Evolution of the Ferromagnetism of Mn_xSi_{1 –x} (x ≈ 0.5) Films Produced by Laser Synthesis on c- and r-Cut Sapphire Substrates as the Laser Energy Density on the Target Changes

Abstract

Mn_xSi_{1 – x} (x ≈ 0.5) thin films have been produced on c- and r-cut sapphire substrates by the droplet-free pulsed laser deposition method at various laser energy densities E on the target. Their magnetic, electric, and X-ray diffraction properties as a function of E and substrate orientation have been investigated. It has been established that the high-temperature ferromagnetic phase in the films at E ≥ 6 J cm^–2 is more pronounced than that at E ≈ 4–5 J cm^–2, when the low-temperature ferromagnetic phase dominates and there is no influence of the sapphire substrate orientation. The attained Curie temperature T_C was 330 K at E ≈ 7.4 J cm^–2 for the Mn_xSi_{1 – x} films produced on c- and r-cut sapphire substrates. The magnetization of the Mn_xSi_{1 – x} films produced at E ≥ 6 J cm^–2 on c-cut sapphire is higher than that on r-cut sapphire and, conversely, lower when E ≤ 5.5 J cm^–2. A change in the ratio of the diffuse signal amplitudes in the X-ray spectra for the films grown on different substrates is also observed under these conditions. Such a correlated behavior with magnetization is explained by the existence of ε-MnSi nanocrystallites of optimal sizes, which, on the one hand, are responsible for the emergence of a diffuse signal in the X-ray spectra and, on the other hand, determine the high-temperature ferromagnetism of the films. The concentration of such nanocrystallites and the distribution of defects in the films are controlled by the type of substrate and the energy density on the target.