Multidomain and incoherent effects in magnetic nanodots

Abstract

The magnetic ground state and the magnetization reversal of aspherical nanoparticles are investigated by model calculations and micromagnetic simulations. Essential deviations from Kittel's domain theory occur for very flat and very elongated particles, for particles whose size is comparable to the domain-wall width, and when the particle shape is strongly nonellipsoidal. For example, the single-domain state of square rod is much less stable than that of comparable elongated ellipsoids, because most of the surface charge of long ellipsoids is located on the sides. Another specific feature of flat particles is suppression of the curling mode.

Magnetic properties of ultrafine‐grained cobalt samples obtained from consolidated nanopowders

“…In the case of the coarser particles, multidomains may form and the magnetization reversal may be determined by the domain‐wall motion. This behavior is in agreement with the phase diagram for small magnetic spheres reported by Skomski et al 34. It is also noticed that for Fe nanoparticles, transition from coherent to incoherent mode reversal was observed around at d c = 20 nm 35; one consequence is then the lowering of H c in comparison with that expected from coherent rotation model.…”

Reorientation phase transitions in planar arrays of dipolarly interacting ferromagnetic particles

“…A special importance have a resent attempts to use magnetic nanodot arrays for logic operations [2], for which the realization without involving multidomain elements is preferable. The well-developed numerical methods give a possibility to analyse domain wall formation and hysteretic properties in submicron particles [3] and effective anisotropies and energies of individual nanoparticles, considered as a conglomerate of atoms ( [4] and references therein). Nevertheless, the question that has arisen in almost all the experimental and theoretical works is whether each magnetic element can be considered individually or whether some kind of interaction between elements should be taken into account?…”

“…At remanence, a domain structure of submicron size particles is energetically favourable [3,26], and in the presence of magnetic field whose value is enough for the saturation, nearly uniform state establishes (in stripes it is usually of flower type [12]). Usually in elongated magnetically soft particles the value of the field establishing monodomain state is rather small [2,11].…”

Structural and angular dependence of coercivity and magnetic remanence of electrochemical ferromagnetic nanowires

“…In this work we can infer that single domain in the nanowires, and magnetization reversal modes can be modeled by homogeneous rotation when there is a critical size below which a particle remains in a single-domain state during switching, or inhomogeneous space dependent reversal θ(r) when the particle size is larger then the critical size, but still in the single-domain regime. We assume that all our samples are in the single-domain regime [9].…”

“…On the other hand for wire diameter d > d c , the reversal occurs by inhomogenous reversal (curling). Increasing further the diameter until d ≫ d c , domains may form within the wire and the magnetization reversal, thus, may occur by domain wall motion [9].…”