Magnetization reversal in amorphous Fe/Dy multilayers: a Monte Carlo study

The Monte Carlo method in the canonical ensemble is used to investigate magnetization reversal in amorphous transition metal - rare earth multilayers. Our study is based on a model containing diluted clusters which exhibit an effective uniaxial anisotropy in competition with random magnetic anisotropy in the matrix. We simulate hysteresis loops for an abrupt profile and a diffuse one obtained from atom probe tomography analyses. Our results evidence that the atom probe tomography profile favors perpendicular magnetic anisotropy in agreement with magnetic measurements. Moreover, the hysteresis loops calculated at several temperatures qualitatively agree with the experimental ones

Magnetoelectric properties of the multiferroic CuCrO2_2 studied by means of ab initio calculations and Monte Carlo simulations

Motivated by the discovery of multiferroicity in the geometrically frustrated triangular antiferromagnet CuCrO$_2$ below its N\'eel temperature $T_N$, we investigate its magnetic and ferroelectric properties using ab initio calculations and Monte Carlo simulations. Exchange interactions up to the third nearest neighbors in the $ab$ plane, inter-layer interaction and single ion anisotropy constants in CuCrO$_2$ are estimated by series of density functional theory calculations. In particular, our results evidence a hard axis along the [110] direction due to the lattice distortion that takes place along this direction below $T_N$. Our Monte Carlo simulations indicate that the system possesses a N\'eel temperature $T_N\approx27$ K very close to the ones reported experimentally ($T_N = 24-26$ K). Also we show that the ground state is a proper-screw magnetic configuration with an incommensurate propagation vector pointing along the [110] direction. Moreover, our work reports the emergence of spin helicity below $T_N$ which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model. We confirm the electric control of spin helicity by simulating $P$-$E$ hysteresis loops at various temperatures.Comment: 6 pages, 8 figure

Simulation de structures magnetiques dans des reseaux quasiperiodiques bidimensionnels

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 79195 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etude des propriétés magnétiques de super-réseaux Dy/Tb par simulations numériques Monte Carlo

L'étude des propriétés magnétiques de super-réseaux Dysprosium (Dy)/Terbium (Tb) par simulations numériques Monte Carlo a été motivée par l'existence de courbes expérimentales de variation thermique de l'aimantation, présentant un maximum et un minimum dépendant du super-réseau. Le Hamiltonien retenu est la somme d'un terme d'échange, d'un terme d'anisotropie planaire présente dans les terres rares, et d'un terme d'interaction Zeeman. L'existence de nombreux états métastables a rendu cette étude délicate, et nous a conduit à utiliser le calcul parallèle. Nos résultats montrent que la phase hélimagnétique présente dans les couches de Dy permet d'expliquer qualitativement les comportements expérimentaux observés. En particulier, la hauteur et la position des maximum et minimum sont très dépendantes du nombre de plans de Dy mais peu sensibles au nombre de plans de Tb.The investigation of magnetic properties of Dysprosium (Dy)/Terbium (Tb) superlattices by Monte Carlo simulations has been motivated by experimental curves of magnetization thermal variation, showing a maximum and a minimum that depend on the superlattice. The Hamiltonian kept is the sum of an exanche term, a planar anisotropy term, and a Zeeman interaction term. The existence of several metastable states has made this study tricky, and lead us to use parallel computing. Our results indicate that the helimagnetic phase in Dy layers allow to explain qualitatively the observed experimental behaviour. In particular, the maximum and minimum height and position are very dependent on the Dy layer thickness but not very sensitive to the Tb layer thickness.ROUEN-BU Sciences (764512102) / SudocROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Etude des propriétés magnétiques de multicouches Fe/Dy par simulations numériques Monte-Carlo

Les multicouches Fe/Dy présentent une anisotropie magnétique perpendiculaire au plan des couches qui semble fortement corrélée à la formation d un alliage amorphe Fe-Dy à l interface. Le but de ce travail est d étudier les propriétés magnétiques de ces systèmes par simulations Monte Carlo pour différents types d'interfaces. Nous mettons en évidence l existence d un profil d aimantation inhomogène en épaisseur qui dépend du profil de concentration. Nos résultats sont en bon accord avec les résultats expérimentaux, en particulier sur l ouverture des cycles d hystérésis lorsque le champ est appliqué dans le plan des couches en raison de l influence de l anisotropie aléatoire. Pour un champ magnétique appliqué perpendiculairement au plan des couches, les cycles d hystérésis sont caractéristiques d'une anisotropie perpendiculaire.Fe/Dy multilayers exhibit perpendicular magnetic anisotropy which is correlated to the existence of an Fe-Dy alloy at the interface. The aim of this work is to investigate the magnetic properties of these systems by Monte Carlo simulations for different concentration profiles. We evidence an inhomogeneous magnetisation profile related to the concentration profile. Our results give a good agreement with experimental results, in particular our model allow an explanation of the hard direction hysteresis loop opening due to the random anisotropy. When the field is applied perpendicular to the layer, the hysteresis loops of the diffuse profile are characteristic of a perpendicular anisotropy.ROUEN-BU Sciences (764512102) / SudocROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Atomic modeling of the microstructure evolution in Ni-Fe alloys (correlation between magnetic and structural properties)

Les alliages Fe-Ni sont largement utilisés en raison de leurs propriétés intéressantes fondamentales découlant de la coexistence de l'orde chimique et l'ordre magnétique. L'objectif de ce travail était de comprendre l influence mutuelle de ces deux mises en ordre sur les propriétés thermodynamiques d équilibre et la cinétique dans les alliages Permalloy (Ni3Fe). A partir de simulations Monte Carlo et de type Champ Moyen, nous avons mis en évidence l'effet des interactions magnétiques sur la température de transition ordre/désordre et réciproquement, l'influence des interactions chimiques sur la température de Curie. La cinétique de précipitation a été étudiée à partir de l'équation de microdiffusion d Onsager en utilisant les paramètres déduits de calculs ab-initio. Ces simulations ont montré l'influence des interactions magnétiques sur la formation des particules L12 stable. Les deux types de simulations, thermodynamique et cinétique, ont donc confirmé l'importance de prendre en compte simultanément les interactions magnétiques et chimiques. Les résultats obtenus concordent bien avec les données expérimentales disponibles.Fe-Ni alloys are widely used due to their interesting fundamental properties which arise from the coexistence of the chemical and magnetic order. The aim of this work was to understand the mutual influence of these two types of ordering on the thermodynamic and kinetic processes in Permalloys (Ni3Fe). From Monte Carlo and Mean Field simulations the effect of the magnetic interactions on the order/disorder transition temperature has been observed, and reciprocally the influence of the chemical interactions on the Curie temperature. The kinetics of the precipitation has been studied by means of the Onsager microdiffusion equation using parameters extracted from ab-initio calculations. These simulations have evidenced the influence of the magnetic interactions on the formation of the stable L12 particles. Both thermodynamic and kinetic investigations have confirmed the importance of taking into account simultaneously both magnetic and chemical interactions. The obtained results agree well with the available experimental data.ROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Magnetisation switching in a ferromagnetic Heisenberg nanoparticle with uniaxial anisotropy: A Monte Carlo investigation

We investigate the thermal activated magnetisation reversal in a single ferromagneticnanoparticle with uniaxial anisotropy using Monte Carlo simulations. The aim of this work is toreproduce the reversal magnetisation by uniform rotation at very low temperature in the highenergy barrier hypothesis, thatis to realize the Néel-Brown model. For this purpose we have considered a simple cubicnanoparticle where each site is occupied by a classical Heisenberg spin. The Hamiltonian isthe sum of an exchange interaction term, a single-ion anisotropy term and a Zeemaninteraction term. Our numerical data of the thermal variation of the switching field arecompared to an approximated expression and previous experimental results on Co nanoparticles

Magnetization reversal in amorphous Fe/Dy multilayers: a Monte Carlo study

International audienceThe Monte Carlo method in the canonical ensemble is used to investigate magnetization reversal in amorphous transition metal - rare earth multilayers. Our study is based on a model containing diluted clusters which exhibit an effective uniaxial anisotropy in competition with random magnetic anisotropy in the matrix. We simulate hysteresis loops for an abrupt profile and a diffuse one obtained from atom probe tomography analyses. Our results evidence that the atom probe tomography profile favors perpendicular magnetic anisotropy in agreement with magnetic measurements. Moreover, the hysteresis loops calculated at several temperatures qualitatively agree with the experimental ones

Monte Carlo investigation of the magnetic anisotropy in Fe/Dy multilayers

International audienceBy Monte Carlo simulations in the canonical ensemble, we have studied the magnetic anisotropy in Fe/Dy amorphous multilayers. This work has been motivated by experimental results which show a clear correlation between the magnetic perpendicular anisotropy and the substrate temperature during elaboration of the samples. Our aim is to relate macroscopic magnetic properties of the multilayers to their structure, more precisely their concentration profile. Our model is based on concentration dependent exchange interactions and spin values, on random magnetic anisotropy and on the existence of locally ordered clusters that leads to a perpendicular magnetisation. Our results evidence that a compensation point occurs in the case of an abrupt concentration profile. Moreover, an increase of the noncollinearity of the atomic moments has been evidenced when the Dy anisotropy constant value grows. We have also shown the existence of inhomogeneous magnetisation profiles along the samples which are related to the concentration profiles