly divided into eight groups: normal, model, positive control (simvastatin, 1 mg/kg), Hongqu-treated (72 mg/kg), gypenoside (total saponin)-treated (20 mg/kg), and three doses HG-treated (50, 100, and 200 mg/kg). All of the rats were fed a basal diet. Additionally, the model group rats were intragastrically administered a high-fat emulsion and intraperitoneally injected with vitamin D3. The serum lipid profiles, oxidative stress, inflammatory cytokine, and hepatic antioxidant levels were then determined. Furthermore, the liver histopathology and arterial tissue were analyzed, and the expression of hyperlipidemia- and atherosclerosis (AS)-related genes was measured using reverse transcription-polymerase chain reaction. RESULTS: The AS rat model was established after 80 days. Compared to the model group, the HG-treated groups showed an obvious improvement in the serum lipid profiles, oxidative stress, and inflammatory cytokine levels, and showed markedly increased hepatic total antioxidant capacity. Moreover, the expression of genes related to lipid synthesis and inflammation reduced and that of the genes related to lipid oxidation increased in the liver and arterial tissue, which also reflected an improved health condition. CONCLUSION: the anti-atherosclerotic effects of HG were superior to those of simvastatin, Hongqu, and the gypenosides. Therefore, HG may be a useful anti-atherosclerotic TCM preparation.

Ferroelastic switching in a layered-perovskite thin film.

A controllable ferroelastic switching in ferroelectric/multiferroic oxides is highly desirable due to the non-volatile strain and possible coupling between lattice and other order parameter in heterostructures. However, a substrate clamping usually inhibits their elastic deformation in thin films without micro/nano-patterned structure so that the integration of the non-volatile strain with thin film devices is challenging. Here, we report that reversible in-plane elastic switching with a non-volatile strain of approximately 0.4% can be achieved in layered-perovskite Bi2WO6 thin films, where the ferroelectric polarization rotates by 90° within four in-plane preferred orientations. Phase-field simulation indicates that the energy barrier of ferroelastic switching in orthorhombic Bi2WO6 film is ten times lower than the one in PbTiO3 films, revealing the origin of the switching with negligible substrate constraint. The reversible control of the in-plane strain in this layered-perovskite thin film demonstrates a new pathway to integrate mechanical deformation with nanoscale electronic and/or magnetoelectronic applications.

Giant barocaloric effect in hexagonal Ni2In-type Mn-Co-Ge-In compounds around room temperature.

The most widespread cooling techniques based on gas compression/expansion encounter environmental problems. Thus, tremendous effort has been dedicated to develop alternative cooling technique and search for solid state materials that show large caloric effects. An application of pressure to a material can cause a change in temperature, which is called the barocaloric effect. Here we report the giant barocaloric effect in a hexagonal Ni2In-type MnCoGe0.99In0.01 compound involving magnetostructural transformation, Tmstr, which is accompanied with a big difference in the internal energy due to a great negative lattice expansion(ΔV/V ~ 3.9%). High resolution neutron diffraction experiments reveal that the hydrostatic pressure can push the Tmstr to a lower temperature at a rate of 7.7 K/kbar, resulting in a giant barocaloric effect. The entropy change under a moderate pressure of 3 kbar reaches 52 J kg(-1) K(-1), which exceeds that of most materials, including the reported giant magnetocaloric effect driven by 5 T magnetic field that is available only by superconducting magnets.

Exchange-biased hybrid ferromagnetic-multiferroic core-shell nanostructures.

Artificial exchange-biased two-phase core-shell nanostructures consisting of ferromagnetic (Ni) and multiferroic (BiFeO3) materials were manufactured by a two-step method. An exchange bias effect was observed and studied, which indicates that it is possible to fabricate ferromagnetic-multiferroic nanostructures to utilize the combined ferroelectric and antiferromagnetic functionalities of bismuth ferrite.