Magnetic properties of Th3P4-type Tb4Sb3−X{Si, Ge, Bi}X solid solutions

The magnetic properties of Tb4Sb2Bi, Tb4Sb2.75Ge0.25 and Tb4Sb2.3Si0.7 solid solutions (Th3P4-type, cubic; cI28, space group I4¯3d, No. 220) have been investigated by means of magnetization and neutron diffraction studies. The magnetization measurements indicate that the Tb4Sb2Bi compound orders magnetically at 120K (TN) and 50K (TC). The magnetization vs. field isotherm at 5K shows signature of ferromagnetic order. Neutron diffraction experiment in zero applied magnetic field shows that below TN=125(4)K Tb4Sb2Bi exhibits a antiferromagnetic flat spiral type ordering with wave vector K1=[±KX,±KX,±KX] (KX value changes from 0.1033 up to 0.158 in the temperature interval down to 2K). Below Tm=70(4)K the decreasing of antiferromagnetic component coincides with increasing of the ferromagnetic component and about TCN=55(4)K, Tb4Sb2Bi shows ferromagnetic transition. At 2K, the magnetic structure of Tb4Sb2Bi is ferromagnetic cone and the cone axis is along [111] direction.Neutron diffraction study of Tb4Sb2.75Ge0.25 indicate an antiferromagnetic ordering at 155(4)K (ferromagnetic cone with K1=[±0.136(2), ±0.136(2), ±0.136(2)]) and ferromagnetic ordering (sharp increasing of ferromagnetic component) at 145(4)K. The KX value is nearly constant from 155K down to 2K. At 2K, the magnetic structure of Tb4Sb2.75Ge0.25 is ferromagnetic cone with a weak antiferromagnetic component and the cone axis is along [111] direction.Low field magnetisation measurements on Tb4Sb2.3Si0.7 indicate a ferromagnetic ordering at TC∼180K. Thus small substitutions of Bi, Ge and Si at Sb-site of Tb4Sb3 are found to increase the magnetic ordering temperature of the parent compound.