Investigation of spin gapless semiconducting behaviour in quaternary CoFeMnSi Heusler alloy thin films on Si (1 0 0)

Abstract

Spin gapless semiconducting (SGS) behaviour of polycrystalline CoFeMnSi (CFMS) Heusler alloy thin films was investigated through structural, magnetic, magnetotransport and electron-transport characterization. In this study, we have tailored the structural ordering in CFMS thin films (∼60 nm) grown at different substrate temperatures (TS) in 150 °C to 550 °C range on Si(100) substrates using pulsed DC magnetron sputtering. All the grown films were polycrystalline in nature, showing an enhancement in structural ordering with TS. Among all the samples, the film grown at 550 °C showed an optimal structure with L21 ordering. The magnetic measurements revealed that saturation magnetization (Ms) of the sample decreased with the an increment in measurement temperature with a value ∼ 3.42 μB/f.u. at 5 K to 3.11 μB/f.u. at 300 K. The Curie temperature (TC) of the sample was estimated to be 778 ± 13 K. The longitudinal resistivity (ρXX) measurements clearly exhibited a negative temperature coefficient of resistivity, indicating the non-metallic behaviour of these CFMS films. The fitting of resistivity curve dig out contribution of electron–phonon scattering and defect scattering to resistivity. Fitting also suggest that holes are the majority charge carriers in optimized CFMS thin film which was further confirmed through positive slope of anomalous Hall resistivity curve. The temperature-dependent anomalous Hall effect (AHE) measurements have also been carried out to identify the different scattering mechanisms responsible for AHE. The results suggested that both the intrinsic as well as extrinsic factors contribute to the AHE of CFMS deposited film with non-zero contribution of phonon-related skew scattering. The carrier concentration (n) and mobility (μ) were found to be nearly temperature-independent, revealing typical SGS characteristics. At room temperature, the n and μ values were found to be 3.91 ± 0.04 × 1021 cm−3 and 88.83 ± 1.58 cm2/Vs, respectively. The value of anomalous Hall conductivity at 5 K is found to be 53.79 S/cm..