Marius Kamp (Kiel / DE), Dennis Seidler (Kiel / DE), Jeffrey McCord (Kiel / DE), Lorenz Kienle (Kiel / DE), Redwanul M. Islam (Kiel / DE)
Abstract text (incl. figure legends and references)
Introduction
Due to its ferromagnetic properties, γ´´-Fe4N can be applied in spintronic applications, while the microstructure and crystal orientation influence the switching behavior 1. The focus of this contribution is set on the deposition of epitaxial thin films on single-crystal substrates like MgO by reactive magnetron sputtering. In contrast to other physical or chemical vapor deposition methods (molecular beam epitaxy, electron beam physical vapor deposition, atomic layer deposition) 2, phase-pure epitaxial vapor deposition by magnetron sputtering is more challenging, however, this method is much more widely used and allows easier scaling of the production process.
Objectives
The analysis of the γ´´-Fe4N thin films allows to elucidate the growth conditions of epitaxial thin films. In particular, conclusions may be drawn about the nucleation phase of thin film growth by reactive DC magnetron sputter deposition. An interface layer, between the substrate and the film, might originate from a tetragonal distortion of the cubic γ´´-Fe4N crystal structure or a phase transformation with local variations in chemical composition.
Materials & methods
The microstructure, chemical composition, and the magnetic properties of γ´´-Fe4N thin films are investigated by XRD, vibrating sample magnetometry, magneto-optical microscopy, and spectrum imaging including high resolution scanning transmission electron microscopy, energy dispersive X-ray, and electron energy-loss spectroscopy. To verify the chemical composition of the thin (5 nm) interface layer, EDX and EELS spectroscopy has to be to be applied.
Results
The epitaxially grown γ´´-Fe4N thin films indicate the formation of an interface layer between the substrate and the thin film with a tetragonal distortion of the cubic crystal structure and a lower nitrogen concentration. This observation indicates the formation of a metastable tetragonal phase such as α´´-Fe8N 3. Next to the inhomogeneous interface layer, the epitaxial γ´´-Fe4N thin film is rotated against the substrate by 2.4° along the growth direction, which agrees with the observed tilting of cubic magnetocrystalline anisotropy.
Conclusion
The analysis of the chemical composition of the interfacial layer of γ´´-Fe4N thin films provide insight into the growth conditions of epitaxial thin films. In particular, the nucleation phase of thin film growth by reactive DC magnetron sputter deposition is investigated. The intrinsic interface layer shows a tetragonal distortion of the cubic γ´´-Fe4N crystal structure and a phase transformation with local variations in chemical composition.
1 Seema, P. Gupta, D. Kumar, V. R. Reddy and M. Gupta, Applied Surface Science Advances, 2021, 5, 100088.
2 N. I. M. Nadzri, D. M. S. Ibrahim and S. Sompon, IOP Conf. Ser.: Mater. Sci. Eng., 2019, 701, 012047.
3 I. Dirba, P. Komissinskiy, O. Gutfleisch and L. Alff, Journal of Applied Physics, 2015, 117, 173911.