| Abstract Scope |
At a first-order phase transition point TC, equivalence of free energies in low- and high-temperature phases gives the following relation between internal energy U and entropy S ; U high – U low = TC ( S high – S low ). Namely, latent heat is governed by the energy difference ΔU between two states. In the itinerant-electron systems, like La(Fe,Si)13 or MnFe(Si,P), ΔU is enhanced by electron-correlations, while characteristic spin-fluctuations bring down TC around room temperature, resulting in high potential for magnetocaloic effect. In addition, when an energy barrier of the transition is attributed to electronic structures, its height is lower than that formed by atomic origin like a lattice deformation, resulting in smaller hysteresis. In the magnetics history, the magnetocaloric application is the first demonstration which utilizes the itinerant-electron spin fluctuations. The electronic tuning based on materials science is therefore most essential strategy in application of these materials. |