New aspects of magnetocaloric effect in NiMn0.89Cr0.11Ge

• # Pnma below 210 K, # P63/mmc above 260 K, for 210 K • Magnetic transitions from antiferro- to ferro- and to paramagnetic phase detected.
• Significant magnetocaloric effect observed about 260 K at ambient pressure.
• Magnetostructural effect observed at 260 K (ΔV/V= 2.4%) at ambient pressure.
• Magnetic measurements under hydrostatic pressure up to 5.25 kbar; (p, T) diagram.

Investigations of structural and magnetic phase transitions in the NiMn0.89Cr0.11Ge 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 (Ni2In-type, space group P63/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 μ0H= 9.0 T near 260 K. Application of external pressure shifts TC towards lower temperatures.