Glancing Angle Deposition-Induced Asymmetric Growth and Magnetic Anisotropy in Co2FeAl/C60 Thin Films

Abstract

Owing to rapid interest in the magnetic properties of metal–organic bilayers for use in organic spintronics, a series of Heusler alloy Co₂FeAl (CFA) films were grown using glancing angle deposition (GLAD) on organic layers (fullerene-C₆₀) to investigate the evolution of magnetism and its correlation with morphological development at the interfaces with different thicknesses of CFA films. The magneto-optic Kerr effect, grazing incidence small-angle X-ray scattering (GISAXS), and X-ray diffraction (XRD) techniques are employed for the magnetic, morphological, and structural characterizations. The amorphous growth of CFA is validated through XRD measurements, while GISAXS uncovers the asymmetric morphology arising due to the columnar growth of CFA. Hysteresis loop measurement at low temperatures suggests the superparamagnetic behavior of CFA at low thickness due to the formation of small CFA clusters inside the C₆₀ layer. At higher film thickness, the formation of a diffused CFA layer prevailed over the magnetization reversal by the coherent rotation of the magnetic moments. In the top CFA layer, magnetization reversal mechanism is facilitated by the combined effect of domain wall nucleation and coherent rotation of moments. Compared to the literature, where the oblique angle deposited magnetic films on inorganic materials exhibit magnetic anisotropy and coercivity variation in the film plane as per the standard Stoner–Wohlfarth model, the observed anomaly in the magnetic anisotropy and angular-dependent coercivity variation in the present case are attributed to the coupling between the magnetization reversal mechanism in the bulk and the diffused CFA layer. Thus, a deep insight into the magnetic anisotropy and its tunability in the glancing angle deposited films is essential to achieve the desired functionality of diffusion-controlled organic spin valve structures.