The Curie temperature, TC, of a-Fe90-xCoxSc10 was determined using both mean field theory and Landau’s theory of second-order phase transitions in zero and non-zero external fields. The value of TC of a- Fe5Co85Sc10, determined by the above theoretical approaches is 1150 K, which is the highest TC ever measured for amorphous alloys. The flattening of the measured normalized magnetization, M(T)/M(0), as a function of the reduced temperature, T/TC, is explained within the framework of the Handrich- Kobe model. According to this model the fluctuation of the exchange integral is the main reason for the flattening of M(T)/M(0). In the case of a-Fe90Sc10 without Co, however, the fluctuation of the exchange integral isdominant only at zero external field, Bex=0. In contrast to other ferromagnetic alloys, where the flattening of M(T)/M(0) is characteristic for an amorphous structure, the a- Fe5Co85Sc10 does not exhibit any trace of the fluctuation of the exchange integral.
Y. Fang, M. Ghafari, T. Feng, et al., Scientific Reports, 2018, accepted.
The addition of Co content in Fe90-xCoxSc10 (x = 1, 3, 5 and 7) can not only tune the Curie temperature of these alloys to room temperature, but also simultaneously increase the maximum value of the magnetic entropy change (−ΔSMpk). The −ΔSMpk is 1.40 J/kg K at ΔH = 1.5 T (ΔH: magnetic field change) with x = 7. The maximum refrigerant capacity (RC) is 191.9 J/kg at ΔH = 1.5 T with x = 3, which is higher than that of most of Fe-based amorphous alloys so far discovered. Increasing the ΔH to 2 T, the RC values of these alloys can reach as high as 265.2 J/kg, which is comparable to those detected in crystalline Gd and Gd5Si2Ge2. Enhanced RC values observed in these alloys promise them to be good candidates for near room-temperature magnetic refrigerants.
Y. Fang, G. Peng, T. Feng, et al., Journal of Non-Crystalline Solids, 2019, 505, 211.