Co2FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

Abstract

10 nm and 50 nm Co2FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to the relation CFA (001)[110]//MgO(001)[100] epitaxial relation), respectively for CFA films grown on a Si and on a MgO substrate. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (Ta) while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and of a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing Ta while the uniaxial anisotropy field is nearly unaffected by Ta within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with Ta. Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1 × 10 −3 and 1.3 × 10 −3 for films of 50 nm thickness annealed at 615°C grown on MgO and on Si, respectively).

Thermal effect on structure and magnetic properties in CoFeAlSi alloy films

“…3b. For the as-deposited film the fitted uniaxial anisotropy K μ is 2.7 × 10 4 erg/cm 3 , which is in the same order of magnitude as that reported in Co 2 FeAl alloy films sputtered on MgO [17]. The uniaxial anisotropy increases with the annealing temperature reaching a peak value of 5 × 10 4 erg/cm 3 at 400°C and then falls down to zero at 600°C.…”

“…This trend can be explained by relating the grown grain size of the crystallites to the magnetic exchange length [20]. The saturation magnetization M s increases with the annealing temperature, which can be attributed to the improved atomic ordering and crystalline quality [17]. Further annealing above 600°C leads to a decrease in Ms.…”

“…However, changes in surface roughness, band gap, saturation magnetization, and Gilbert damping constant etc. are found in the Heusler alloys after thermal treatment [15][16][17][18]. Interdiffusion or phase separation may happen during the annealing at high temperatures, which reduces TMR ratio of MTJs [18,19].…”

Magnetic, structural and transport properties across the Heusler alloy (Co2FeAl)/n-Si interfacial structure

“…Block et al [8] have also presented study on Co 2 Cr 0.6-Fe 0.4 Al and reported -30 % MR at RT. Belmeguenai et al [9] studied the effect of annealing temperature on Co 2 FeAl Heusler alloy thin films on Si and MgO substrates. Yadav and Chaudhary [10] investigated the structural and dynamical magnetic response of Co-sputtered Co 2 FeAl Heusler alloy thin films grown at different temperature.…”

Ni_2FeSi Heusler Glass Coated Microwires

“…Thus, the Heusler alloys prepared by arc melting or grown as thin films are required to initiate the necessary structural ordering through performing long time and high temperature annealing treatments [3]. To avoid this disadvantageous step, alternative rapid quenching production of the Heusler alloys has been recently carried out [4].…”