Abstract
Structural quality of LuFeO epitaxial layers grown by pulsed-laser deposition on sapphire substrates with and without platinum Pt interlayers has been investigated by in situ high-resolution X-ray diffraction (reciprocal-space mapping). The parameters of the structure such as size and misorientation of mosaic blocks have been determined as functions of the thickness of LuFeO during growth and for different thicknesses of platinum interlayers up to 40 nm. By means of fitting of the time-resolved X-ray reflectivity curves and by in situ X-ray diffraction measurement, we demonstrate that the LuFeO growth rate as well as the out-of-plane lattice parameter are almost independent from Pt interlayer thickness, while the in-plane LuFeO lattice parameter decreases. We reveal that, despite the different morphologies of the Pt interlayers with different thickness, LuFeO was growing as a continuous mosaic layer and the misorientation of the mosaic blocks decreases with increasing Pt thickness. The X-ray diffraction results combined with ex situ scanning electron microscopy and high-resolution transmission electron microscopy demonstrate that the Pt interlayer significantly improves the structure of LuFeO by reducing the misfit of the LuFeO lattice with respect to the material underneath.
Highlights
Hexagonal ferrites (h-RFeO3, R=Y, Dy-Lu) based oxide materials are an important category and promising candidates for information processing and storage [1,2]
It is obvious that the lattice parameter a is almost independent from the Pt thickness and exhibits an expected temperature dependence due to thermal expansion
The structure quality of hexagonal LuFeO3 epitaxial layers grown by pulsed-laser deposition on sapphire without and with Pt interlayers of various thicknesses has been investigated by in situ high-resolution X-ray diffraction and by scanning electron microscopy
Summary
Hexagonal ferrites (h-RFeO3 , R=Y, Dy-Lu) based oxide materials are an important category and promising candidates for information processing and storage [1,2]. The coexisting spontaneous electric and magnetic polarizations make h-RFeO3 rare-case ferroelectric ferromagnets at low temperature [3,4]. Besides the room-temperature multiferroicity and the predicted magnetoelectric effect, h-RFeO3 is a promising material for future multiferroic applications [5]. Epitaxial h-RFeO3 thin films have been deposited on various substrates including Al2 O3 (0001), yttrium-stabilized zirconium oxide (YSZ) (111), and Al2 O3 (0001) buffered with Pt (111) layers [6,7,8,9]. All the epitaxial growth occurs along the c-axis of h-RFeO3 in order to satisfy the triangular symmetry matching and to maximize the effect of interface energy with the goal to stabilize the hexagonal phase in the grown thin film. The epitaxial growth of h-RFeO3 thin films and the stabilization of Materials 2020, 13, 61; doi:10.3390/ma13010061 www.mdpi.com/journal/materials
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