The effect of hydrogen on the thermal expansion and magnetostriction of RFe11Ti intermetallic compounds

Thermal expansion and its anomalies at magnetic spin-reorientation phase transitions on single crystals of the tetragonal rare-earth intermetallics RFe₁₁Ti (R = Y, Sm, Tb, Dy, Ho, Er, and Lu) are investigated by the tensometric method in the temperature range 77-400 K. The temperature dependences of the thermal expansion coefficient α(T) are obtained. It is found that the YFe₁₁Ti and LuFe₁₁Ti compounds with uniaxial magnetic anisotropy exhibit pronounced anomalies in the α(T) at T = 180 and 265 K. The hydrogenation shifts the observed anomalies toward lower temperatures. There are no noticeable anomalies in α(T) for DyFe₁₁Ti. Hydride ErFe₁₁TiH exhibits additional anomalies in α(T) associated with the process of the hydrogen ordering in the ThMn₁₂-type crystal lattice. Hydrogenation leads to change of the magnetostriction constant λ₂^α,2 sign.