Structural and magnetic properties of Nd 3(Fe 1− xCo x) 27.7Ti 1.3 (0< x≤0.4) alloys

Abstract

Structural and magnetic properties of a novel series of intermetallic compounds, with nominal stoichiometry Nd 3(Fe 1− x Co x ) 27.7Ti 1.3 (0< x≤0.4) are presented. The samples crystallise in the Nd 3(Fe,Ti) 29-type structure with monoclinic symmetry (space group A2/m). The unit cell volume is decreasing as the Co content increases; the cell parameters show anisotropic decrease with the Co content. The Curie temperature increases monotonically with x from 437 to 878 K and the room temperature saturation magnetisation increases from 143.3 for x=0 to 172.5 Am 2/kg for x=0.3 and remains practically the same for x=0.4. For x=0 and 0.1 a tilted magnetic structure is observed. For x≥0.2 the compounds present an easy-magnetisation direction along the [4 0 −2] direction. Ac susceptibility curves in the whole range of the Co content ( x=0–0.4) reveal a broad transition at about 160 K, whereas for x=0–0.2 a sharp one with the corresponding transition temperature decreasing with increasing Co content. The observed changes of the critical temperatures observed in the ac susceptibility curves and the obtained anisotropy field values are related to the change of the magnetic anisotropy at x=0.2. The average hyperfine field values depend on the Co content in a way similar to the dependence of the saturation magnetisation.