Thermal evolution of magnetic anisotropy of Fe nanoparticles

Abstract Magnetic properties and the surface morphology of Fe deposited on Pt/Al 2 O 3 (1 1 2¯ 0) were in situ studied by magneto-optical Kerr effect (MOKE) and scanning tunneling microscopy (STM), respectively. The surface morphology exhibits that the as-deposited Fe nanoparticels have a narrow sized distribution of diameter around 4.2 nm, revealing the major out-of-plane magnetization. After annealing to 200 °C, this out-of-plane magnetization is strongly enhanced while the sized distribution of nanoparticles is almost unchanged. For the further annealing procedure to 400 °C, the nanoparticles begin to coalesce into larger ones. Meanwhile, the magnetization reorients from out-of-plane to in-plane direction. Therefore, clear evidence of concurrence for nanoparticles coalescence and magnetization reorientation show that the surface evolution plays an important role on the magnetic transition.