“…The dipolar interaction between the magnetic charges acts as a coupling field favoring parallel alignment of magnetization, inducing a surface anisotropy with easy axis along the wrinkles. The strength of surface anisotropy is estimated less than 3 × 10 3 erg/cm 3 , which is by far less than the contribution from the oblique deposition 21, 34, 35 .Figure 2Hysteresis loops with magnetic field applied parallel ( θ = 0°) and perpendicular ( θ = 90°) to wrinkles for FeCoTa films grown ( a ) with different pre-strains of 0%, 5%, 20%, 40% and ( b ) with different deposition angles of 0°, 15°, 30°, 45°.
…”
We investigated the magnetic anisotropy and the high-frequency property of flexible Fe60Co26Ta14 (FeCoTa) thin films obtained by oblique sputtering onto a wrinkled surface. The sinuously wrinkled topography is produced by growing Ta layer on a pre-strained polydimethylsiloxane (PDMS) membrane. Due to the enhanced effect of shadowing, the oblique deposition of FeCoTa layer gives rise to a shift of wrinkle peak towards the incident atomic flux. With increasing the PDMS pre-strain or increasing the oblique sputtering angle, both the uniaxial magnetic anisotropy and the ferromagnetic resonance frequency of FeCoTa films are enhanced, but the initial permeability decreases. The magnetization reversal mechanism of wrinkled FeCoTa films can be interpreted by a two-phase model composed of both coherent rotation and domain wall nucleation. With the enhancement of uniaxial magnetic anisotropy, the domain wall nucleation becomes pronounced in FeCoTa films.
“…The dipolar interaction between the magnetic charges acts as a coupling field favoring parallel alignment of magnetization, inducing a surface anisotropy with easy axis along the wrinkles. The strength of surface anisotropy is estimated less than 3 × 10 3 erg/cm 3 , which is by far less than the contribution from the oblique deposition 21, 34, 35 .Figure 2Hysteresis loops with magnetic field applied parallel ( θ = 0°) and perpendicular ( θ = 90°) to wrinkles for FeCoTa films grown ( a ) with different pre-strains of 0%, 5%, 20%, 40% and ( b ) with different deposition angles of 0°, 15°, 30°, 45°.
…”
We investigated the magnetic anisotropy and the high-frequency property of flexible Fe60Co26Ta14 (FeCoTa) thin films obtained by oblique sputtering onto a wrinkled surface. The sinuously wrinkled topography is produced by growing Ta layer on a pre-strained polydimethylsiloxane (PDMS) membrane. Due to the enhanced effect of shadowing, the oblique deposition of FeCoTa layer gives rise to a shift of wrinkle peak towards the incident atomic flux. With increasing the PDMS pre-strain or increasing the oblique sputtering angle, both the uniaxial magnetic anisotropy and the ferromagnetic resonance frequency of FeCoTa films are enhanced, but the initial permeability decreases. The magnetization reversal mechanism of wrinkled FeCoTa films can be interpreted by a two-phase model composed of both coherent rotation and domain wall nucleation. With the enhancement of uniaxial magnetic anisotropy, the domain wall nucleation becomes pronounced in FeCoTa films.
“…Such induced anisotropy has also been used to control the interlayer exchange coupling in Fe/Cr/Fe trilayers 8 or exchange biased multilayers. 9 In the literature, we basically find two methods of imprinting UMA in magnetic layers by IBS techniques: on one hand, ion erosion is applied to a substrate, usually a silicon wafer, to make ripples in its surface, i.e., to prepattern the surface onto which the magnetic film can be subsequently grown; [12][13][14][15] on the other hand, the magnetic film is first deposited on a polished substrate, later an ion beam erodes directly the film surface to induce a ripple pattern. 16,17 Other authors have pursued different strategies, for instance, Umlor has found UMA to be related to oblique deposition of a non-magnetic buffer layer; 18 similarly Yakovlev et al have made use of the intrinsic groove morphology of the CaF 2 /Si (1 0 0) interface to form a ripple pattern on the cobalt films grown atop.…”
Ion beam patterning of a nanoscale ripple surface has emerged as a versatile method of imprinting uniaxial magnetic anisotropy (UMA) on a desired in-plane direction in magnetic films. In the case of ripple patterned thick films, dipolar interactions around the top and/or bottom interfaces are generally assumed to drive this effect following Schlömann's calculations for demagnetizing fields of an ideally sinusoidal surface [E. Schlömann, J. Appl. Phys. 41, 1617 (1970)]. We have explored the validity of his predictions and the limits of ion beam sputtering to induce UMA in a ferromagnetic system where other relevant sources of magnetic anisotropy are neglected: ripple films not displaying any evidence of volume uniaxial anisotropy and where magnetocrystalline contributions average out in a fine grain polycrystal structure. To this purpose, the surface of 100 nm cobalt films grown on flat substrates has been irradiated at fixed ion energy, fixed ion fluency but different ion densities to make the ripple pattern at the top surface with wavelength Λ and selected, large amplitudes (ω) up to 20 nm so that stray dipolar fields are enhanced, while the residual film thickness t = 35–50 nm is sufficiently large to preserve the continuous morphology in most cases. The film-substrate interface has been studied with X-ray photoemission spectroscopy depth profiles and is found that there is a graded silicon-rich cobalt silicide, presumably formed during the film growth. This graded interface is of uncertain small thickness but the range of compositions clearly makes it a magnetically dead layer. On the other hand, the ripple surface rules both the magnetic coercivity and the uniaxial anisotropy as these are found to correlate with the pattern dimensions. Remarkably, the saturation fields in the hard axis of uniaxial continuous films are measured up to values as high as 0.80 kG and obey a linear dependence on the parameter ω2/Λ/t in quantitative agreement with Schlömann's prediction for a surface anisotropy entirely ruled by dipolar interaction. The limits of UMA tuning by a ripple pattern are discussed in terms of the surface local angle with respect to the mean surface and of the onset of ripple detachment.
“…Based on the comparable values of K u and K s in Table I for samples 3 and 4, we conclude that the UMA inferred from the magnetization reversal is dominated by the anisotropic surface roughness resulting from the grazing-incidence ion beam sputtering [7,12].…”
Section: B Magnetization Reversalmentioning
confidence: 66%
“…In particular, grazing-incidence ion beam sputtering has been demonstrated as a reliable tool to manipulate the magnetic anisotropy. The sputtering results in the development of nanoscale surface ripples, giving rise to an in-plane uniaxial magnetic anisotropy (UMA) with controllable orientation and strength through the sputtering conditions [5][6][7][8][9]. Bisio et al employed ion beam sputtering to achieve step-induced UMA in Fe films on flat Ag (001) substrates [10].…”
We studied surface morphology induced changes of magnetic anisotropy, magnetization reversal, and symmetry of the anisotropic magnetoresistance (AMR) in ion sputtered Ni films grown on MgO (001). Grazing-incidence ion sputtering generally develops anisotropic surface roughness of the Ni films, i.e., nanometer wide ripples parallel to the ion beam direction, giving rise to uniaxial magnetic anisotropy with the easy axis along the ion beam direction. The formed ripples act as domain wall nucleation and pinning sites during magnetization reversal, while two-jump domain wall motion dominates in the as-grown Ni films. More importantly, the azimuthal angular dependence of the AMR indicates a superposition of twofold symmetry and fourfold symmetry. By relying on grazing-incidence ion sputtering along specific crystallographic directions, we are able to tailor the relative weight of twofold and fourfold symmetry of AMR. We demonstrate that in contrast to the bulk case, the symmetry of the AMR becomes also sensitive to the surface morphology in thin films, which is in particular relevant for the design of magnetotransport based sensors.
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