The effect of hydrogen on the thermal expansion and magnetostriction of RFe/sub 11/Ti intermetallic compounds

Thermal expansion and its anomalies at magnetic spin-reorientation phase transitions on single crystals of the tetragonal rare-earth intermetallics RFe/sub 11/Ti (R = Y, Sm, Tb, Dy, Ho, Er, and Lu) are investigated by the tensometric method in the temperature range 77400 K. The temperature dependences of the thermal expansion coefficient (alpha)(T) are obtained. It is found that the YFe/sub 11/Ti and LuFe/sub 11/Ti compounds with uniaxial magnetic anisotropy exhibit pronounced anomalies in the (alpha)(T) at T = 180 and 265 K. The hydrogenation shifts the observed anomalies toward lower temperatures. There are no noticeable anomalies in (alpha)(T) for DyFe/sub 11/Ti. Hydride ErFe/sub 11/TiH exhibits additional anomalies in (alpha)(T) associated with the process of the hydrogen ordering in the ThMn/sub 12/-type crystal lattice. Hydrogenation leads to change of the magnetostriction constant (lambda)/sub 2//sup (alpha),2/ sign.