MAGNETOVOLUME EFFECTS IN NONMETALLIC CENISN

Volume thermal expansion and magnetostriction experiments performed on a CeNiSn single crystal down to 0.1 K in fields up to 8 T are reporte d. The Gruneisen parameter Gamma changes sign from positive to negativ e around 1 K. This effect might be attributed to a competition between a gap opening and a normal heavy-fermion behaviour. The latter is rap idly restored in a magnetic field: in 8 T, Gamma increases regularly o n cooling up to a value close to 45 at 0.1 K.