Calorimetry of ferromagnetic ↔ paramagnetic phase transitions in iron, cobalt, nickel

Abstract

There are some special features in calorimetry signal introduced by the ferromagnetic ↔ paramagnetic phase transitions in magnetic materials. The purpose of this study was to investigate, by means of high-resolution differential scanning calorimetry, the effects of heat flux change during direct and reverse second-order phase transformations of the type ferromagnetic ↔ paramagnetic in some high-purity metals possessing natural ferromagnetism: iron, cobalt, and nickel. The literature review indicates that so far there has been no research describing such phase transitions with the help of differential scanning calorimetry. Our study detected anomalies in the dependences of heat flux intensity on temperature. There was noted a shift to the region of higher temperatures during heating in the range of thermocycling rates of 5-10-20-40 K/min. A shift to the region of lower temperatures during cooling in the same range of thermocycling rates was observed in the area of registration of second-order phase transition. The possibility of using calorimetric measurements for estimating the Curie temperature at ferromagnetic ↔ paramagnetic transitions in the metals is shown. The authors highlight that, when conducting high-resolution calorimetric measurements, it is essential to take into consideration in the total heat flux balance the possible contribution from the effects associated with second-order phase transitions, including, in particular, ferromagnetic ↔ paramagnetic transitions.