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 Gd 5 Sb 3 and Gd 5 Bi 3 binaries to yield the Gd 5 Ni 0.96(1) Sb 2.04(1) and Gd 5 Ni 0.71(1) Bi 2.29(1) phases. Both Ni-substituted compounds adopt the orthorhombic Yb 5 Sb 3 -type structure. While the Gd 5 Ni 0.71 Bi 2.29 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 Gd 5 Ni 0.96 Sb 2.04 phase is found to be thermodynamically stable till room temperature. Through annealing at different temperatures, Gd 5 Bi 3 was proven to undergo the Mn 5 Si 3 -type (LT)↔Yb 5 Sb 3 -type (HT) transformation reversibly, whereas Gd 5 Sb 3 was found to adopt only the hexagonal Mn 5 Si 3 -type structure. Orthorhombic Gd 5 Ni 0.96 Sb 2.04 and Gd 5 Ni 0.71 Bi 2.29 and low-temperature hexagonal Gd 5 Bi 3 order ferromagnetically at 115, 162 and 112 K, respectively. In Gd 5 Bi 3 , the ferromagnetic ordering is followed by spin reorientation below 64 K. Magnetocaloric effect in terms of Δ S was evaluated from the magnetization data and found to reach the maximum values of −7.7 J/kgK for Gd 5 Ni 0.96 Sb 2.04 and −5.6 J/kgK for Gd 5 Ni 0.71 Bi 2.29 around their Curie temperatures.