Finite Length Effects on Switching Mechanisms in Chains of Magnetic Particles

Abstract

Periodic systems of magnetic nanoparticles are now of interest as they support GHz spin waves. Their equilibrium configurations, switchable with the external magnetic field, are crucial for such applications. We study infinite and finite chains of particles of two shapes (i) ellipsoidal and (ii) rectangular stripes with long axes perpendicular to the chain axis. A variable magnetic field is applied parallel to the long axes. Micromagnetic simulations are compared with the corresponding discrete spin models (Stoner-Wohlfarth model, S-W). An antiferromagnetic configuration is the ground state for all the systems at vanishing field but a ferromagnetic configuration occurs when the field is strong enough. The switching of the infinite chains to the reversed ferromagnetic configuration proceeds directly for the ellipsoids and by an intermediate configuration, in which the magnetization within the particle is non-uniform, in the case of the stripes. The non-uniform configurations are well represented by tilted states in S-W model. Important differences are found in the finite analogs: the switching of ellipsoids becomes multistage and starts from the innermost particles relatively well reproduced with S-W model, whereas the reversal of the stripes, starts from the outermost particles and has no analog in S-W model. Practical consequences of the findings are discussed.

Competing Magnetocrystalline and Shape Anisotropy in Thin Nanoparticles

“…The fundamental magnetic parameters of the constituent compounds relevan present studies are the saturation magnetisation and exchange stiffness. The sat magnetisation and exchange stiffness constant of permalloy are equal to 𝑀 = 89 and 𝐴 = 1.3 × 10 J/m, respectively [27,37]. The analogous characteristics for nal cobalt are 𝑀 = 1390 kA/m, 𝐴 = 1.3 × 10 J/m [38].…”

“…Magnetic particles of elongated morphology show a tendency to align the magnetic moments parallel to their long axes. In many aspects, such particles behave similarly or analogously to single magnetic moments, which has earned them the name macrospins [26,27]. Due to the rapid progress in nanofabrication, such an extrinsic property can be rationally and precisely tuned through surface-and shape-controlled synthesis and help to achieve more specific magnetic characteristics for the material [28,29].…”

A Low-Dimensional Layout of Magnetic Units as Nano-Systems of Combinatorial Logic: Numerical Simulations

“…The general magnetic behavior of the system presented in Figure 1 was analyzed in detail in our previous work [ 20 ]. The present paper is a continuation of our earlier investigations.…”

“…A detailed description of the model and details of the simulations were described in our earlier article [ 20 ]. In short, we assumed that a magnetic field is applied to the chains in the Y direction (parallel to the long axes of the magnetic units).…”