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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.
Highlights
Nanoparticle arrays are patterned more and more precisely with various methods, such as sub-micron sphere self-assembly lithography techniques [1,2,3,4,5], selective ion irradiation [6,7,8,9] and film growth technologies [10,11]
Noteworthy is that for odd number of particles there are two antiferromagnetic configurations with the net magnetization an odd number of particles there are two antiferromagnetic configurations with the net upwards (AF-u) and downwards (AF-d)
The study reveals the impact of the particle shapes, chain lengths and the approximations employed
Summary
Nanoparticle arrays are patterned more and more precisely with various methods, such as sub-micron sphere self-assembly lithography techniques [1,2,3,4,5], selective ion irradiation [6,7,8,9] and film growth technologies [10,11]. The systems considered: In this paper we present the evolution of configurations of the most representative one-dimensional elongated stripes and ellipsoids, consist of nanoparticles that favor the magnetization perpendicular waveguide systems, infinite and finite, of ferromagnetic particles under a variable magnetic field. A common property of all such systems is that their most stable configuration is an ellipsoids, consist of nanoparticles that favor the magnetization perpendicular to the chain due to their antiferromagnetic (AF) one. This follows from the fact that the interparticle forces are dipolar, shape anisotropy.
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