Collective magnetization dynamics in nanoarrays of thin FePd disks

Abstract

We report on the magnetization dynamics of a square array of mesoscopic discs, fabricated from an iron palladium alloy film. The dynamics properties were explored using ferromagnetic resonance measurements and micromagnetic simulations. The obtained spectra exhibit features resulting from the interactions between the discs, with a clear dependence on both temperature and the direction of the externally applied field. We demonstrate a qualitative agreement between the measured and calculated spectra. Furthermore, we calculated the mode profiles of the standing spin waves excited during a time-dependent magnetic field excitations. The resulting maps confirm that the features appearing in the ferromagnetic resonance absorption spectra originate from the temperature and directional dependent inter-disc interactions. arXiv:1902.00403v1 [cond-mat.mes-hall]

Emergent anisotropy in magnetic metamaterials

“…We provide experimental evidences of a configurational dependence in the energy of mesospins forming a square lattice. An emerging anisotropy is obtained, in line with previous findings [23,[26][27][28][29]. We demonstrate the effects of the anisotropy in the interaction energy by determining the directional dependence of the thermally induced transition from dressed collinear states to vortex states of the elements.…”

“…Disks, mimicking the actual mesospincs, were placed on a 5×5 square lattice with periodic boundary conditions in lateral directions (PBC x = PBC y = 5, PBC z = 0). A saturation magnetization of M sat = 3.5 • 10 5 A/M, and exchange stiffness of A ex = 3.36 • 10 −12 J/m, were chosen based on previous work [13,23], using the same alloys. The in-plane cell size was defined as 0.5•l ex , were the exchange length, l ex is a material parameter defined by M sat and A ex [24].…”

Collective magnetic dynamics in artificial spin ice probed by ac susceptibility

“…The method lends itself to temperature and frequency dependent studies on a laboratory scale 23 , which facilitates an evaluation of well-established models, or scaling laws for the description of mesospin systems. The method can further serve as an excellent tool for the characterization of thermal dynamics, collective behaviour 40,41 and thermodynamic phase transitions in magnetic metamaterials 4,21 , such as ASIs 8,20 .…”

The effect of confinement on thermally induced fluctuations in nanomagnets

“…In order to obtain reliable spectra, each simulation is run four times with different thermal seeds, after which the resulting spectra are averaged. The spatial dependence of the magnon amplitudes can be found by taking the Fourier transform of fluctuating components via m y,z (x, y, f ) = F{m y,z (x, y, t)} [23,24]. Furthermore, the spatial dependence can be averaged out in order to obtain the spectrum, via m y,z (x, y, f ) x,y = m y,z (f ).…”