Experimental and numerical understanding of localized spin wave mode behavior in broadly tunable spatially complex magnetic configurations

Abstract

Spin wave modes confined in a ferromagnetic film by the spatially inhomogeneous magnetic field generated by a scanned micromagnetic tip of a ferromagnetic resonance force microscope (FMRFM) enable microscopic imaging of the internal fields and spin dynamics in nanoscale magnetic devices. Here we report a detailed study of spin wave modes in a thin ferromagnetic film localized by magnetic field configurations frequently encountered in FMRFM experiments, including geometries in which the probe magnetic moment is both parallel and antiparallel to the applied uniform magnetic field. We demonstrate that characteristics of the localized modes, such as resonance field and confinement radius, can be broadly tuned by controlling the orientation of the applied field relative to the film plane. Micromagnetic simulations accurately reproduce our FMRFM spectra allowing quantitative understanding of the localized modes. Our results reveal a general method of generating tightly confined spin wave modes in various geometries with excellent spatial resolution that significantly facilitates the broad application of FMRFM. This paves the way to imaging of magnetic properties and spin wave dynamics in a variety of contexts for uncovering new physics of nanoscale spin excitations.

Spin-wave localization in tangentially magnetized films

“…The method can be easily generalized for different orientations of the applied field relative to the film plane, and it may prove to be useful in planning future ferromagnetic resonance imaging experiments involving spin wave localization. 24 In particular, the method is applicable to the case of normally magnetized film 21 , when the potential well is either isotropic or anisotropic.…”

Engineering the Spectrum of Dipole Field-Localized Spin-Wave Modes to Enable Spin-Torque Antidamping

“…We performed micromagnetic modeling [12,[25][26][27] Fig. 3(b), reduced by 50 G to account for the Oersted field and heating from I DC (determined by the shift of the quasi-uniform mode).…”

“…3(c). To identify the localized modes resonances, we performed micromagnetic modeling [12,[25][26][27] at θ = 70 ○ , using a value of 4πM eff = 8.7 kG, determined from the in-situ Py/Pt film (both at I DC = 0). For a Py thickness of 5 nm, the four lowest-energy localized modes are three width modes (n = 1, 2, 3) [13] and one higher-order length mode (n = 1, m = 2).…”

Nonlinear and Thermal Effects in the Absorption of Microwaves by Random Magnets

“…In the absence of rigorous theory describing static properties of the RA ferrromagnet, the studies of the dynamics present a significant challenge. Collective modes and their localization have been observed in amorphous ferromagnets with random local magnetic anisotropy [12][13][14][15][16] , inhomogeneous thin magnetic films 17 , submicron magnetic heterostructures 18 , and in films where inhomogeneous magnetic field was generated by a tip of a force microscope 19 . Complex nature of these excitations that involves longitudinal, transversal, and mixed modes has been reported.…”