GIANT VOLUME MAGNETOSTRICTION IN THE FERH ALLOY

In a search for high-magnetostrictive materials we have discovered in FeRh a large induced volume magnetostriction (almost-equal-to 0.82%) a t and above room temperature. Thermal-expansion measurements performed on the ordered CsCl crystallographic structure of FeRh in the tempera ture range 250-800 K reveal Invar-like behavior at T(c) = 680 K associ ated with a paramagnetic-ferromagnetic second-order phase transition. At T(F-AF) = 405 K, a large contraction of the lattice within the ferr omagnetic (F) phase takes place through a first-order transformation r esulting in a low-volume, low-temperature antiferromagnetic phase (AF) (anti-invar-like behavior). At moderate fields above room temperature and within the AF phase, we have found a giant value for the volume m agnetostriction of omega = 8.2 X 10(-3). These results constitute evid ence for the existence of the theoretically predicted metastable F pha se (high-volume state) within the AF phase which can be reached by an applied magnetic field. The present experiments offer additional persp ectives on an old problem in magnetism and suggest potential applicati ons of this alloy as a high-magnetostrictive material.