The effect of hydrogen on the magnetostriction of rare-earth compounds TbxDy1-xFe2

The crystal structure and the magnetic and magnetoelastic properties of Tbx Dy1-xFe2Hy (x=0.27; 0.41; y less than or equal to3) are investigated. The h ydrides are obtained by the interaction of TbxDy1-xFe2 samples with hydroge n gas at room temperature. It is established that the hydrides have the sam e cubic type of structure as the parent compounds but the lattice parameter in the hydrides is larger than in the hydrogen-free samples. Both the Curi e temperature and the magnetic moment decrease drastically as the hydrogen concentration increases. Measurements of the longitudinal lambda (parallel to) and transverse magnetostriction lambda (perpendicular to) are carried o ut in magnetic fields up to 12 kOe in the temperature range 78-300 K using strain gauges. The thermal expansion coefficients as functions of temperatu re are obtained for hydrides with high hydrogen concentration. The magnetos triction of hydrides is strongly different from that of hydride-free sample s. The small and negative value of the magnetostriction at low temperatures proves that hydrogen atoms make a strong contribution to the crystal field acting on the rare-earth ions. (C) 2001 American Institute of Physics.