Hybridization of semiconducting and magnetic materials into a single heterostructure is believed to be potentially applicable to the design of functional spintronic devices. In the present work we report epitaxial stabilization of four magnetically ordered iron oxide phases (${\mathrm{Fe}}_3{\mathrm{O}}_4, \gamma -{\mathrm{Fe}}_2{\mathrm{O}}_3, \alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3$ and most exotic metastable $\varepsilon -{\mathrm{Fe}}_2{\mathrm{O}}_3$) in the form of nanometer-sized single crystalline films on GaN(0001) surface. The epitaxial growth of four distinctly different iron oxide phases is achieved by a single-target pulsed laser deposition technology on a GaN semiconductor substrate widely used for electronic device fabrication. The discussed iron oxides belong to a family of simple formula magnetic materials exhibiting a rich variety of outstanding magnetic properties including peculiar Verwey and Morin phase transitions in ${\mathrm{Fe}}_3{\mathrm{O}}_4$ and $\alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3$ and multiferroic behavior in metastable magnetically hard $\varepsilon -{\mathrm{Fe}}_2{\mathrm{O}}_3$ ferrite. The physical reasons standing behind the nucleation of a particular phase in an epitaxial growth process is discussed in the present paper deserving interest from the fundamental point of view. The practical side of the presented study is to exploit the tunable polymorphism of iron oxides in order to create the ferroic-on-semiconductor heterostructures usable in spintronic devices. By application of a wide range of experimental techniques the surface morphology, crystalline structure and electronic and magnetic properties of the single phase iron oxide epitaxial films on GaN have been studied. A comprehensive comparison has been made to the properties of the same ferrite materials in the bulk and nanostructured form reported by other research groups.

• Received 12 August 2017
• Revised 29 May 2018

DOI:https://doi.org/10.1103/PhysRevMaterials.2.073403