Preparation of helimagnetic substrates for thin-film epitaxy of magnet-superconductor heterostructures

Abstract We have prepared substrates for thin-film deposition from Czochralski-grown MnSi and Fe <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi/> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> Co x Si single crystals. The crystals have been investigated using x-ray diffraction and oriented according to Laue patterns. From these crystals we have prepared substrates for thin film deposition by mechanical polishing and chemical etching procedures. The surface roughness of the prepared substrates has been investigated in terms of atomic force microscopy and is in the order of 1 nm. Thermal annealing followed by Ar-sputtering improves the quality of the surface which is evidenced by reflection high-energy electron diffraction analysis. Subsequently, Nb thin films with varying thickness ranging from 10 to 40 nm have been deposited using molecular-beam epitaxy. Transmission electron microscopy in combination with energy-dispersive x-ray spectroscopy shows a homogenous film with 5 nm oxide layers at the interface between the substrate and the film as well as at the film surface.