Abstract
The metastable ε-Fe2O3 is known to be the most intriguing ferrimagnetic and multiferroic iron oxide phase exhibiting a bunch of exciting physical properties both below and above room temperature. The present paper unveils the structural and magnetic peculiarities of a few nm thick interface layer discovered in these films by a number of techniques. The polarized neutron reflectometry data suggests that the interface layer resembles GaFeO3 in composition and density and is magnetically softer than the rest of the ε-Fe2O3 film. While the in-depth density variation is in agreement with the transmission electron microscopy measurements, the layer-resolved magnetization profiles are qualitatively consistent with the unusual wasp-waist magnetization curves observed by superconducting quantum interference device magnetometry. Interestingly a noticeable Ga diffusion into the ε-Fe2O3 films has been detected by secondary ion mass spectroscopy providing a clue to the mechanisms guiding the nucleation of exotic metastable epsilon ferrite phase on GaN at high growth temperature and influencing the interfacial properties of the studied films.
Highlights
The combination of magnetic and semiconductor materials within a single heterostructure provides vast opportunities for designing novel functional spintronic devices[1,2,3]
In contrast to our previous report[15] which focused either on the near surface region or on the bulk-integrated properties (X-ray diffraction, vibrating sample magnetometry), the present paper involves a depth resolved analysis of the ε-Fe2O3/GaN films performed by polarized neutron reflectometry (PNR), transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS)
All PNR datasets were fitted simultaneously with the same structural parameters and varying magnetizations of the main and interface layers corresponding to different temperature and field conditions and resolution functions corresponding to the D17 and SHARAKU instruments
Summary
For quantitative discussions of the structure and magnetic properties of the studied sample the PNR data were fitted using the Parratt algorithm in GenX software package[35]. For neutron reflectometry the buffer GaN layer with thickness of 3 μm is considered as the bulk medium. Reflectivity data was fitted assuming the model consisted of GaN substrate, transition layer (interface) and ε-Fe2O3 layer. These parameters are summarized in the nuclear scattering length density (SLD) and magnetic SLD profiles (ρn(z) and ρm(z), respectively) shown in Fig. 3b and c
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