In the present work we report on the structural and magnetic behaviors of the PrNi 5−x Co x intermetallic compounds. Due to the competition between the anisotropy energies of both Co and Pr sublattices, this series has a spin-reorientation phenomenon at low temperature ͑140 K͒. The Curie temperature, as a function of Co content, has a sudden increase above a critical concentration x c ϳ 1.9 and this feature is assigned as a percolation of geometrically spaced Co clusters. This assumption is explained based on the critical exponent of percolation theory. The series presents therefore a rich magnetic phase diagram, which could be established over a full doping range, i.e., from x =0 to x = 5. We have also studied these compounds on the magnetocaloric point of view and found a quite large full width at half maximum ͑␦T FWHM ͒ of the magnetic entropy change curves for some of the compositions, due to the merging of the ⌬S peaks associated with the spin-reorientation process and the Curie temperature T C . In addition, the series has an appreciable relative cooling power, which is therefore suitable to be used in a magnetic refrigerator operating in a large range of temperature.

We explored the Fe rich side of the (Mn,Fe) 2 (P,Ge) magnetocaloric system. The transition temperature of this system is extremely easy to tune with careful manipulation of Fe and Ge content as well as stoichiometrical proportions, which gives rise to the real possibility of lowering the price of this compound and thus make it economically viable for practical magnetocaloric applications. Novel and unexpected magnetic properties observed in this system suggest an exciting potential for permanent magnet application in a limited concentration range.

Conventional and anisotropic magnetocaloric effects were studied in cubic rare earth RNi 2 ͑R =Nd,Gd,Tb͒ ferromagnetic intermetallic compounds. These three compounds are representative of small, null, and large magnetocrystalline anisotropy in the series, respectively. Magnetic measurements were performed in polycrystalline samples in order to obtain the isothermal magnetocaloric data, which were confronted with theoretical results based on mean field calculations. For the R = Tb case, we explore the crystalline electrical-field anisotropy to predict the anisotropic magnetocaloric behavior due to the rotation of an applied magnetic field of constant intensity. Our results suggest the possibility of using both conventional and anisotropic magnetic entropy changes to extend the range of temperatures for use in the magnetocaloric effect.

A comparison of different nominal LuMnO3 ceramics exposes pertinent structural and magnetic property variations due to subtle self-doping effects.