Low Working Temperature Near Liquid Helium Boiling Point Of Rnial2 (R=Tm, Tb And Gd) Compounds With Large Magnetocaloric Effect

A polycrystalline TmNiAl2 compound with transition temperature near the liquid helium boiling point was successfully synthesized. Magnetic measurements show that FM (ferromagnetic) to FM and FM to PM (paramagnetic) transitions take place at 2.4K and 4.0K, respectively. Magnetic entropy change (-S-M) is calculated, and its maximal value [(-S-M)(max)] reaches as high as 20.7J/kgK with the field change of 0-5T. The low transition temperature together with large (-S-M)(max) at the liquid helium temperature zone originates from the weak spin-spin exchange interaction between Tm atoms. For a clear comparison, the magnetocaloric effect (MCE) of polycrystalline RNiAl2 (R=Tb and Gd) samples was also prepared and investigated. For the TbNiAl2 compound, FIM (ferrimagnetic) to AFM (antiferromagnetic) and AFM to PM transitions occur at 11.0K and 21.5K, respectively. As for the GdNiAl2 compound, an FM to PM transition occurs at 30.5K. The value of (-S-M)(max) under the field change of 0-5T is calculated to be 11.8J/kgK and 17.3J/kgK for TbNiAl2 and GdNiAl2, respectively. Compared with other RNiAl2-series MCE materials, TmNiAl2 exhibits the lowest working temperature and relatively larger (-S-M)(max). The large MCE at low temperature indicates that TmNiAl2 is competitive among the MCE materials working at a liquid helium temperature zone.