Analysis of heating effects (magnetic hyperthermia) in FeCrSiBCuNb amorphous and nanocrystalline wires

Abstract

The induction heating effects in amorphous and nanocrystalline wires, Fe73.5-xCrxSi13.5Cu1B9Nb3 (x = 3, 7, and 10), are analyzed in this work. In these alloys, the Curie temperature of the amorphous phase, TC, can be tailored through the Cr content of the alloy or the volume crystalline fraction after nanocrystallization. Four samples were selected; amorphous with x = 0 and 10 and nanocrystalline x = 7 with different crystalline fractions. The Curie temperature of the residual amorphous phase, TCa, was experimentally determined by the temperature dependence of the self-inductance of the samples. The analysis of the frequency dependence of the complex magnetic susceptibility enabled the estimation of the magnetic power losses in the samples. The heating effects on the wires were analyzed under the application of an ac magnetic field employing a home-made hyperthermia set-up. A single piece of a wire was immersed in a water bath (initial temperature from 291 K to 325 K) and subjected to the ac magnetic field. The specific absorption rate (SAR) was estimated through the initial slope of the temperature increase as a function of time. Maximum SAR values were obtained in the amorphous sample (x = 3) with the highest TC and enhanced magnetic power losses. In the nanocrystalline samples (x = 7), the detected heating effects above TCa are interpreted as a consequence of the magnetization process of the ferromagnetic grains. However, in spite of the low SAR displayed by the amorphous wire with TC ≈ 300 K (x = 10), interesting self-regulated characteristics are observed in this sample.