Critical thickness for stripe domain formation in FePt thin films: Dependence on residual stress

Abstract

Magnetically soft FePt thin films of varying thickness (20 nm ≤ d ≤ 100 nm) were sputter-deposited at different Ar pressures in order to systematically modify the residual stress and hence the magnetic anisotropy. The magnetic domain structure of FePt thin films showed a transition from planar to nearly parallel stripes above a critical thickness, dcr, which was found to depend on an anisotropy contribution perpendicular to the film plane, originated essentially in magnetoelastic effects. A careful structural characterization was made in order to obtain the strain and the stress induced magnetic anisotropy in the samples. Vibrating sample magnetometry and magnetic force microscopy were used to investigate the changes occurring in the magnetic domain structure and the critical thickness of each set of films. Joining together structural and magnetic results, we have been able to construct a phase diagram that divided regions of different domain structures, either by changing the film thickness or the perpendicular magnetic anisotropy. The experimental results could be satisfactorily explained by using a model developed by Murayama. The observed dependence of the magnetic properties of soft FePt thin films on the fabrication conditions opens the possibility to tune the magnetic domain configuration from planar to stripe-like domains by changing the argon sputtering pressure used during film deposition.

Weak Stripe Angle Determination by Quantitative x-ray Magnetic Microscopy

“…A large variety of materials are shown to develop WSs and the conclusions of our study could be extended to those materials such as Co-Gd [5], Fe-Pt [6], (Fe, Co)AlON [7], Fe-Zr-N [8], Fe 80 Ga 20 [9], (Fe, Si)B [10,11], and Fe-Ni [12][13][14]. Depending on the material's properties, film composition [12][13][14], and deposition conditions [2,3,15,16], the critical thickness leading to WS appearance varies from 20 nm for epitaxial Co [17] and 100 nm for (Fe, Ta)C [18] to 355 nm for Ni 82 Fe 18 [14]. WSs are also observed in amorphous (Co, Fe)B films [16,19,20].…”

“…Competition with the thin-film shape anisotropy, equal to (μ 0 /2)M 2 S (M S is the material magnetization at saturation), induces in-plane magnetization when a film is typically several nanometers thick. However, above a critical thickness [1][2][3], the magnetization starts to deviate from the film plane by stabilizing magnetic stripes, a wavy structure in which a small component of perpendicular magnetization develops (see Fig. 1).…”

Magnetoelectric control of spin currents

“…9 FePt alloy also displays potentially interesting magnetostrictive properties. [9][10][11] The A1 phase, in contrast to the ordered L1 0 phase, has a well defined magnetic resonance absorption line, 11 making it ideal to be used as a test-bed magnetostrictive film in spin pumping investigations. In previously published results 12 we have also analyzed the microwave properties of a magnetoelectric (ME) lead magnesium niobate-lead titanate (PMNT)/FePt heterostructure under E-and magnetic H-fields tuning control.…”

Magnetoelectric tuning of the inverse spin-Hall effect

“…5 As a consequence the A1 phase presents a dominant easy plane shape anisotropy and in contrast to the ordered L10 phase, has a well defined magnetic resonance absorption line. Additionally, FePt alloy displays potentially interesting magnetostrictive properties, 6 making it ideal to be used as a test-bed magnetostrictive film in spin pumping investigations. Spin pumping through the metallic interface was induced by driving the FePt layer to the ferromagnetic resonance (FMR) condition.…”

“…In this investigation, the resonance field position obtained in the vicinity of E=0 is coincident with values obtained in previous works on samples of FePt grown on 100 oriented Si wafers, where a resonance field between 900-1100 Oe was measured. 6,11 In order to analyze V ISHE as a function of the E-field, it is necessary to explore the effect of the magnetoelastic anisotropy fields on the spin current pumped during the FMR experiment. The magnetization precessing in the ferromagnetic film loses angular momentum generating an interfacial (FePt/Pt) spin current that propagates diffusively across the thickness of the Pt film and vanishes exponentially at the opposite interface (Pt/air).…”