Dipolar ferromagnetism in three-dimensional superlattices of nanoparticles

Abstract

A series of atomistic finite temperature simulations on a model of an FCC lattice of maghemite nanoparticles using the stochastic Landau-Lifshitz-Gilbert (sLLG) equation are presented. The model exhibits a ferromagnetic transition that is in good agreement with theoretical expectations.The simulations also reveal an orientational disorder in the orientational order parameter for T < 0.5T c due to pinning of the surface domain walls of the nanoparticles by surface vacancies. The extent of the competition between surface pinning and dipolar interactions provides support for the conjecture that recent measurements on systems of FCC superlattices of iron-oxide nanoparticles provide evidence for dipolar ferromagnetism is discussed.

Inductive Thermal Effect of Ferrite Magnetic Nanoparticles

“…Thus, the blocking temperature of strongly interacting MNP systems is higher than that in the corresponding isolated MNP system [122,123,124]. For example, Fe 3 O 4 /SiO 2 core-shell nanoparticles with different shell thicknesses (Figure 14A–C) are prepared to understand the effect of interparticle interactions on the magnetic properties [125,126,127]. As the shell thickness decreases, the influence of interparticle dipolar interaction becomes apparent and quasi-magnetostatic states like superspin-glass (SSG) and super-ferromagnetic are observed.…”

“…Exchange coupled core-shell nanoparticles with soft core (low anisotropy, high magnetization) and hard shell (high anisotropy) or vice versa is a prominent example of an intraparticle interacting system. The core-shell nanoparticles exhibit improved magnetic properties, but more importantly they produce an intermediate magnetic anisotropy and saturation magnetization compared to both the constituents (Figure 17A) [124,125,126,127,128,129,130,131,132,133,134,135,136,137,138]. In the nanocomposite system, the magnetization of the soft magnetic phase is able to rotate coherently with that of the hard-magnetic phase, thus allowing us to utilize the advantages of soft and hard magnetic phases.…”

Toroidal Order in Magnetic Metamaterials

“…In such arrays, also referred to as artificial spin systems, first introduced in 2006 215,258 , a particular microscopic interaction on the atomic scale, e.g. magnetic exchange interaction, is substituted and mimicked by a corresponding magnetic-dipole interaction [259][260][261][262][263][264] on mesoscopic length scales. In this regard, for the study of a macroscopic phenomenon such as ferromagnetism, the underlying microscopic mechanism is irrelevant as long as the macroscopic characteristic is indistinguishable from the 'atomic prototype'.…”

Scientific Background

“…In such arrays, also referred to as artificial spin systems, first introduced in 2006 [193,236], a particular microscopic interaction on the atomic scale, e.g. magnetic exchange interaction, is substituted and mimicked by a corresponding magnetic-dipole interaction [237][238][239][240][241][242] on mesoscopic length scales. In this regard, for the study of a macroscopic phenomenon such as ferromagnetism, the underlying microscopic mechanism is irrelevant as long as the macroscopic characteristic is indistinguishable from the 'atomic prototype'.…”