Thermodynamics and magnetism of selected complex intermetallic compounds and their hydrides

Many complex intermetallic compounds exhibit a large chemical affinity and solubility for hydrogen. Accompanying hydriding the physical properties (structural, thermodynamic, magnetic, etc.) of the compounds significantly differ from those of the parent intermetallics. In the present investigation, the following systems were studied: ZrMn{dollar}sb2{dollar}, ZrCrFe and ZrVCo; ZrMn{dollar}sb2{dollar}T{dollar}sb{lcub}0cdot8{rcub}{dollar} (T = Fe, Co, Ni and Cu); R{dollar}sb2{dollar}Fe{dollar}sb{lcub}14{rcub}{dollar}B (R = Gd, Tb, Dy, Ho and Er) and R{dollar}sb2{dollar}Co{dollar}sb{lcub}14{rcub}{dollar}B (R = La, Pr, Nd, Sm, Gd, Tb and Y).; For the isoelectronic series of alloys all of the host alloys and hydrides crystallize in the C14 type structures. Pressure-composition isotherms (PCIs) were determined. The standard thermodynamic quantities were derived from the measured PCIs and from calorimetric measurements.; Magnetic properties have been investigated for hyperstoichiometric systems and their hydrides. Hydrogenation is accompanied by a large expansion in unit cell volume. Hydrogenation enhances magnetism in all cases. The systems exhibit susceptibility behavior. Unusual history-dependent magnetic behavior was observed for hydrides below 80 K.; R{dollar}sb2{dollar}Fe{dollar}sp{lcub}14{rcub}{dollar}B systems were hydrogenated. The pressure-composition isotherms (PCIs) of hydrides showed only a solid solution behavior between room temperature and 300 C and at pressures down to 10{dollar}sp{lcub}-2{rcub}{dollar} atm. The absorbed hydrogen leads to an increase in unit cell volume, without a change in crystal structure. Saturation magnetization, M{dollar}sb{lcub}rm s{rcub}{dollar}, and magnetic ordering temperature, T{dollar}sb{lcub}rm c{rcub}{dollar}, were enhanced upon hydrogenation. In all cases the anisotropy fields were significantly reduced by hydrogen absorption. Hydrogen induces spin-reorientation effect in the Gd- and Dy-based compounds, while it has a marked influence in raising the spin-reorientation temperature, T{dollar}sb{lcub}rm SR{rcub}{dollar}, in the Er{dollar}sb2{dollar}Fe{dollar}sb{lcub}14{rcub}{dollar}B compound. The spin-reorientation phenomena observed for Gd{dollar}sb2{dollar}Fe{dollar}sb{lcub}14{rcub}{dollar}BH{dollar}sb{lcub}rm x{rcub}{dollar} suggest that there is competition among the 6 Fe sublattices in regard to the sign and temperature coeficient of anisotropy.; For the R{dollar}sb2{dollar}Co{dollar}sb{lcub}14{rcub}{dollar}B systems, the pressure-composition isotherms of the hydrides exhibit some indication of a plateau pressure region at high hydrogen content. Introduction of hydrogen expands the unit cell volume without a change in crystal structure. In contrast to the Fe analogs M{dollar}sb{lcub}rm s{rcub}{dollar}, was decreases upon hydrogenation. For Nd{dollar}sb2{dollar}Co{dollar}sb{lcub}14{rcub}{dollar}B, the host alloy exhibits two spin reorientation transition temperatures. For R{dollar}sb2{dollar}Co{dollar}sb{lcub}14{rcub}{dollar}B with R = Pr, Tb and Nd, hydrogen decreased T{dollar}sb{lcub}rm SR{rcub}{dollar}. In all cases the anisotropy fields were significantly reduced by hydrogen absorption. (Abstract shortened with permission of author.)...