Wang Dun-Hui

Martensitic transformation and related magnetic effects in Ni—Mn-based ferromagnetic shape memory alloys

Ferromagnetic shape memory alloys, which undergo the martensitic transformation, are famous multifunctional materials. They exhibit many interesting magnetic properties around the martensitic transformation temperature due to the strong coupling between magnetism and structure. Tuning magnetic phase transition and optimizing the magnetic effects in these alloys are of great importance. In this paper, the regulation of martensitic transformation and the investigation of some related magnetic effects in Ni—Mn-based alloys are reviewed based on our recent research results.

The magnetic phase transition and the low-field Arrott plots of (GDxDy1−x)Co2 compounds

Abstract A series of (GdxDy1−x)Co2 (0–0.55) compounds have been prepared by arc-melting method. In order to determine the phase transition order in these compounds, we have performed some magnetization measurements. Only from the plots of temperature dependence of magnetization and the low-field magnetization isotherms, it is difficult to judge the phase transition order. The low-field Arrott plot is proved to be a more reliable method to characterize the first-order transition and the second-order transition. No first-order transition is observed in (GdxDy1−x)Co2 compounds (x≠0). The result is discussed in the Inoue-Shimizu like model.

The origin of the large magnetocaloric effect in RCo2 (R=Er, Ho and Dy)

The phase transitions of the RCo2 (R=Er, Ho and Dy) compounds are of first-order type and a metamagnetic transition is observed above the Curie temperature. Owing to their large magnetic entropy change, the RCo2 compounds are competitive candidates as the working substance for magnetic refrigeration. In this paper we discuss the origin of this large magnetic entropy change.

Multiferroic properties in terbium orthoferrite

Multiferroic properties in a polycrystalline terbium orthoferrite are investigated. Different thermomagnetic behaviors are observed in different magnetic fields, which is attributed to the suppression of the low temperature magnetic phase by an external magnetic field. Further studies reveal that the ferroelectricity originates from the spin configuration below 3.5 K. In addition, the magnetic field control of electric polarization and dielectric constant is observed, which suggests a magnetoelectric effect in TbFeO3. The origin of ferroelectricity in this rare-earth orthoferrite is discussed.

Magnetic phase transitions and magnetocaloric effect in the Fe-doped MnNiGe alloys

The magnetic phase transition and magnetocaloric effects in Fe-doped MnNiGe alloys are investigated. The substitution of Fe for Ni decreases the structural transition temperature remarkably, resulting in the magnetostructural transition occurring between antiferromagnetic and ferromagnetic states in MnNi1−xFexGe alloy. Owing to the enhanced ferromagnetic coupling induced by the substitution of Fe, metamagnetic behaviour is also observed in TiNiSi-type phase of MnNi1−xFexGe alloys at temperature below the structural transition temperature.

Magnetic phase transition and magnetocaloric effect in Mn1?xZnxCoGe alloys

The magnetic phase transition and magnetocaloric effect are studied in a series of Mn1−xZnxCoGe (x = 0.01, 0.02, 0.04, and 0.08) alloys. By introducing a small quantity of Zn element, the structural transformation temperature of the MnCoGe alloy is greatly reduced and a first-order magnetostructural transition is observed. Further increasing the Zn concentration results in a second-order ferromagnetic transition. Large room-temperature magnetocaloric effects with small magnetic hysteresis are obtained in alloys with x = 0.01 and 0.02, which suggests their potential application in magnetic refrigeration.

Multiferroicity in B-site ordered double perovskite Y2MnCrO6

Double perovskite manganite Y2MnCrO6 ceramic is synthesized and its multiferroic properties are investigated. Novel multiferroic properties are displayed with respect to other multiferroics, such as high ferroelectric phase transition temperature, and the coexistence of ferrimagnetism and ferroelectricity. Moreover, the ferroelectric polarization of Y2MnCrO6 below the magnetic phase temperature can be effectively tuned by an external magnetic field, showing a remarkable magnetoelectric effect. These results open an effective avenue to explore magnetic multiferroics with spontaneous magnetization and ferroelectricity, as well as a high ferroelectric transition temperature.

Magnetic Properties and Intergranular Action in Bonded Hybrid Magnets

Abstract Magnetic properties and intergranular action in bonded hybrid magnets, based on NdFeB and strontium ferrite powders were investigated. The long-range magnetostatic interaction and short-range exchange coupling interaction existed simultaneously in bonded hybrid magnets, and neither of them could be neglected. Some magnetic property parameters of hybrid magnets could be approximately obtained by adding the hysteresis loops of two magnets pro rata.

Multiple sign reversals of the exchange bias field in polycrystalline SmCr0.9Fe0.1O3

We synthesize the perovskite compound SmCr0.9Fe0.1O3 by the sol–gel method and investigate its exchange bias properties through thermomagnetic and isothermal magnetization measurements. The sign reversals of the exchange bias field are observed at the magnetization compensation temperatures 29.6 K and 96.2 K. It is demonstrated that the occurrence of the exchange bias originates from the antiferromagnetic coupling between the Cr-rich and Fe–Cr regions, of which the net magnetization is temperature-dependent. These results imply that there are potential applications in single systems with sign reversals of both magnetization and exchange bias.

Modulation of magnetic properties and enhanced magnetoelectric effects in MnW1?xMoxO4 compounds

In this letter, we investigate the magnetic and ferroelectric properties of polycrystalline MnW1–xMoxO4 (x = 0, 0.05, 0.10, 0.20) compounds. The substitution of nonmagnetic Mo6+ ions for W6+ ions modifies the magnetic transition temperatures of MnW1–xMoxO4 by changing the Mn—O—Mn bond. As a result, distinct ferroelectric properties and enhanced magnetoelectric effects are observed in Mo6+ -doped MnWO4 compounds. The effects of substitution of Mo6+ ions on magnetic properties and magnetoelectric coupling are discussed.