THERMODYNAMIC STUDY OF THE MAGNETIC-ORDERING OF FE3-XMNXSI ALLOYS

The compounds Fe3-xMn(x)Si exhibit a complex magnetic behavior for 0.6 less-than-or-equal-to x less-than-or-equal-to 1.75 involving ferromagnetic ordering followed by a reordering at lower temperature. Measurements of the thermal expansion alpha and the specific heat C(p) show only a weak anomaly at the Curie temperature, T(C), whereas a large, relatively sharp peak occurs at the magnetic reordering temperature, T(R). Thermal expansion measurements for the Fe2.2Mn0.8Si compound made about T(R) are indicative of long-range ordering that can be suppressed in an applied field of approximately 0.4 T. Magnetization measurements show that low fields, 1-2 mT, strongly influence the bulk magnetization. Irreversible magnetization behavior, similar to that in spin-glass systems, is displayed.