Negative Thermal Expansion of Tm2Fe15SiCr compound

The thermal expansion and the Curie temperature of Tm2Fe15SiCr compound have been investigated by means of x-ray diffraction and magnetization measurements. The result shows that the Tm2Fe15SiCr compound has a hexagonal Th2Ni17-type structure. One Cr and one Si atoms substituting for two Fe atoms can increase the Curie temperature obviously. In magnetic state, an anisotropic anomalous thermal expansion was observed. Along the c-axis, the average linear thermal expansion coefficient alpha(c)=-2.04x10(-5)/K in the temperature range 303-460K. Along the a-axis, the average linear thermal expansion coefficient alpha(a)=-8.09x10(-5)/K in 370-410K. In the temperature range 370-450K, the average volume thermal expansion coefficient alpha(v) =-2.08x10(-5)/K. The mechanism of the thermal expansion anomaly of Tm2Fe15SiCr compound was discussed in this paper.