Micromagnetic Investigation Of Magnetic Nanostructures

Static and dynamic magnetic properties of nanostructures, such as:ring, dot, prism, and wires arrays, are studied using three-dimensional micromagnetic simulations.Three mainly different systems of ring are studied:1) the smaller outer radius of ring, i.e., outer radius R=10 nm, inner radius r=6 nm, thickness L=2…500 nm. The emphasis is placed on the effect of ring thickness on the magnetization reversal and dynamic susceptibility spectra of the out-of-plane state. The investigated systems show two major resonance modes associated with volume and shape resonance modes, corresponding to the low and the high resonance frequency, respectively. When L is below Lc, only the shape resonance mode is seen with a frequency predicted using the Kittel's equation and demagnetization factor calculated for a ring. At sufficiently large L, the frequency of the volume mode converges to that of the Kittel prediction. For other lengths, however, neither the low resonance frequency nor the high resonance frequency agrees with the Kittel's equation. A weighted average resonance frequency fa(i) that contains two major modes is introduced and shows the same trend as the results predicted by the Kittel's equation for all lengths. The frequencies of volume and shape resonance modes have also been investigated by changing the exchange stiffness constant (A) and the saturation magnetization (Ms). Moreover, the results of ring, pillar, and prism have been compared.2) The small outer radius of ring, i.e., R=15 nm, r=9 nm, t=2…35 nm. There are four states for rings depending on the thickness:in-plane, vortex, H, and out-of-plane states. Effect of different states on the dynamic susceptibility spectra of rings is fully discussed in this section.3) The large outer radius of ring, i.e., R=100 nm, r=50 nm, t=10…200 nm. The main features of spectra (number of resonances, frequencies, and intensities) have been investigated and spatial maps of the susceptibility have enabled identification of various resonance modes, including surface, volume, edge, and mixed edge and volume modes. Magnetostatic interaction and dynamic susceptibilities of permalloy nanowires arrays (20×500×-500 nm3, R=10 nm,L=500 nm, d=2.5…30 nm) have been studied using micromagnetic simulations. By choosing different interwire distances, remanent states, and the exciting field direction, the effects of magnetostatic interaction on resonance frequencies are investigated in detail. We also compared to theoretical analysis with the simulation results.