Abstract
The structural and magnetic properties of RFe10.5Mo1.5 alloys and their hydrides were studied using X-ray diffraction and magnetic measurements. Hydrogen occupies the octahedral interstitial 2b site of the tetragonal ThMn12-type structure (space group I4/mmm, Z = 2), which allows a maximum uptake of one hydrogen atom per formula unit. The unit cell volume expands about 1% and the Curie temperature is increased about 10% by the hydrogen uptake. The mean magnetic moment of the iron sublattices is increased. On hydrogenation, (i) the magnetocrystalline anisotropy of the 3d sublattice is enhanced, (ii) in the compounds containing the R elements with a positive second-order Stevens factor αJ, the c-axis is the easy axis, and (iii) for the compounds with R having a negative second-order Stevens factor, the easy direction lies in the ab-plane. The Dy and Tb alloys show temperature induced spin reorientation transitions (SRT). On hydrogen uptake, their hydrides have a basal plane behaviour. This change in the series can be understood by the donor character of H together with a narrowing of the 3d metal bands induced by the volume expansion.
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