Volume effects on microstructures and magnetic properties of MnGa thin films during order-disorder transformation

Abstract

In this study, L10 MnGa thin films were grown on an amorphous glass substrate, and the relationship between the volume effect and the magnetic properties of thin films as a function of the film thickness was investigated. An amorphous thin film and weak magnetic properties were observed at the thickness of 10 nm. With the increase in thickness, the magnetization (M10 kOe) and coercivity (Hc⊥) also increased. The maximum M10 kOe and Hc⊥ values were 106.3 ± 5.7 emu/cm3 and 8.54 kOe in a 200 nm-thick sample, respectively. X-ray diffraction indicated that the order-disorder transformation occurred when the thickness was greater than 25 nm. Plan-view transition electron microscopy (TEM) images indicated the emergence of larger grains and blurred grain boundaries when the thickness was increased beyond 25 nm, while cross-sectional TEM images suggested that the appearance of nuclei promote the growth of columnar MnGa grain structures. Energy dispersion spectroscopy analysis indicated that the composition of MnGa was Mn-rich (or Ga-poor) in the nuclei at the initial growth state and then gradually changed to Mn50Ga50 as the thickness increased. In addition, the effects of the base pressure of the chamber on the phase and magnetic properties of the MnGa films were also investigated.