Abstract
Hexagonal LuFeO3 (h-LuFeO3) is a multiferroic material that belongs to hexagonal ferrites. Magnetoelectric coupling at room temperature was theoretically predicted in this material. These properties make h-LuFeO3 very interesting for potential use in spintronics[1,2].
We investigated the real structure of the thin epitaxial layers of h-LuFeO3 by means of X-ray diffraction (reciprocal space mapping) and X-ray reflectivity. Three samples of h-LuFeO3 with (001) surface orientation were investigated. The first epitaxial layer was deposited on a sapphire substrate (001), the second layer was deposited on a platinum interlayer (111) on a sapphire substrate (001), and the third layer was deposited on an yttria-stabilized zirconia substrate (111). Despite the high mismatch between substrates and layer (up to 6.8 % for the h-LuFeO3-platinum interface), epitaxial growth was achieved in all samples. The layer thickness determined from the X-ray reflectivity was (339+-1) Å, (370+-3) Å, and (370+-1) Å, respectively.
Two symmetrical and two asymmetrical reciprocal space maps were measured for each layer (including the platinum interlayer). From the positions of the reciprocal lattice points, we determined that all layers were relaxed. All four reciprocal space maps belonging to one layer were simultaneously fitted using a model of x-ray scattering on mosaic layers[3]. This model assumes that the layer is composed of mosaic blocks in the shape of a rotational ellipsoid. These blocks are mutually slightly rotated, i.e., there is a small random tilt of the (001) planes. The layer is thus described by the following parameters: thickness, lateral and vertical average size of blocks, distribution width of block size, root mean square misorientation, vertical and lateral microstrain.
The reciprocal space maps of h-LuFeO3 layer deposited directly on the sapphire substrate show two overlapping peaks. The more intense maxima correspond to almost spherical blocks with horizontal semi axis RL = (170+-10) Å and vertical semi axis RV = (170+-10) Å with misorientation INCREMENT = (1.5+-0.1) ° and the less intense maxima correspond to blocks with RL = (100+-20) Å and RV = (170+-15) Å with misorientation INCREMENT = (1.7+-0.1) ° and slightly smaller out of plane lattice parameter.
The platinum interlayer helps to improve the crystalline quality of the h-LuFeO3 layer. The size of the mosaic blocks in the layer deposited on the platinum interlayer is RL = (125+-7) Å and RV = (115.8+-0.1) Å and misorientation of mosaic bocks is INCREMENT = (0.10+-0.02) °. The platinum interlayer is composed of a wetting layer with low mosaicity and hills with mosaic blocks of size RL= (200+-15) Å and RV = (200+-15) Å and misorientation INCREMENT = (0.25+-0.03) ° growing from this wetting layer.
In the last sample deposited on yttria-stabilized zirconia, we detected medium sized mosaic blocks RL= (183.6+-6.6) Å and RV = (182.6+-1.8) Å with medium misorientation INCREMENT = (0.31+-0.02) °. The microstrain was highest in the sample deposited directly on a sapphire substrate and lowest in the sample deposited on an yttria-stabilized zirconia substrate.