New aspects of magnetocaloric effect in NiMn sub(0.89)Cr sub(0.11)Ge

Investigations of structural and magnetic phase transitions in the NiMn sub(0.89)Cr sub(0.11)Ge half-Heusler alloy were carried out by DSC, XRD (80-400 K), magnetic susceptibility and magnetization (1.9-400 K, magnetic field up to 9.0 T, pressure up to 5.25 kbar) measurements. At high temperatures the sample is a single phase crystallizing in the hexagonal crystal structure (Ni sub(2)In-type, space group P6 sub(3)/mmc) while below 260 K, down to 100 K, some amount of the hexagonal phase coexists with the orthorhombic (TiNiSi-type, space group Pnma) one. Strong magnetostructural coupling is observed. Magnetic data indicate that with increasing temperature magnetic properties of the sample change from antiferro- to ferro- and then to paramagnetic ones. The latter magnetic phase transition is associated with the crystal structure change and results in large magnetic entropy change equal to -51 J/kg K at mu sub(o)H = 9.0 T near 260 K. Application of external pressure shifts T sub(c) towards lower temperatures.