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.

Heusler alloys for spintronic devices: review on recent development and future perspectives

“…Such technique relies on the use of different atomic scattering factors (f Co and f Fe ) of Co and Fe for Co Kα source. Hence, superlattice diffraction intensities for Co Kα can reflect the D0 3 disorder [172]. A physical model proposed by Niculescu et al was used so that the disorder parameters can be expressed in terms of α, β and γ.…”

Effective 90-degree magnetization rotation in Co2FeAl thin film/piezoelectric system probed by microstripline ferromagnetic resonance

“…A 5 nm thick Ta cap layer was deposited on the top of the CFA film in order to protect it from oxidation. CFA was chosen because of its non-negligible magnetostriction coefficient at saturation even in a polycrystalline film with no preferred orientation (λ ≈ 14×10 −6 ) [16,17] which will produce strong indirect magnetoelectric field and also because it is a serious candidate for spintronic applications [18][19][20]. Moreover, we have shown that Kapton substrate does not affect the whole system magnetoelectric behavior because of its high compliance [9,11].…”