The magnetic properties of strained and relaxed Fe3-xMgxO4 ferrite films on MgO(001) and SrTiO3(001) by molecular beam epitaxy.

The present study grows a series of Fe_3-xMg_xO₄ (0≤x≤1.5) films and systematically measure both structure and magnetization of these films. These films are grown on MgO and SrTiO₃ (STO), which have small (∼-0.3%) and large (∼7.5%) lattice mismatch in order to have either strained or relaxed films, by plasma-oxygen-assisted molecular beam epitaxy, respectively. X-ray diffraction (XRD) is carried out to analyze the crystalline structure. Saturation magnetization (M_s) of pure Fe₃O₄ (x=0) on both substrates is ∼500 emu/cm³, which is consistent with the bulk value. However, M_s has a fast decrease with increasing x for the films grown on MgO(001), from 340 to ∼100 emu/cm³ in the region of 0.3<x<1.35, and stays at ∼100 emu/cm³ for x>1.35. On the other hand, M_s remains unchanged with x increasing from 0.3 to 1 for the film grown on STO. With x>1, M_s drops abruptly to ∼100 emu/cm³, which is comparable to M_s of the film grown on MgO. The discrepancy in M_s of Fe_3-xMg_xO₄ film grown on MgO and STO may imply that the cation distribution of these films may be fundamentally different. Possible cation distribution and the substrate strain effect will be discussed. [ABSTRACT FROM AUTHOR]