Temperature-Dependent Magnetic Properties of Magnetically Biphase Microwires

The magnetic behaviour of soft/hard biphase magnetic microwires has been studied as a function of temperature in the range 25°C to 900°C. The microwires consist of an ultrasoft CoFe-based vanishing magnetostriction amorphous core covered by insulating Pyrex coating prepared by quenching and drawing, plus an electroplated CoNi magnetically harder external shell. The magnetization process has been analyzed through the study of the hysteresis loops and their parameters like saturation magnetization and coercivity of the different phases, measured in a vibrating sample magnetometer. The magnetically biphase character has been first confirmed by room-temperature measurements for wires with different thickness. The observed dependence of magnetization and coercivity on temperature is correlated with the overcoming of the Curie temperature and crystallization of the amorphous soft core.