Magnetic order of the La3NiGe2-type Tb3NiSi2

The novel Tb3NiSi2 phase adopts the La3NiGe2-type structure (Pnma, N 62, oP24). According to the thermal dependence of the magnetization measurements in 100Oe applied field, Tb3NiSi2 undergoes a ferromagnetic-like transition at 135K and a spin-orientation transition at 53K. Based on the neutron diffraction studies in a zero applied field, Tb3NiSi2 shows four types of mixed ferromagnetic–antiferromagnetic ordering below ~130K, 82K, 66K and 53K. The unit cell of Tb3NiSi2 undergoes an isotropic compression down to 143K and an anisotropic one below the temperature of the ferromagnetic transition at ~130K: the a cell parameter increases, whereas the b and c cell parameters and unit cell volume decrease with the decreasing temperature. At 1.5K the terbium magnetic moment reaches the value 9.1(1)μB.