Curie temperatures of annealed FePt nanoparticle systems

Abstract

The chemically synthesized Fex Pt100-x nanoparticles with controlled compositions were annealed to transfer the disordered face-centered-cubic structure to the ordered structure. It was found that the L 10 FePt structure can be formed in the wide compositional region of x=40-68, and lower or higher Fe content leads to formation of the L 12 Fe Pt3 or Fe3 Pt phase, respectively. The Ńel temperature of L 12 Fe Pt3 phase and Curie temperatures (TC) of L 10 FePt and L 12 Fe3 Pt phases are all strongly composition dependent. The room-temperature saturation magnetization has an abnormal dependence on x which is caused by the low TC of Fe3 Pt phase with x=75-79. The big difference in TC between the heating and cooling thermomagnetic curves of the Fe-Pt alloys with x=79-90 can be attributed to the difference of αγ phase transition temperature during heating and cooling. On the other hand, TC of the L 10 FePt nanoparticles was found to be strongly size dependent. © 2007 American Institute of Physics.