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Hydrides of LaFe11.57Si1.43 intermetallic compound have been prepared by high-energy ball milling in the presence of hydrogen gas, a process known as reactive milling. The Curie temperature of the samples was tuned within the temperature range of 199 K to 346 K by changing the hydrogen content from 0 to 2.3 at. % without compromising much of the magnitude of the magnetocaloric effect. Arrott plots and large hysteresis in the magnetization vs magnetic field curves confirm that the first-order itinerant-electron metamagnetic transition is the reason for large entropy change in the parent as well as in the hydride samples. The present study indicates that reactive milling can be an effective method for incorporating interstitial hydrogen within these compounds in order to raise their TC to room temperature.

We discuss a series of thermodynamic, magnetic, and electrical transport experiments on the two heavy fermion compounds CeNi 2 Ge 2 and YbRh 2 Si 2 in which magnetic fields, B, are used to tune the systems from a non-Fermi liquid (NFL) into a field-induced FL state. Upon approaching the quantumcritical points from the FL side by reducing B we analyze the heavy quasiparticle (QP) mass and QP-QP scattering cross sections. For CeNi 2 Ge 2 the observed behavior agrees well with the predictions of the spin-density wave (SDW) scenario for three-dimensional (3D) critical spin-fluctuations. By contrast, the observed singularity in YbRh 2 Si 2 cannot be explained by the itinerant SDW theory for neither 3D nor 2D critical spinfluctuations. Furthermore, we investigate the magnetization M(B) at high magnetic fields. For CeNi 2 Ge 2 a metamagnetic transition is observed at 43 T, whereas for YbRh 2 Si 2 a kink-like anomaly occurs at 10 T in M vs B (applied along the easy basal plane) above which the heavy fermion state is completely suppressed.KEY WORDS : heavy fermion; magnetic field; CeNi 2 Ge 2 ; YbRh 2 Si 2 .

Magnetocaloric effect (MCE) in low-cost iron-based binary alloys R2Fe17 (R = Y, Pr) has been investigated by measuring their magnetic properties. The Curie temperature of these alloys is found to be close to room temperature. The specific heat measurement of these materials indicates a second order ferromagnetic/paramagnetic phase transition. The MCE properties in these alloys are comparable to that of gadolinium, which is very expensive for domestic use. Therefore these binary alloys are suitable as room temperature MCE materials. The effect of pulsed magnetic field on the MCE properties has also been studied up to 25 T.

Amorphous states have been found in rapidly quenched alloys in the pseudoternary system DyMn6−x−yFex+yGe6−xAlx (x,y=0 to 6). The amorphous state is formed in competition to the crystallization of ternary (1-6-6 rare earth-transition metal-metal) compounds. The melt-spun ribbons were investigated by x-ray diffraction, high resolution transmission electron microscopy, differential scanning calorimetry, and magnetization measurements. All amorphous samples exhibit multistep crystallization behavior without a clear indication for a glass transition below the first exothermic effect. Some of the amorphous alloys exhibit a magnetic ordering above room temperature and complex magnetic transitions similar to the properties of crystalline 1-6-6 compounds.