Dunhui Wang

The magnetostructural transformation and magnetocaloric effect in Co-doped MnNiGe1.05 alloys

A series of MnNi1−xCoxGe1.05 (x = 0, 0.03, 0.05, 0.07, 0.09, and 0.11) alloys were prepared by the arc-melting method. With increasing content of Co, a first-order magnetostructural transformation between the antiferromagnetic TiNiSi-type phase and the ferromagnetic Ni2In-type phase was observed. A magnetic and crystallographic phase diagram for MnNi1−xCoxGe1.05 alloys was proposed in this paper. Owing to the abrupt and large jump of magnetization around the magnetostructural transformation, MnNi1−xCoxGe1.05 (x = 0.07, 0.09, 0.11) alloys show large and positive magnetic entropy changes at relatively low field.

Electric field control of the magnetocaloric effect.

Through strain-mediated magnetoelectric coupling, it is demonstrated that the magnetocaloric effect of a ferromagnetic shape-memory alloy can be controlled by an electric field. Large hysteresis and the limited operating temperature region are effectively overcome by applying an electric field on a laminate comprising a piezoelectric and the alloy. Accordingly, a model for an active magnetic refrigerator with high efficiency is proposed in principle.

Structural and electrical properties of homologous Srm−3Bi4TimO3m+3 (m=3, 4, 5, and 6) thin films

Polycrystalline thin films of Bi-layered Srm−3Bi4TimO3m+3 (referred to as BTO for m=3 and SBTim for m=4,5, and 6 respectively) were fabricated on Pt-coated silicon substrates by pulsed laser deposition. Structures were characterized by x-ray diffraction, atomic force microscopy, and scanning electron microscopy. Electric properties were investigated systematically. It was revealed that the remnant polarization Pr depended greatly on the parity of m. This dependence was well explained by using a rotating oxygen octahedra model along the a axis. The superior fatigue properties of SBTim (m=4,5,6) over BTO films were discussed in detail. The high dielectric constants and low dissipation factors of the films were demonstrated.

Manipulation of anisotropic magnetoresistance and domain configuration in Co/PMN-PT (011) multiferroic heterostructures by electric field

The electric field manipulation of magnetic anisotropy and domain configuration has been investigated in the artificial multiferroic Co/PMN-PT (011) heterostructure at room temperature. A uniaxial magnetic anisotropy is induced with the application of an electric field, which leads to an electrically switched anisotropic magnetoresistance with tunability as large as ∼29%. Furthermore, the magnetic domain structures of Co films are investigated by magnetic force microscopy under an in situ electric field, which exhibits direct evidence for electric field control of magnetism at the mesoscale. The converse magnetoelectric effect demonstrated in this multiferroic heterostructure has potential to be utilized in magnetoelectric devices with low power consumption.

Effect of metamagnetism on multiferroic property in double perovskite Sm2CoMnO6

The magnetic and multiferroic properties of a B-site ordered double perovskite Sm2CoMnO6 are investigated. The electric polarization is observed below the ferromagnetic Curie temperature of 135u2009K. This electric polarization of Sm2CoMnO6 can be influenced by applying a magnetic field, showing an interesting magnetoelectric effect. The origins of multiferroic properties and magnetoelectric effect are discussed.

Enhanced Photocatalytic Performance through Magnetic Field Boosting Carrier Transport

The promotion of magnetic field on catalytic performance has attracted extensive attention for a long time, and substantial improvements have been achieved in some catalysis fields. However, because the Zeeman energy is several orders of magnitude weaker, magnetic field seems unable to alter the band structure and has a negligible effect on semiconductor photocatalytic performance, which makes this task a great challenge. On the other hand, the spin-related behavior usually plays an important role in determining catalytic performance. For example, in some molecular catalysis, such as photosystem II, ferromagnetic alignment of the active material results in spin-oriented electrons, which are selected and accumulated at the interface, leading to great promotion of the oxygen evolution reaction activity. Here, we propose a magnetoresistance-related strategy to boost the carrier transfer efficiency and apply it in α-Fe2O3/reduced graphene oxide hybrid nanostructures (α-Fe2O3/rGO) to improve the photocatalytic performance under magnetic field. We show that both the degradation rate constant and photocurrent density of α-Fe2O3/rGO can be dramatically enhanced with the application of magnetic field, indicating the promotion of the photocatalytic performance.

Combined caloric effects in a multiferroic Ni–Mn–Ga alloy with broad refrigeration temperature region

Solid-state refrigeration based on the caloric effects is promising to replace the traditional vapor-compressing refrigeration technology due to environmental protection and high efficiency. However, the narrow working temperature region has hindered the application of these refrigeration technologies. In this paper, we propose a method of combined caloric, through which a broad refrigeration region can be realized in a multiferroic alloy, Ni–Mn–Ga, by combining its elastocaloric and magnetocaloric effects. Moreover, the materials’ efficiency of elastocaloric effect has been greatly improved in our sample. These results illuminate a promising way to use multiferroic alloys for refrigeration with a broad refrigeration temperature region.

Electric control of magnetism and magnetocaloric effects in LaFe11.4Si1.6H1.5 using ferroelectric PMN-PT

The alloy with first-order magnetic phase transition has an advantage to exhibit large magnetoelectric effect in strain-mediated multiferroic composites, since the strain can drive its phase transition and consequently lead to a large magnetic change. In the present paper, we investigate the electric field manipulation of magnetic and magnetocaloric properties in LaFe11.4Si1.6H1.5/Pb(Mg1/3Nb2/3)O3–PbTiO3 laminate. By applying an electric field on the ferroelectric substrate, the relative change of magnetization has a peak value of −8% around the Curie temperature, showing a large converse magnetoelectric effect. As for the magnetocaloric performance, the peak temperature of magnetic entropy change (ΔS M) has a shift of 3 K to low temperature and the maximal value of ΔS M keeps almost unchanged under an electric field of 8 kV cm−1. Moreover, the thermal and magnetic hysteresis can be reduced as well with the application of the electric field.

Tuning of the microwave magnetization dynamics in CoZr-based thin films by Nd-doping

To enhance the damping of microwave magnetization dynamics, we investigate the effect of Nd-doping (0–3.0 at. %) into CoZr thin films. The saturation magnetization decreases with Nd-doping. The coercivities generally decrease in the case of 1.5 at. % Nd-doping, while increase in the case of 3.0 at. % Nd-doping. The magnetization dynamics is characterized with the permeability spectra, which are determined by the ferromagnetic resonance behavior at the microwave range. The permeability spectra are analyzed through the fittings with Landau-Lifshitz-Gilbert equation. From the fittings, both the dynamic magnetic anisotropy field and the damping factor increase, due to the enhanced spin-orbital coupling by Nd-doping.