Dynamic response of an artificial square spin ice

Abstract

Magnetization dynamics in an artificial square spin-ice lattice made of Ni80Fe20 with magnetic field applied in the lattice plane is investigated by broadband ferromagnetic resonance spectroscopy. The experimentally observed dispersion shows a rich spectrum of modes corresponding to different magnetization states. These magnetization states are determined by exchange and dipolar interaction between individual islands, as is confirmed by a semianalytical model. In the low field regime below 400 Oe a hysteretic behavior in the mode spectrum is found. Micromagnetic simulations reveal that the origin of the observed spectra is due to the initialization of different magnetization states of individual nanomagnets. Our results indicate that it might be possible to determine the spin-ice state by resonance experiments and are a first step towards the understanding of artificial geometrically frustrated magnetic systems in the high-frequency regime.Frustrated magnetic systems, such as spin ices, have been of scientific interest for a long time due to their highly degenerated ground states, which result in complex magnetic ordering and collective behavior [1][2][3][4][5]. In contrast to the prototypical crystalline materials that started the exploration of spin-ice systems, such as the pyrochlores Dy 2 Ti 2 O 7 , Ho 2 Ti 2 O 7 and Ho 2 Sn 2 O 7 [6,7], artificially structured spin-ice lattices offer the unique opportunity to control and engineer the interactions between the elements by their geometric properties and orientation [1,8,9]. Another outstanding advantage of artificial spin ices is that the magnetization state of each individual spin (i.e., macrospin/single domain magnetic particle) is directly accessible through magnetic microscopy (e.g., scanning probe, electron, optical or X-ray microscopy). The 16 possible magnetization configurations of a square spin ice are shown in Fig. 1(a).Spin dynamics in magnonic crystals, materials with periodic perturbations or variations in one of the magnetic properties of the system, have been extensively investigated [10-13]. One-and two-dimensional magnonic crystals were studied and the research community paid particular attention to nano-structured materials [10], such as chains of dots or arrays of discs [14], antidot lattices with different shapes and alignments [15][16][17], gratings or nanostripes [18], etc.Although artificial spin ices offer a fascinating playground to investigate how specific magnetization states of individual islands or defects can affect the collective spin dynamics, there are only very few works on dynamics in the GHz-regime [19,20] reported. Sklenar et al. show broadband ferromagnetic resonance (FMR) measurements on an artificial bicomponent square spin-ice lattice utilizing a macroscopic meanderline approach and find a field-dependent behavior in remanence where interactions between individual elements presumably play a less important role. Furthermore, the geometrical arrangement of the structures in the artificial lattice leads to frustration by d...

Thermally induced magnetic relaxation in square artificial spin ice

“…Artificial ferroic systems with tunable dynamical properties can be designed by considering different materials and geometries rather than being limited just by microscopic material properties25. This facilitates the study of dynamics in many-body systems on adjustable length, energy and time scales, enabling the design of new devices with tailored electromagnetic properties in the relevant frequency regimes2627. The new emergent dynamics of mesoscale objects, such as the patterned nanomagnets comprising the artificial spin ice arrays and the related magnetic charge defects due to thermal fluctuations, further highlight the promise these systems offer in the design of reconfigurable magnonic devices2225.…”

Angular-dependent magnetization dynamics of kagome artificial spin ice incorporating topological defects

“…The applied science community is interested in utilization of ASIs in magnonics-related applications [10]. Indeed, magnonic properties were reported for different ASIs [11][12][13]; however, angular dependencies and the regime of the twostep magnetization reversal were not studied in detail. It is interesting whether such a two-step magnetization process gives rise to distinct resonances, and whether the TDs and their resonances are stable against field cycles.…”

Efficient charge-spin conversion and magnetization switching through the Rashba effect at topological-insulator/Ag interfaces

“…interface Rashba system reported recently [35], suggesting that the Bi2Se3/Ag interface effect is most likely to be the interfacial Rashba effect. We also extracted /   ratio in the Ag/CoFeB control samples without the Bi2Se3/Ag interface in Fig.…”

“…To further explore the role of the Bi2Se3/Ag interface in the charge-to-spin conversion, we analyze the ratio of in-plane and out-of-plane torque ( /   ) [35] for Bi2Se3/Ag/CoFeB samples.…”