Synthesis, structure and magnetic properties of L10 alloy (FePt)100−x Zn x nanoparticles

Abstract

In the present work, alloy (FePt)100−xZnx nanoparticles have been successfully synthesized by simple wet chemical method with the aid of Pt(acac)2, Fe(acac)3 and Zn(acac)2 as the starting reagents. Oleic acid and oleylamine was used as a surfactant agent. The addition of zinc promoted the face-centered cubic to tetragonal phase transition. Reduction in temperature required for this transition compared with FePt nanoparticles with no additives. This reduction in ordering temperature significantly reduces FePt particle coalescence and enhancing chemical ordering, so magnetic measurements show high coercivity up to 6 kOe of the (FePt)82Zn18 nanoparticles with average size <10 nm after annealing at 500 °C for 60 min. The coercivity increases with the content of zinc up to 18 %, and above this percent, the coercivity starts to decrease. In order to calculate magnetic properties for Zn in FePt: Zn structure, we used density functional theory and GGA approximation. The energy of FePt: Zn structure in which Zn atom replaces Fe ones is lower than other possible structures, so forming of this system is more probable. Calculations show than Zn atoms do not have a significant magnetic momentum when replacing Fe atoms. Curie temperature variation as a function of added Zn atoms is derived. Added Zn atoms replace Fe atoms and previous Fe site is occupied with Zn with approximately zero magnetic momentum. Since these sites are randomly occupied, we have random exchange interactions in the system which can be modeled like spin glass system. Zn atoms have a zero magnetic momentum when replacing Fe atoms, so total magnetic momentum and Curie temperature of FePt: Zn structure decrease with increasing Zn percentage.