Magnetic anisotropy and order structure of L1_0-FePt(001) single-crystal films grown epitaxially on (001) planes of MgO, SrTiO_3, and MgAl_2O_4 substrates

摘要

L1_0-FePt(001) single-crystal films were grown epitaxially on SrTiO_3(001), MgAl_2O_4(001), and MgO(001) substrates. Their uniaxial magnetic anisotropy K_u and the order structure were examined for the film thickness t range of 2-14 nm. All series of films show large K_u of 4 × 10~7 erg/cm~3 in the thickness range higher than 10 nm, with order parameter S of 0.8 and saturation magnetization M_s of 1120 emu/cm~3. K_u decreased gradually as t decreased. The K_u reduction was considerable when t decreased from 4nm to 2nm. No marked difference in the thickness dependence of K_u was found in any series of films, although the lattice mismatch between FePt and the substrates was markedly different. K_u reduction showed good agreement with the reduction of S for the films on MgAl_2O_4 and MgO. The K_u ～ S~2 plot showed an almost linear relation, which is in good agreement with theoretical predictions. Transmission electron microscopy images for a FePt film on MgO substrate revealed that the lattice mismatch between FePt(001) and MgO(001) was relaxed in the initial 1 or 2 layers of FePt(001) lattices, which is likely to be true also for two other series of films.