Crystallographic and magnetic properties of NdCo11−xSix compounds

Abstract

The effects of substitution of Si for Co on the crystal structural stability and magnetic properties of NdCo11−xSix compounds have been studied. X-ray diffraction and magnetic measurement show that the single phase region can be expressed as NdCo9.8–9.2Si1.2–1.8 other than NdCo9Si2. X-ray-diffraction study indicates that the compounds adopt the tetragonal BaCd11-type struc- ture. The magnetic properties of a series of NdCo11−xSix solid solutions have been studied by magnetic measurement. Our investigations show that the Curie temperature of NdCo11−xSix increases drastically from 528 K (x=1.8) to 833 K (x=1.2) as the Si content decreases. The Co magnetic moment reaches a maximum between NdCo9.8Si1.2 and NdCo9.6Si1.4, and decreases with the further increase in x. The substitution of Si for Co in NdCo11−xSix leads to a contraction of lattice constant a by 0.2%, c by 0.2%, and a consequent reduction of the unit-cell volume by about 0.6%. The Rietveld refinement results show that the silicon atoms preferentially occupy the 8(d) sites. The occupation of 8(d) sites by proper amount of Si will shift the Fermi level EF upward and to a valley with a lower local density of states in NdCo11−xSix compounds, which is favorable for the stability of the BaCd11-type structure.