Recent Developments ofNano-particles and Thin Films of FeRh and FeRh/FePt with First Order Magnetic Phase Transition

摘要

The present paper discusses recent results of nanoparticles and thin films of FeRh, Fe(RhPt), and FeRh/ FePt bi-layers, which exhibit the first order magnetic phase transition between antiferro- and ferro-magnetic phases. For the first time, nano-particles of FeRh and FeRh/FePt are successfully fabricated by using chemical synthesis methods. An average size of such nanoparticles is about 3 nm for both as fabricated and those annealed at around 600°C for 6 h. The nano-particles after annealed are found to be of the a phase, which undergo the phase transition in a similar fashion to those of FeRh thin films and bulks. However, there is a very broad thermal hysteresis between heating and cooling, which amounts to as large as 100°C. The effect of an applied filed on phase transition during the thermal process of those nano-particles as well as thin films of FeRh and FeRhPt is studied in detail. Based on the change of a transition temperature with respect to magnetic field, an entropy change is estimated to be about 10 mJ/deg g, which is close to those of thin films and bulks. Magnetic behaviors of composite nanoparticias, of FeRh/FePt are found to exhibit an exchange bias effect, the exchange energy of which is about 0.1 to 1 erg/cm~2. A systematic study of FeRh and Fe(RhPt) thin films with various compositions is also conducted to understand the phase transition mechanism. The transition temperature of Fe(RhPt) is found to increase with Pt. No longer is the phase transition found for Pt contents beyond 15 at%.