Growth of Co2FeAl Heusler alloy thin films on Si(100) having very small Gilbert damping by Ion beam sputtering

Abstract

The influence of growth temperature Ts (300–773 K) on the structural phase ordering, static and dynamic magnetization behaviour has been investigated in ion beam sputtered full Heusler alloy Co2FeAl (CFA) thin films on industrially important Si(100) substrate. The B2 type magnetic ordering is established in these films based on the clear observation of the (200) diffraction peak. These ion beam sputtered CFA films possess very small surface roughness of the order of subatomic dimensions (<3 Å) as determined from the fitting of XRR spectra and also by AFM imaging. This is supported by the occurrence of distinct Kiessig fringes spanning over the whole scanning range (~4°) in the x-ray reflectivity (XRR) spectra. The Gilbert damping constant α and effective magnetization 4πMeff are found to vary from 0.0053 ± 0.0002 to 0.0015 ± 0.0001 and 13.45 ± 00.03 kG to 14.03 ± 0.04 kG, respectively. These Co2FeAl films possess saturation magnetization ranging from 4.82 ± 0.09 to 5.22 ± 0.10 μB/f.u. consistent with the bulk L21-type ordering. A record low α-value of 0.0015 is obtained for Co2FeAl films deposited on Si substrate at Ts ~ 573 K.

Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Film Heterostructures

“…The latter M-H loop exhibits lower saturation field compared to the former suggesting that the CFA film possesses perpendicular magnetic anisotropy. The saturation magnetization is found to be 838 ± 40 kA/m which is smaller than the value of 1000 kA/m reported for the bulk samples 34 which is due to the finite size effect in ultrathin films. The perpendicular uniaxial magnetic anisotropy energy, evaluated from the difference in the measured values of saturation fields, was found to be 2.90(±0.05) × 10 5 J/m 3 .…”

“…1(a) in ref. 34 ].

Figure 1Slow scan GAXRD pattern of ( a ) Si(100)/Ta(10 nm)/CFA(1.8 nm)/MgO(2 nm) heterostructure (peaks marked with * correspond to the Si substrate). Normalized SIMS sputter depth profiles recorded on ( b ) Si/Ta(10)/CFA(1.8)/MgO(2) and ( c ) Si/Ta(10)/CFA(1.0)/MgO(2) hetero-structures.

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“…The studies clearly suggest that the topological nature of the skyrmions makes them very exciting for applications in spintronic devices, primarily due to the giant reduction in the threshold current density by five to six orders of magnitude compared to the current density reported in currently employed FMs for driving the domain walls 31,32 . Even at low current density, the skyrmions are expected to move with high speed especially in materials with low Gilbert damping 33 such as Heusler alloys which are established for low Gilbert damping 34 . Fert’s group has theoretically predicted the formation of skyrmions by means of micromagnetic simulations in confined media 3 .…”

“…To the best of our knowledge, the existence of skyrmions in high spin-polarized materials, i . e ., full Heusler alloys such as Co 2 FeAl (CFA) which possess low damping constant 34 , high Curie temperature 20 , large spin polarization 43 and tunable spin-dynamics properties 44,45 is yet to be reported. Despite the rapidly increasing number of experimental studies for gaining further insight into understanding the stabilization of skyrmions in ultrathin films, the robust formation of skyrmions at room temperature in large continuous thin films continues to be an exciting area.…”

Quantum damping of skyrmion crystal eigenmodes due to spontaneous quasiparticle decay

“…For the magnetically active C mode, with energy ε C ∼ JS(D/J ) 2 , the relative importance of quantum to classical damping reads 2 . Since ultralow α ∼ 10 −4 -10 −3 is possible in both metals [128][129][130][131][132][133][134][135][136][137] and insulators [138], quantum damping may dominate over classical damping (R C > 1), e.g., R C ≈ 3.6 in Cu 2 OSeO 3 with α = 10 −4 [138], a prediction that may be experimentally tested in the recently discovered low-temperature SkX [139].…”