The Crystal Structure and Magnetic Property of Bi-Substituted Nd2Fe17-x-yTixSiy Intermetallic Compounds

The synergetic effects of the substitution of Ti and Si for Fe on the crystallographic structure and magnetic properties of Nd₂Fe_17-x-yTi_xSi_y compounds have been comprehensively investigated by means of x-ray diffraction, neutron diffraction and magnetic measurements. Rietveld refinements of the diffraction data indicate that all the samples crystallize in the rhombohedral Th₂Zn₁₇-type structure. For a given Ti content, the a-axis and the unit cell volume V of Nd₂Fe_17-x-yTi_xSi_y decrease linearly with increasing silicon content, while the c-axis behaves complicatedly dependent on different Ti content. The site occupancies of Ti and Si in the crystallographic sites significantly change compared to what is observed in the corresponding singly substituted compounds. The T_C of doubly substituted Nd₂Fe_16.5-yTi_0.8Si_y and Nd₂Fe_16.5-yTi_0.5Si_y is higher than that of singly substituted Nd₂Fe_16-ySi_y for a lower Si content while the converse behavior is observed for a higher Si content. For a given Ti content, the T_C of Nd₂Fe_17-x-yTi_xSi_y compounds increases with increasing Si content and the M_s first increases and then decreases. The M_s of Nd₂Fe_17-x-yTi_xSi_y decreases with the increase of Ti content.