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

The structural and magnetic properties of Tm
₂
CrFe
_16-x
Si
_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 Tm
₂
CrFe
_16-x
Si
_x
compounds are in a single phase with the hexagonal Th
₂
Ni
₁₇
-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 Tm
₂
CrFe
_16-x
Si
_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 R
₂
Fe
₁₇
compound can be superposed.