Charge transport and magnetic ordering in laser ablated Co₂FeSi thin films epitaxially grown on (100) SrTiO₃

We have successfully deposited epitaxial thin films of the Heusler alloy Co₂FeSi on (1 0 0) cut SrTiO₃ single crystal substrates by pulsed laser deposition. X-ray diffraction reveals the L2₁ cubic crystal structure for the films grown at 400 and 600 °C, with a better crystallographic quality at the higher growth temperature. The magnetic moment in saturation of the 600 °C grown film is 5.0 μ_B/fu at 5 K with the easy axis of magnetization in the (1 0 0) plane. Inplane hysteresis measurements suggest a soft magnetic state with a coercive field H_C ≈ 250 Oe at 5 K for the 600 °C film which decreases on lowering the growth temperature. The normalized magnetization of thin films follows the well-known Bloch T^3/2 law due to spin wave excitation. Electrical resistivity measurements on the films with the L2₁ crystal structure show a pronounced metallic behaviour down to the lowest temperature of measurement (≈5 K), and enhanced metallicity in the 600 °C film as indicated by its lower residual resistivity (≈0.16 μΩ cm) and higher residual resistivity ratio (RRR ≈ 1280). These results suggest that films grown at the higher temperature may be better suited for the fabrication of magnetic tunnel junctions.