Surface anisotropy and particle size influence on hysteresis loops inLa2/3Ca1/3MnO

Abstract

Thermal and hysteretic magnetic properties of La2 /3 Ca1 /3 MnO 3 nanoparticles were studied using Monte Carlo simulations, with emphasis on the inuence of anisotropy. In this work, several nanoparticle sizes ranging from 2.32 nm to 11.58 nm were analyzed and their properties were compared to those of the bulk material. The magnetic behavior of the material was modeled using the three dimensional Heisenberg model with nearest neighbor interactions. Furthermore, both uniaxial and Néel anisotropies were considered for core and surface magnetic sites respectively. Deviations in the critical temperature and coercive eld were observed for nanoparticles when compared with those of the bulk material. In addition to these properties, the special spin congurations that arise from the competition between the exchange, anisotropy and external magnetic eld were also studied. All these eects are interpreted in terms of the surface properties such as the Néel anisotropy and the decrease in the coordination number.

Influence of Fe doped on the magnetocaloric behavior of La$_{{2}/{3}}$ Ca$_{{1}/{3}}$ Mn1−xFexO3compounds: a Monte Carlo simulation

“…The magnetic interactions are only considered between four types of ions Mn 3+ eg , Mn 3+ eg , Mn 4+ , Fe 3+ . The exchange constants for the manganese ions were reported previously [27]. However, modifications were needed in order to be consistent with the Evans model for the Hamiltonian.…”

“…Thus, the reported exchange constants J ij should be multiplied by the spin norm of the sites i and j. For this reason, the values employed here are higher than in [27]. For the bonds Fe 3+ − Mn 3+ /Mn 4+ , an effective J was used, which was obtained from previous experimental works [9,28].…”

Vegas: Software package for the atomistic simulation of magnetic materials

“…The magnetization state depends on the ratio k s /k c . When k s /k c → 0, 100, ∞ and −100, "collinear", "throttled", "hedgehog" and "artichoke" states are produced, respectively [6]. Figures 2, 6a, 6b, 8 and the inset in Figure 3a were generated using POV-Ray [21].…”

“…Because of the difficulty to solve by analytical approaches the partition function of systems represented by classical spin models, numerical simulations employing the Monte Carlo method are usually used to estimate the thermodynamic quantities of the systems. Magnetic properties of different systems, such as thin films [4], simple and core-shell nanoparticles [5,6], mixed spin systems [7], torus nanorings [8], nanotubes [9], bit-patterned media [10] and bulk materials [11,12] have been studied by Monte Carlo simulations. These atomistic simulations allow to take into account changes in the magnetization that occur at atomic scale and the finite size effects which are considerable in magnetic nanomaterials [13].…”