Mo2NiB2-type Sm2Co2Al and Sm2Co2Ga compounds: Magnetic properties and giant low-temperature coercivity.

The magnetic ordering of Mo 2 NiB 2 -type Sm 2 Co 2 Al and Sm 2 Co 2 Ga ( Immm , No. 71, oI 10) compounds has been established using bulk magnetic measurements. Polycrystalline Sm 2 Co 2 Al and Sm 2 Co 2 Ga undergo ferromagnetic transitions (T C ) at 50 K and 62 K, respectively, and low-temperature field induced transitions (T m ) around 14 K and 16 K (in a field of 10 kOe), respectively. Between T C and T m Sm 2 Co 2 Al and Sm 2 Co 2 Ga are soft ferromagnets. Below T m Sm 2 Co 2 Al and Sm 2 Co 2 Ga exhibit permanent magnet properties with a residual magnetization per samarium of 0.38 μ B and 0.36 μ B , respectively, and a large coercive field of 69 kOe and 72 kOe, respectively, at 5 K. The magnetocaloric effects of Sm 2 Co 2 Al and Sm 2 Co 2 Ga were calculated in terms of isothermal magnetic entropy change and they reach maximum values of −1.62 J/kg K and −1.31 J/kg K for a field change of 50 kOe at 50 K and 58 K, respectively. Low temperature magnetic ordering with enhanced anisotropy in Sm 2 Co 2 Al and Sm 2 Co 2 Ga is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +1.63 J/kg K and +1.06 J/kg K for a field change of 50 kOe at 10 K and 8 K, respectively. [ABSTRACT FROM AUTHOR]