Structural and Magnetic Properties of ${\hbox {Tm}}_{2}{\hbox {CrFe}}_{16-x}{\hbox {Si}}_{x}$ Compounds

The structural and magnetic properties of Tm₂CrFe_16-xSi_x (x=0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) compounds are investigated by means of X-ray diffraction and magnetization measurements. The results show that the Tm₂CrFe_16-xSi_x compounds are in a single phase with the hexagonal Th₂Ni₁₇-type structure. The lattice parameters a and c and the unit-cell volume v decrease monotonously with x increasing. The Curie temperature T_C increases initially (x <; 1.5) with x increasing, followed by a decrease at higher concentrations (x >; 1.5) . There is a maximum of the Curie temperature, which is about 450 K, at x=1.5. Spin reorientations are observed in the temperature dependences of the magnetization of Tm₂CrFe_16-xSi_x compounds. The spin reorientation temperature (T_sr) increases from 144 K at x=0 to 259 K at x=3.0 with x increasing. This means that the Si atoms substituting for Fe atoms can increase obviously the easy-axis magnetocrystalline anisotropy. The analysis shows that the effect of Cr substitution and the effect of Si substitution on the Curie temperature and the magnetocrystalline anisotropy of R₂Fe₁₇ compound can be superposed.