Magnetism and structure of ε-Fe2O3 films grown on GaN and MgO buffer layer
Ioffe Institute, Sergei Suturin
Paul Scherrer Institute, Victor Ukleev
1. Introduction
Hybridization of semiconducting and magnetic materials into a single heterostructure isbelieved to provide opportunities for designing novel functional spintronic devices. The iron oxides
form a big family of magnetic materials exhibiting a rich variety of outstanding physical properties.
The metastable ε-Fe2O3 is known to be the most intriguing ferrimagnetic and multiferroic ironoxide phase exhibiting a bunch of exciting physical properties both below and above room
temperature [1]. The feasibility to grow the exotic ε-Fe2O3 phase along with three other iron oxide
phases (Fe3O4, α-Fe2O3 and γ-Fe2O3) has been demonstrated [2]. Placing the iron oxide film having
controllable spontaneous magnetization / polarization next to the active zone of the GaN-based
semiconductor devices is expected to add magnetic related functionality to these devices and topresent interest from the point of view of potential use in novel designs for (opto-) electronic andspintronic applications.
1. Gich, M. et al., Advanced Materials, 26, 4645–4652 (2014).
2. Suturin, S. et al., arXiv 1712.05632 [cond-mat.mtrl-sci] 1712.05632 (2017).
3. Ukleev, V., et al., Scientific reports, 8,1, 8741 (2018).

2. Experiment
Polarized neutron reflectometry (PNR) experiment has been performed at SHARAKU
time-of-flight instrument. The temperature and magnetic field at the instrument were controlled by
4T horizontal field cryomagnet. Polarization of the direct beam was measured by analyzer for eachvalue of magnetic field used in the experiment. The amplitudes of PNR curves were corrected forpolarization efficiency.
4.

Results
PNR experiment has been performed for layer-resolved measurement of magnetization

distribution inside the heterostructure. PNR curves R(Qz) measured at temperatures T = 5 K areshown in Fig 1. Note, that all the curves measured at high field B = 3 T are shifted along verticalaxis for clarity. The splitting of R+(Qz) and R-(Qz) is proportional to the net magnetization of the film
along the field direction. PNR data was fitted assuming the model consisted of GaN, transitionlayer (interface) and ε-Fe2O3 layer, consequently. The initial model contained the table values ofscattering lengths and densities and nominal thickness of iron oxide layer, then the densities andthicknesses of Fe2O3 and interface layer were allowed to vary freely in the fitting routine. Iron oxide
density is consistent compared to the calculated value. The minimum of the fitting algorithm
corresponds to the model containing an interface layer with thickness of 80-90 Å and roughness 30
Å between iron oxide and GaN buffer. In contrast to our previous result [3], the nuclear SLD of thetransition layer is much lower than one of Fe2O3, GaN and GaFeO3 (Fig. 2). Moreover, the interface
layer becomes non-magnetic (right panel in Fig. 2 corresponds to the magnetic SLD).
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Figure 1 Low-temperature PNR curves measured from ε-Fe2O3/GaN samples grown at various
conditions.

Figure 2 Nuclear and magnetic SLD profiles corresponding to the fitted PNR models.

4. Conclusion
The polarized neutron reflectometry data suggests that the composition and density ofinterface layer resembles non-magnetic Ga2O and soft-magnetic GaFeO3 depending on the growth
conditions. 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 SQUID [3]. A noticeable Ga
diffusion into the ε-Fe2O3 films has been detected by providing a clue to the mechanisms guiding
the nucleation of exotic metastable epsilon ferrite phase on GaN at high growth temperature andinfluencing the interfacial properties of the studied films [3]. The diffusion of Ga ions can be
successfully blocked by growth of Ga2O interlayer between GaN and iron oxide film.
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