Structural and magnetic properties of (Nd 1− xTb x) 3Fe 27.31Ti 1.69 (0⩽ x⩽1.0) compounds

Abstract

The structural and magnetic properties of (Nd 1− x Tb x ) 3Fe 27.31Ti 1.69 compounds have been investigated by means of X-ray diffraction and magnetic measurements. It is found that all compounds with x=0–1.0 retain the Nd 3(Fe,Ti) 29-type of structure and space group A 2/m. Substitution of Tb for Nd leads to a decrease of the lattice constants and the unit-cell volume, reflecting the lanthanide contraction. With increasing Tb content, the Curie temperature T C increases slightly, while the saturation magnetization M s decreases monotonically. The latter can be described in terms of a simple dilution model. At room temperature, the easy magnetization direction of the (Nd 1− x Tb x ) 3Fe 27.31Ti 1.69 compounds depends on the Tb content x and changes from the [4 0 −2] direction for x=0 to the [0 4 0] direction for x=1.0. As the temperature decreases, a spin-reorientation transition is observed at 233 K in the compound Nd 3Fe 27.31Ti 1.69, whereas no spin reorientation is observed in the compounds in which Tb has been substituted for Nd. The anisotropy field B a at room temperature increases with increasing Tb content from 3.0 T for x=0 to 5.2 T for x=1.0. At low temperatures, a first-order magnetization process (FOMP) (of type-II) is observed in Tb 3Fe 27.31Ti 1.69. The critical field B cr of the FOMP decreases monotonically with increasing temperature.