Y. X. Li

Vacancy-tuned paramagnetic/ferromagnetic martensitic transformation in Mn-poor Mn1-xCoGe alloys

It is shown that a temperature window between the Curie temperatures of martensite and austenite phases around the room temperature can be obtained by a vacancy-tuning strategy in Mn-poor Mn1-xCoGe alloys (0≤x≤0.050). Based on this, a martensitic transformation from paramagnetic austenite to ferromagnetic martensite with a large magnetization difference can be realized in this window. This gives rise to a magnetic-field–induced martensitic transformation and a giant magnetocaloric effect in the Mn1−xCoGe system. The decrease of the transformation temperature and of the thermal hysteresis of the transformation, as well as the stable Curie temperatures of martensite and austenite, are discussed on the basis of the Mn-poor Co-vacancy structure and the corresponding valence-electron concentration.

Reduction of hysteresis loss and large magnetic entropy change in the NaZn13-type LaPrFeSiC interstitial compounds

Magnetic properties and magnetic entropy change of the NaZn13-type La0.5Pr0.5Fe11.5Si1.5Cx compounds have been investigated. Both the lattice parameter and the Curie temperature increase linearly with increasing carbon concentration. The maximum hysteresis loss at TC reduces remarkably from 94.8J∕kg for x=0to23.1J∕kg for x=0.3 because of the weakening of the itinerant electron metamagnetic transition. However, the magnetic entropy change remains at the large values of 32.4J∕kgK for x=0 and 27.6J∕kgK for x=0.3 under a field change of 0–5T, which implies that a large magnetocaloric effect and a small hysteresis loss have been simultaneously achieved in the La0.5Pr0.5Fe11.5Si1.5Cx carbides.

Large magnetocaloric effect in spinel CdCr2S4

Magnetocaloric effect in CdCr2S4 was investigated by magnetization and heat capacity measurements. CdCr2S4 is of a cubic spinel structure with soft ferromagnetism and performs reversible magnetic entropy in the whole experimental temperature range from 56to128K. A large magnetic entropy change ∼7.04J∕kgK and adiabatic temperature change ΔTad∼2.6K are revealed for a field change of 0–5T near the Curie temperature of 87K. These results suggest that sulfospinel probably is a promising candidate as working material in magnetic refrigeration technology.

Superelasticity of CoNiGa : Fe single crystals

We have fabricated CoNiFeGa single crystals with excellent superelasticity. The superelastic strains of 4% and 6.7% in compression have been obtained along the [001] and [110] directions, respectively. These single crystals show strong anisotropy in strains, superelastic parameters, and even transformation path related to the different crystalline directions. A large superelastic strain up to 11% has been obtained in tension test. The perfect superelasticities have also displayed in bending and torsion tests.

Ferromagnetic exchange interaction between Co and Mn in the Heusler alloy CuCoMnAl

The ferromagnetic exchange interaction between Co and Mn in Heusler alloys has been phenomenologically investigated by analyzing the composition dependence of the magnetic moment and the Curie temperature in a series of quaternary CuCoMnAl alloys. The curves of the composition dependence of the magnetic moment show an interesting valleylike profile and their minima are positioned at different Co contents for different Mn concentrations. The ferromagnetic Co–Mn exchange interaction is a short-range effect which is only effective at the nearest-neighbor distance. At this distance, the exchange interaction can be further enhanced by a Mn-rich composition, but it might be destroyed by the lattice distortion due to the martensitic transformation.

Influence of interface state in Fe/MgO/Fe magnetic tunnel junction system: C modified interfaces—a first principle study

The Fe/MgO/Fe magnetic tunnel junction with C modified interfaces has been studied based on the first principle density function theory method under a finite bias voltage for thin (five layers) and thick (ten layers) MgO barriers. Positive and negative tunneling magnetic resistance (TMR) ratios are obtained as a function of the interface structure. We found that the tunneling conductance is highly nonlinear for asymmetric systems with C at one side of the barrier, and even a sign reversal of the TMR as a function of the bias was found to be in agreement with experiments.

Structure and magnetic properties of (Nd1−xHox)3Fe23−yCo6Vy compounds

The Ho-substituted (Nd1−xHox)3Fe23−yCo6Vy compounds with x=0–0.9 have been synthesized and their structure and intrinsic magnetic properties have been investigated by x-ray diffraction and magnetic measurements. It is found that all the investigated compounds crystallize in the Nd3(Fe,Ti)29-type structure with monoclinic symmetry and A2/m space group. The unit-cell volume V shows a decreasing tendency with increasing Ho content, reflecting the lanthanum contraction. All the compounds show easy-plan type anisotropy at room temperature. The Curie temperatures Tc are almost independent of the Ho content and the spin reorientation temperature, Tsr, decreases with increasing Ho content from 266 K for x=0 to 127 K for x=0.7. No spin reorientation occurs for x=0.9. The saturation magnetization Ms decreases linearly with increasing Ho content due to the antiferromagnetic coupling between Ho and Nd moments. The anisotropy field Ba increases first, going through a maximum at x=0.5, y=2.0, and then decreases with in...

Effects of rare-earth substitution in : mixed-valence and magnetic properties

The lattice parameters and magnetic properties of (R = Ho, Er) have been investigated. The deviation of the lattice parameters from Vegards law indicates that the Ce valence in both systems fluctuates with the concentration of the dopant R. This fluctuation is directly relevant to the degree of localization of Ce 4f electrons, and is independent of the atomic size of the dopant element. The observed metamagnetic transition of has been analysed from the description in the band picture. The Ce valence fluctuation from the mixed-valence state to the localized state increases the moments of the Ce and Fe ions, and the Curie temperature. The changes in the mixed-valence state also affect the properties of the Ce-Fe coupling.

Anomalous magnetic properties of cerium ions in the compounds (R = Tb, Dy)

The lattice parameters and spontaneous magnetizations of the pseudobinary compounds (R = Tb, Dy) are reported. The analysis of these results revealed the mutability of the Ce 4f ferromagnetism. The change of the degree of delocalization of the Ce 4f electron is used to analyse the changes of the lattice parameter and the spontaneous magnetic moment. A metamagnetic phase transition can be observed for each of the systems investigated, , when the Ce concentration x is about 0.5. The critical phase field increases with the Ce concentration, and the itinerant-electron model has been applied to analyse the tendency towards change of the critical phase field with x.

Structure and anisotropy evolution in the (Nd1−xErx)2Co15.5V1.5 system

Abstract The structure and magnetocrystalline anisotropy of (Nd1−xErx)2Co15.5V1.5 compounds have been investigated by means of X-ray diffraction and magnetic measurements. It is found that the (Nd1−xErx)2Co15.5V1.5 compounds crystallize in the Th2Zn17-type for x⩽0.3 and in the Th2Ni17-type structure for x⩾0.6. Both structures coexist for x=0.4 and 0.5. The Curie temperature shows a slightly decreasing tendency in both structures. The saturation magnetization Ms at 5 K of the (Nd1−xErx)2Co15.5V1.5 compounds decreases monotonically with increasing Er content at a rate of 10.0 μ B / Er . A spin orientation was observed in the compounds with x=0–0.5 and the spin-reorientation temperature decreases with increasing Er content from 448 K for x=0 to 286 K for x=0.5. It is worth noting that the room-temperature magnetocrystalline anisotropy of the (Nd1−xErx)2Co15.5V1.5 compounds changes from easy-cone type for x