Alternating current susceptibility and magnetisation of nanocrystalline Co2MnSi Heusler alloy films

Abstract

The Co₂MnSi (CMS) Heusler alloy films with thickness d = 90 ÷ 110 nm were grown by DC magnetron sputtering on both nonheated and heated Si(100) and MgO(100) substrates. The films grown (annealed) at T ≥ 400°C demonstrated a nanocrystalline structure with a partially ordered B2 phase and traces of a highly ordered L2₁ phase as found from XRD measurements. The films deposited onto the nonheated substrates followed by annealing at T_ann = 300 ÷ 500°C demonstrated a gradual increase of the saturation magnetisation, M_sat, up to about 4.0 μ_B/f.u. (at 295 K) while the coercity field, H_c, of the films increased from about 10 to 12 kA/m with T_ann increasing from 400 to 500°C. Unusually low H_c values of about 0.1 and 0.3 kA/m have been indicated for the films grown in situ at 400°C on MgO and Si, respectively. A significant increase of the H_c values found for the films grown in situ at T_s = 450°C and reduced M_sat values for similar films grown at 500°C have been associated with the instability of the ordered L2₁ structure at high temperatures.