I. Dincer

Giant magnetocaloric effect in the Gd 5 Ge 2.025 Si 1.925 In 0.05 compound

The magnetocaloric properties of the Gd5Ge2.025Si1.925In0.05 compound have been studied by x-ray diffraction, magnetic and heat capacity measurements. Powder x-ray diffraction measurement shows that the compound has a dominant phase of monoclinic Gd5Ge2Si2-type structure and a small quantity of Gd5(Ge,Si)3-type phase at room temperature. At about 270 K, this compound shows a first order phase transition. The isothermal magnetic entropy change (ΔSM) is calculated from the temperature and magnetic field dependences of the magnetization and the temperature dependence of MCE in terms of adiabatic temperature change (ΔTad) is calculated from the isothermal magnetic entropy change and the temperature variation in zero-field heat-capacity data. The maximum ΔSM is −13.6 Jkg−1K−1 and maximum ΔTad is 13 K for the magnetic field change of 0–5 T. The Debye temperature (θD) of this compound is 149 K and the value of DOS at the Fermi level is 1.6 states/eVatom from the low temperature zero-field heat-capacity data. A considerable isothermal magnetic entropy change and adiabatic temperature change under a field change of 0–5 T jointly make the Gd5Ge2.025Si1.925In0.05 compound an attractive candidate for a magnetic refrigerant.

Neutron diffraction study of the magnetic structures of PrMn2-xCoxGe2 (x = 0.4, 0.5 and 0.8) with a new refinement procedure

The magnetic structures of PrMn2−xCoxGe2 (x = 0.4, 0.5 and 0.8) with ThCr2Si2-type structure have been investigated by means of neutron diffraction measurements between 2 and 312 K. We introduced a new refinement procedure to determine the magnetic moments of Pr and Mn sublattices below the rare-earth ordering temperature TCPr because of the overlapping of the magnetic reflections of the Pr and Mn sublattices. Rietveld refinements demonstrated that above the Curie temperature an intralayer antiferromagnetic ordering within (001) Mn layers is observed in PrMn1.6Co0.4Ge2 and PrMn1.5Co0.5Ge2, while the intralayer antiferromagnetic ordering within (001) Mn layers is found over the whole temperature range for PrMn1.2Co0.8Ge2. Below the Curie temperature the PrMn1.6Co0.4Ge2 and PrMn1.5Co0.5Ge2 compounds have a canted ferromagnetic structure with the canting angles 62° and 65° at 2 K, respectively. Below 75 and 70 K, a ferromagnetic ordering of the Pr sublattice is observed along the c-axis for these compounds. Below 70 K, a ferromagnetic ordering of Pr sublattices is found (not detected by magnetic measurements) along the c-axis in PrMn1.2Co0.8Ge2.

Effects of manganese doping on magnetocaloric effect in Ge-rich Gd5Ge2.05Si1.95 alloy

The structure,magnetic and magnetocaloric properties of the Ge-rich Gd5Ge2.05-xSi1.95-xMn2x (x=0.01 and 0.03) alloys were investigated by scanning electron microscopy,X-ray powder diffraction,differential scanning calorimeter (DSC) and magnetization measurements.The results of energy dispersive X-ray analysis (EDX) and X-ray diffraction analyses showed that the composition and crystal structure of the alloys were desired.DSC measurements were performed to determine the transformation temperatures for each alloy.Both alloys exhibited the first order phase transition around room temperature.The alloys showed an anti-ferromagnetic transition around 60 K.The isothermal magnetic entropy changes of the alloys were determined from the isothermal magnetization measurements by using the Maxwell relation.The maximum values of isothermal magnetic entropy change of the Gd5Ge2.05-xSi1.95-xMn2x alloy with x=0.01 was found to be -12.1 and -19.8 J/(kg·K) using Maxwell equation around 268 K in applied fields of 2 and 5 T,respectively.

Magnetic and magnetocaloric properties of Ni43Mn46−xAlxIn11 (x = 0, 0.5 and 1.0)

A nearly parallel G2-manifold Y is a Riemannian 7-manifold whose cone C(Y ) = R>0 × Y has the holonomy group contained in Spin(7). In other words, it is a spin 7-manifold with a real Killing spinor. We have a special class of calibrated submanifolds called Cayley submanifolds in C(Y ). An associative submanifold in Y is a minimal 3submanifold whose cone is Cayley. We study its deformations, namely, Cayley cone deformations, explicitly when it is homogeneous in the 7sphere S.

Fe substitution effect on the magnetic properties of SmMn2?xFexGe2 studied by NMR

We have carried out 55Mn and 149Sm NMR measurements on SmMn2−xFexGe2 (0.05 ≤ x ≤ 0.6) at 4.2 K in order to elucidate the Fe substitution effect on the magnetic properties of SmMn2−xFexGe2. The NMR signals of Mn have been observed in the frequency range 180 – 210 MHz. The resonance frequency plotted against the Fe concentration shows an abrupt change between x = 0.3 and 0.4. This discontinuity suggests that the magnetic structure changes around x = 0.35 in the low temperature range where Sm and Mn sublattices order magnetically.

Effect of heat treatment procedure on magnetic and magnetocaloric properties of Ni43Mn46In11 melt spun ribbons

Abstract The effect of heat treatment on the structural, magnetic and magnetocaloric properties of Ni43Mn46In11 melt-spun ribbons was systematically investigated using X-ray powder diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), magnetic force microscope (MFM) and magnetic measurements. From the XRD studies, tetragonal and cubic phases were detected at room temperature for as-spun, quenched and slow-cooled ribbons. Furthermore, it was observed, upon annealing martensite transition temperatures increased when compared to the as-spun ribbon. To avoid magnetic hysteresis losses in the vicinity of the structural transition region, the magnetic entropy changes-ΔS m of the investigated ribbons were evaluated from temperature-dependent magnetisation-M(T) curves on cooling for different applied magnetic fields. The maximum ΔS m value was found to be 6.79 J kg−1 K−1 for the quenched ribbon in the vicinity of structural transition region for a magnetic field change of 50 kOe.

Coexistence of the canted ferromagnetism and canted antiferromagnetism in La0.6Pr0.4Mn2Si2

24 European Crystallographic Meeting, ECM24, Marrakech, 2007 Page s257 Acta Cryst. (2007). A63, s257 MS38 P01 Effect of monovalent doping in the A site on structural and physical propeties of La1-xCaxMnO3 manganese oxides A. Cheikhrouhou, W. Cheikh-Rouhou Koubaa, A. Mehri, M. Koubaa, Laboratoire de Physique des Matériaux, Faculté des Sciences de Sfax, B. P. 802, 3018 Sfax, Tunisia, Laboratoire Louis NEEL, CNRS, B. P. 166, 38042 Grenoble Cedex 9, France. E-mail: abdcheikhrouhou@yahoo.fr