Hydrogenation and anisotropic expansions in R3Fe29-xTx (R = Y, Ce, Nd, Sm,Gd, Tb and Dy; T = V and Cr)

A systematic study of the phase formation, structure and magnetic propertie s of the R3Fe29-xTx compounds (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) has been performed upon hydrogenation. The lattice constants and the unit cell volume of R3Fe29-xTxHy decrease with increasing R atomic number from N d to Dy, except for Ce, reflecting the lanthanide contraction. Regular anis otropic expansions mainly along the a- and b-axis rather than along the c-a xis are observed for all of the compounds upon hydrogenation. Hydrogenation leads to an increase in the Curie temperature and a corresponding increase in the saturation magnetization at room temperature for each compound. Fir st order magnetization processes (FOMP) occur in the external magnetic fiel ds for Nd3Fe24.5Cr4.5H5.0, Tb3Fe27.0Cr2.0H2.8, and Gd3Fe28.0Cr1.0H4.2 compo unds.