The Crystal Structure and Magnetic Property of Bi-substituted Nd_2Fe_(17-x-y)Ti_xSi_y Intermetallic Compounds

摘要

The synergetic effects of the substitution of Ti and Si for Fe on the crystallographic structure and magnetic properties of Nd_2Fe_(17-x-y)Ti_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 Th_2Zn_(17)-type structure. For a given Ti content, the a-axis and the unit cell volume V of Nd_2Fe_(17-x-y)Ti_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 Nd_2Fe_(16.5-y)Ti_(0.8)Si_y and Nd_2Fe_(16.5-y)Ti_(0.5)Si_y is higher than that of singly substituted Nd_2Fe_(16-y)Si_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 Nd_2Fe_(17-x-y)Ti_xSi_y compounds increases with increasing Si content and the Ms first increases and then decreases. The Ms of Nd_2Fe_(17-x-y)Ti_xSi_y decreases with the increase of Ti content.