Structure and magnetic properties of R 2(M, Ni) 14B pseudoternary compounds (R ≡ Nd, Pr; M ≡ Fe, Co)

Abstract

The melting behaviour, solid state phase transformations, structure and magnetic properties of pseudo-ternary compounds Nd 2(Fe 1 − x Ni x ) 14B and Pr 2(Co 1 − y Ni y ) 14B have been studied using differential thermal analysis, optical microscopy, X-ray diffraction, electron probe micro-analysis and magnetic measurements. It was found that the Curie temperature of Nd 2(Fe 1 − x Ni x ) 14B increased with increasing x up to x = 0.2, however the saturation magnetization behaved in an opposite way. In the case of Pr 2(Co 1 − yNi y) 14B, the Curie temperature decreased with increasing y up to y = 0.2. The magnetic phase transition occurring at a temperature between room temperature and Curie temperature is believed to be associated with spin reorientation. The magnetic phase transition temperature is lowered by nickel substitution. At high temperature, eutectoid decomposition R 2(Ni, M) 17 → R(Ni, M) 5 + α-Ni(M) takes place in these two pseudo-ternary compounds in the composition ranges x = 0.6 – 1.0 and y = 0.3 – 1.0 respectively. When x( y)⩽0.2, both Nd 2(Fe 1 − x Ni x ) 14B and Pr 2(Co 1 − y Ni y ) 14B are single phase with a tetragonal structure. The phase constituents of these two systems at room temperature are triplex in the composition range 0.3⩽ x( y)⩽1.0.