Gd5Ni0.96Sb2.04 and Gd5Ni0.71Bi2.29: Crystal structure, magnetic properties and magnetocaloric effect. Structural transformation and magnetic properties of hexagonal Gd5Bi3

Nickel was successfully introduced into the Gd5Sb3 and Gd5Bi3 binaries to yield the Gd5Ni0.96(1)Sb2.04(1) and Gd5Ni0.71(1)Bi2.29(1) phases. Both Ni-substituted compounds adopt the orthorhombic Yb5Sb3-type structure. While the Gd5Ni0.71Bi2.29 phase is thermodynamically stable at 800 °C and decomposes at lower temperatures upon annealing, it can be easily quenched to room temperature by rapid cooling from 800 °C. The Gd5Ni0.96Sb2.04 phase is found to be thermodynamically stable till room temperature. Through annealing at different temperatures, Gd5Bi3 was proven to undergo the Mn5Si3-type (LT)↔Yb5Sb3-type (HT) transformation reversibly, whereas Gd5Sb3 was found to adopt only the hexagonal Mn5Si3-type structure. Orthorhombic Gd5Ni0.96Sb2.04 and Gd5Ni0.71Bi2.29 and low-temperature hexagonal Gd5Bi3 order ferromagnetically at 115, 162 and 112 K, respectively. In Gd5Bi3, the ferromagnetic ordering is followed by spin reorientation below 64 K. Magnetocaloric effect in terms of ΔS was evaluated from the magnetization data and found to reach the maximum values of −7.7 J/kgK for Gd5Ni0.96Sb2.04 and −5.6 J/kgK for Gd5Ni0.71Bi2.29 around their Curie temperatures.