Jinglan Chen

Magnetostructural Transformation and Magnetoresponsive Properties of

The martensitic and magnetic phase transformations in MnNiGe_1-xSn_x (0 ≤ <i>x</i> ≤ 0.200) alloys were investigated using X-ray diffraction, differential thermal analysis, and magnetization measurements. Results indicate that increasing the Sn substitution in MnNiGe_1-xSn_x results in 1) a decrease of the martensitic transformation temperature from 460 to 100 K and 2) a conversion of spiral antiferromagnetic (AFM) to antiparallel AFM structure in martensite. Based on these features, a remarkable magnetic-field-induced paramagnetic/spiral AFM and FM/AFM magnetostructural transformations are found, and large positive and negative magnetocaloric effects are obtained. The magnetoresponsive effects of MnNiGe_1-xSn_x alloys are enhanced by Sn substitution. A structural and magnetic phase diagram of MnNiGe_1-xSn_x alloys has been proposed.

{\rm MnNiGe}_{1-x}{\rm Sn}_{x}

The first-principles calculation within density-functional theory is used to search for new candidates of half-metallic ferromagnets in semi-Heusler alloys NiCrM (M = P, As, Sb, S, Se and Te). Our calculations predict that NiCrP, NiCrSe and NiCrTe are half-metallic ferromagnets (HMFs) with magnetic moments of nearly 3 or 4 μB/fu and HM gaps of 0.263, 0.047 and 0.102 eV, respectively. Other compounds are so-called nearly HMFs. Substitution of the sp atoms cannot be responsible for the formation of the band gap, but results in a shift in the Fermi level and the loss of half-metallicity. The half-metallicity of NiCrP and NiCrTe can be retained when the lattice parameter is changed by about 2%–3%.

Alloys

The numerical simulation of the open recoil loops has been carried out using micromagnetic finite element method. By giving an example for this issue, the magnetization behaviors during the recoil processes of nanocomposite Pr2Fe14B∕α-Fe magnets have been analyzed. It is the strong intergrain exchange coupling that results in the magnetization reversal in some hard grains during the recoil processes, which leads to the large opening of recoil loops. The magnetization reversal of α-Fe grain follows that of its neighboring hard grains. Consequently, the opening of recoil loops is enhanced due to the presence of α-Fe grains.

Search for new half-metallic ferromagnets in semi- Heusler alloys NiCrM (M = P, As, Sb, S, Se and Te)

The Co2NiGa alloy with a fcc structure was synthesized by different methods, arc-melting and mechanical alloying. In contrast with the solid solution state in melted Co2NiGa, an intermetallic structure, highly ordered atomic arrangement has been verified in ball-milled sample by x-ray diffraction examination and Rietveld analysis. This ordered structure increases the saturation magnetization about 40% higher than that of solid solution sample. A highly ordered Co2NiGa intermetallic compound model was established for carrying out first-principles calculation. The obtained electronic structure and the molecular moment are quite consistent with the experimental results. The characterization of the samples prepared in different alloying processes is also reported.

The physical origin of open recoil loops in nanocrystalline permanent magnets

We report on structural, magnetic, transport, and spin polarization measurements of a new semi-Heusler alloy NiFeSb, which was synthesized successfully by means of electron melt-spinning technique although its ferromagnetic state and crystal structure was predicted to be unstable by the band calculation. The temperature-dependent measurement of magnetizations can both be interpreted well by the spin-wave theory. The electrical resistivity follows a T-5 behavior at low temperatures. Point contact Andreev reflection measurements of the spin polarization yield moderate polarization of 52%

Structure and magnetic properties of highly ordered Co2NiGa alloys

209Bi nuclear magnetic resonance (NMR) spectroscopy was employed to probe potential spin-orbit effects on orbital diamagnetism in YPtBi and YPdBi crystals. The observed opposite sign and temperature dependent magnitude of 209Bi NMR shifts of both crystals reveal experimental signatures of enhanced orbital diamagnetism induced by spin-orbit interactions. This investigation indicates that NMR isotropic shifts might be beneficial in search of interesting spin-electronic phases among a vast number of topological nontrivial half-Heusler semimetals.

A new semi-Heusler ferromagnet NiFeSb: electronic structure, magnetism and transport properties

Sngle crystals of Tb0.3Dy0.7Fe2 have been obtained by CZ technique with cold crucible. The formation mechanism of defects such as RFe3 strips, Widmanstatten precipitates (WSP), twins and inclusions were investigated in detail. They are generated by different phase relations and conditions of solidification. The geometrical morphology depends on the crystallographic orientation or the position of the interface. The relationship between growth conditions and compositions of starting materials has been discussed based on the normal freezing theory for rare earth-rich growth environment. Various growth rates were selected for growing defect-free single crystals of Tb0.3Dy0.7Fe2. Optimized conditions are a growth rate of 10-30mm/h, temperature gradient of 110-140degreesC/cm and starting composition of Tb0.3Dy0.7Fey (y = 1.78-1.85)

NMR investigation of atomic and electronic structures of half-Heusler topologically nontrivial semimetals

CORRIGENDUM: Large Linear Magnetoresistance and Shubnikov-de Hass Oscillations in Single Crystals of YPdBi Heusler Topological Insulators