Forced Volume Magnetostriction and Induced Moment in GdCo₂

The forced volume magnetostriction, dω/d H , of GdCo 2 has been measured bymeans of a three terminal capacitance dilatometer from 4.2 K up to 328 K. The d o m e g a /d H shows a large negative value at 4.2 K and changes its sign from negative to positive with increasing temperature. This anomalous temperature dependence of dω/d H is ascribed to the volume change associated with the induced moment of Co which depends on the effective field acting on the Co moment. A quantita-tive estimation of dω/d H based upon a molecular field approximation shows an excellent agreement with the experiments. The large value of dω/d H of this system as well as its large spontaneous volume magnetostriction are explained as the volume change caused by the induced moment of the Co atom.