ELECTRONIC, STRUCTURAL AND MAGNETIC PROPERTIES OF Co2FeAl THIN FILMS FOR POTENTIAL SPINTRONIC APPLICATIONS

Abstract

This paper presents an overview concerning the electronic, structural and magnetic properties of Co 2 FeAl (CFA) thin films. We first used ab initio calculations of the electronic structure in order to discuss the half-metallicity of this compound. Involving a correlated structural-magnetic analysis, we then illustrate, experimentally, the effect of the thickness as well as the annealing temperature on the magnetic and structural properties of CFA films epitaxially grown on MgO (001) single crystal substrates. The X-ray diffraction shows that in our samples having the CFA(001)[110]// MgO (001)[100] epitaxial relation, the chemical order is enhanced as the thickness and the annealing temperature (T a ) are increased. Ferromagnetic resonance measurements reveal further dynamic magnetic properties. The gyromagnetic factor, estimated at 29.2 GHz/T, is both thickness and annealing temperature independent. The in-plane anisotropy results from the superposition between a dominant fourfold symmetry term, as expected for cubic crystal symmetry of the alloy, and a small uniaxial term. The fourfold anisotropy decreases with increasing thickness and annealing temperature. The exchange stiffness constant is thickness independent but increases with T a . In addition, the effective magnetization varies linearly with T a and with the inverse CFA thickness. This is due to the presence of perpendicular uniaxial anisotropy, estimated around -1.8 erg/cm2 at T a = 600°C and 1.05 erg/cm2 at T a = 265°C, respectively. Frequency and angular dependences of the FMR linewidth show two magnon scattering and mosaicity contributions which depend on the CFA thickness and T a . A Gilbert damping coefficient as low as 0.0011 is found for samples annealed at 600°C. Finally, we illustrate that these films can be used as ferromagnetic electrodes in sputtered epitaxial magnetic tunnel junctions (MTJ) based on MgO (001) tunnel barriers. These MTJs show an improvable TMR ratio around 95% at room temperature.