Meng Fanbin

Magnetic properties and magnetocaloric effect in compound PrFe 12 B 6

Magnetic properties and magnetocaloric effect of compound PrFe12B6 are investigated. The coexistence of hard phase PrFe12B6 and soft phase α–Fe causes interesting phenomena on the curves for the temperature dependence of magnetization. PrFe12B6 experiences a first order phase transition at the Curie temperature 200 K, accompanied by an obvious lattice contraction, which in turn results in a large magnetic entropy change. The Maxwell relation fails to give the correct information about magnetic entropy change due to the first order phase transition nature. The large magnetic entropy changes of PrFe12.3B4.7 obtained from heat capacity method are 11.7 and 16.2 J/kg.K for magnetic field changes of 0–2 T and 0–5 T respectively.

Magnetocrystalline Anisotropy and Magnetoelasticity of Preferentially Oriented Martensitic Variants in Ni52Mn24Ga24 Single Crystals

The magnetocrystalline anisotropy and magnetoelasticity of preferentially oriented martensitic variants in an off-stoichiometric Ni52Mn24Ga24 single crystal have been investigated. We found that the easy magnetization direction of the martensite phase is the [110] direction, and the hard magnetization exhibited in [001], the growth direction of single crystals. The temperature dependence of the anisotropy fields and constants of Ni52Mn24Ga24 have been determined. It was found that, at the martensite phase, the anisotropy field increases monotonically with decreasing temperature, but the anisotropy constant first increases rapidly and then the increasing rate becomes smaller and smaller. Based on a previous model, the present results suggest that the competition between the Zeeman energy and the magnetocrystalline anisotropy energy is mainly responsible for the magnitude of magnetic-field-induced strain in this material.

Structure and magnetic properties of (Nd1?xErx)3Fe25Cr4.0 (0 ? x ? 0.8) compounds

The structure and magnetic properties of (Nd1-xErx)(3)Fe25Cr4.0 compounds with x = 0-0.8 have been investigated using x-ray powder diffraction (XRD) and magnetic measurements. It has been found that all the compounds crystallize in a Nd-3(Fe,Ti)(29)-type structure. Substitution of Er for Nd leads to a contraction of the unit-cell volume. The Curie temperature, T, and the saturation magnetization, M-s, of (Nd1-xErx)(3)Fe25Cr4.0 decrease monotonically with increasing Er content. The easy magnetization direction (EMD) of Nd3Fe25Cr4.0 at room temperature is close to the [040] direction but may be a little out of the basal plane. With increasing Er content, the EMD changes closer to the [40-2] direction and the tilt angle increases. Both the XRD patterns and ac susceptibility indicate the appearance of a spin reorientation for x = 0-0.4 as the temperature decreases from room temperature to 77 K. The spin reorientation temperature, T-sr, increases monotonically with increasing Er content from 158 K for x = 0 to 198 K for x = 0.4. A first order magnetization process (FOMP) occurs for all the compounds, and the critical field of the FOMP decreases with increasing Er content from 6.6 T for x = 0 to 2.0 T for x = 0.7.

Magnetoresistance and magnetic properties of Fe3O4 nanoparticle compacts

In this paper, we report on the magnetic properties of Fe3O4 nanoparticles with different grain sizes under different pressures. In all the samples, the saturated magnetization Ms shows a linear decrease with increasing pressure. The thickness of the magnetic dead layer on the nanoparticle surface under different pressures was roughly estimated, which also increases with increasing pressure. The transport measurements of the nanoparticle Fe3O4 compacts show that the low-field magnetoresistance (MR) value is insensitive to the grain size in a wide temperature range; however, the high-field MR value is dependent on grain size, especially at low temperatures. These experimental results can be attributed to the different surface states of the nanoparticles.

Successive phase transformation in ferromagnetic shape memory alloy Co37Ni34Al29 melt-spun ribbons ⁄

The martensitic transformation in Co37Ni34Al29 ribbon is characterized in detail by means of in-situ thermostatic x-ray difiraction and magnetic measurements. The results show a structural transition from the body-centred cubic to martensite with a tetragonal structure during cooling. Comparison between the results of the difiraction intensity with the magnetic susceptibility measurements indicates that the martensitic transformation takes place in several difierent steps during cooling from 273 to 163 K. During heating from 313 to 873 K, the peak width becomes very wide and the intensity turns very low. The ∞-phase (face-centred cubic structure) emerges and increases gradually with temperature increasing from 873 to 1073 K.