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Magnetic, magnetocaloric, and magnetoresistance studies have been carried out on polycrystalline samples of Laves phase compounds Ho͑Ni 1−x Fe x ͒ 2 ͓x = 0, 0.05, and 0.1͔. The magnetocaloric effect in HoNi 2 is found to be maximum near the ordering temperature with values of 7 J mol −1 K −1 and 10.1 K for the isothermal magnetic entropy change and the adiabatic temperature change, respectively, for a field of 50 kOe. With Fe substitution, the temperature variation of magnetocaloric effect shows an additional peak at low temperatures, which is much more pronounced than the peak at the ordering temperature. The origin of the low temperature peak is attributed to the field-induced metamagnetic transition. The magnetoresistance data also seem to support the occurrence of the metamagnetic transition.

A systematic study has been made on the effect of Fe substitution by means of resistivity, thermal conductivity, and Seebeck coefficient of the Mg 1−x Fe x B 2 superconductor involving 0%, 0.3%, 0.6%, 1.2%, and 3.0% Fe content. The superconducting transition has been found to be very sharp ͑ϳ0.2 K͒ for a pristine sample and substitution of Fe results in the decrease of T C with the increase in the transition width. Thermal conductivity is found to decrease with Fe content in general, such that the shoulder present in the pristine sample tends to fade away with increasing Fe. An analysis has been made on the normal state resistivity in terms of a two-band model, and of the thermal conductivity in terms of the Wiedemann-Franz law and the lattice thermal conductivity, and the information obtained on the basis of this analysis has been discussed. Besides, the electronic density of states ͑DOS͒ near the Fermi level remains nearly unaffected upon Fe substitution, as evidenced by the Seebeck coefficient measurements. When compared with Mn, Fe behaves like a nonmagnetic element with a modest variation in T C and on the other hand, the T C depression is much stronger when compared with other elements like Al, Cu, etc. Therefore, the observed variation in T C for the presently investigated concentrations of Fe is attributed to the specific nature of the given substituent element ͑Fe͒ in altering the phonon frequency and/or electron-phonon coupling strength rather than spin-flip scattering or change in DOS or disorder.

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Magneto-transport and magnetic studies carried out on the (1−x)Pr2/3Ba1/3MnO3+xAg2O (x = 0–30 mol%) composite system are reported here. Two transitions (TP1 and TP2) are observed in the electrical resistivity of the pristine Pr2/3Ba1/3MnO3 (PBMO) system. With addition of Ag2O electrical resistivity decreases. While TP1 gets sharper, TP2 disappears with increasing Ag2O content. Electrical resistivity fitting below TP2 indicates that PBMO exhibits a crossover from a spin dependent scattering-like polycrystalline material to a single crystalline material in composites. Low temperature resistivity upturn, which results from the combined effect of weak localization, electron–electron and electron–phonon scattering mechanisms, also decreases in the composite materials. The enhanced intrinsic magneto-resistance seen in the composite system has been ascribed to factors like decrease in electrical resistivity due to the formation of metallic Ag from Ag2O dissociation, disorder reduction, magnetic inhomogeneity and growth of spin clusters. The monotonic decrease in the extrinsic magneto-resistance due to Ag is found to be related to the disappearance of the energy barrier formed at the grain boundary. The observed decrease in the magnetization below the Curie temperature (TC) is considered vis-à-vis the magnetic volume reduction and the non-magnetic Ag acting as a pinning centre to the domain rotation.