Epitaxial film growth and magnetic properties of Co_2FeSi

TL;DR

This study reports on the epitaxial growth and magnetic properties of Co_2FeSi thin films, revealing orientation-dependent growth, magnetic anisotropy, and reduced surface spin polarization, with implications for spintronic applications.

Contribution

It demonstrates controlled epitaxial growth of Co_2FeSi films on different substrates and characterizes their magnetic and electronic properties, including surface spin polarization.

Findings

Epitaxial growth achieved on MgO and Al_2O_3 substrates with different orientations.

Magnetic measurements show saturation magnetization of 5.0 μ_B/fu at 0 K.

Surface spin polarization is significantly reduced compared to bulk expectations.

Abstract

We have grown thin films of the Heusler compound Co_2FeSi by RF magnetron sputtering. On (100)-oriented MgO substrates we find fully epitaxial (100)-oriented and L2_1 ordered growth. On Al_2O_3 (11-20) substrates, the film growth is (110)-oriented, and several in-plane epitaxial domains are observed. The temperature dependence of the electrical resistivity shows a power law with an exponent of 7/2 at low temperatures. Investigation of the bulk magnetic properties reveals an extrapolated saturation magnetization of 5.0 mu_B/fu at 0 K. The films on Al_2O_3 show an in-plane uniaxial anisotropy, while the epitaxial films are magnetically isotropic in the plane. Measurements of the X-ray magnetic circular dichroism of the films allowed us to determine element specific magnetic moments. Finally we have measured the spin polarization at the surface region by spin-resolved near-threshold photoemission and found it strongly reduced in contrast to the expected bulk value of 100%. Possible reasons for the reduced magnetization are discussed.