High Temperature Properties of Highly Electrical Resistive (Fe 0.81 Co 0.19 ) 84 Ta 9 B 7 Alloy Cast in Air

This paper presents results from in situ X-ray diffraction (XRD), electrical resistivity, and magnetic measurements on an air-cast, amorphous (Fe 0.81 Co 0.19 ) 84 Ta 9 B 7 alloy as a function of temperature. The high temperature magnetic measurements revealed that the Curie temperature of the amorphous phase is 327 °C and crystallization begins at 483 °C. The crystallite sizes determined from the Scherrer analysis of XRD data increased from 13.4 nm at 525 °C to 31.3 nm at 600 °C. XRD data also indicated the presence of two minor metastable phases; one in an as-cast state, which decomposes at temperatures above 400 °C and a second one that starts forming at temperatures above 400 °C and decomposes before the temperature reaches 525 °C. Permeability increased with temperature first, showing a peak value at 125 °C and steadily decreased afterward to values comparable with those of dust cores. Coercivity increased significantly above 200 °C and a peak value of 130 Oe was observed at $\sim 400~^{\circ }\text{C}$ . In the as-cast state, the material exhibited an electrical resistivity value of 180 $\mu \Omega $ -cm, which was significantly reduced after crystallization. The material also exhibited a small negative temperature coefficient of resistivity.