FMR study of thin films of Co₂Cr_0.6Fe_0.4Al and Co₂MnSi Heusler alloys

Abstract

The method of ferromagnetic resonance (FMR) was used to study magnetic properties of thin films of half-metallic ferromagnetic Heusler alloys Co₂Cr_0.6Fe_0.4Al and Co₂MnSi depending on the film thickness and the presence or absence of a vanadium buffer layer. It is shown that the FMR method is a highly efficient technique for studying nanoscale magnetic properties of thin films, especially for the investigation of their magnetic inhomogeneities and anisotropy. Samples of Co₂Cr_0.6Fe_0.4Al and Co₂MnSi were prepared by magnetron-sputtering deposition on substrates of single-crystal silicon dioxide (SiO₂) with an orientation (100). It has been shown that the magnetic properties of thin Co₂Cr_0.6Fe_0.4Al films strongly depend on both the film thickness (25 or 100 nm) and the presence of an intermediate vanadium layer (50 nm). Well-resolved spin-wave modes were observed in the sample 100 nm thick without a vanadium buffer layer, which made it possible to determine the parameter of spin stiffness D for this ferromagnet. Two series of thin films of Co₂MnSi have also been studied, which were prepared on a buffer layer of vanadium (42 nm thick): (1) with various thicknesses (4–100 nm) and a fixed annealing temperature (450°C) and (2) with a fixed thickness (80 nm) and various annealing temperatures (425–550°C). It has been shown that in the series of Co₂MnSi films with a variable thickness (4–100 nm) the greatest value of magnetization is reached for a film with a thickness of 61 nm. The investigations of the other series of films, which were annealed at various temperatures, show that to achieve both a greater magnetization and a better structural homogeneity, annealing at temperatures T ≥ 450°C is required. In addition, low-intensity spin-waves were observed in some samples with thicknesses of 100 and 61 nm, which made it possible to estimate the spin-stiffness parameter D for the Co₂MnSi Heusler alloy as well.