Magnetic properties of Ni/Au core/shell studied by Monte Carlo simulations

The magnetic properties of ferromagnetic Ni/Au core/shell have been studied using Monte Carlo simulations within the Ising model framework. The considered Hamiltonian includes the exchange interactions between Ni–Ni, Au–Au and Ni–Au and the external magnetic field. The thermal total magnetizations and total magnetic susceptibilities of core/shell Ni/Au are computed. The critical temperature is deduced. The exchange interaction between Ni and Au atoms is obtained. In addition, the total magnetizations versus the external magnetic field and crystal filed for different temperature are also established.     

Modeling Structural and Magnetic Phase Transitions in Iron-Nickel Nanoparticles

Martensitic phase transformations and magnetovolume effects in iron-nickel alloys are intimately related. The term Invar is widely used to characterize the unusual physical properties accompanying structural and magnetic instabilities such as those observed in the vicinity of the critical composition Fe 65 Ni 35 . We discuss the crossover from bulk iron-nickel alloys to nanoparticles with respect to structural and magnetic behavior. By employing molecular-dynamics and Monte Carlo methods, we find the absence of structural instabilities in defect-free particles, a linear scaling of the austenitic transformation temperature with the reciprocal cluster radius, as well as a decrease of the magnetic transition temperature with decreasing particle size.     

Ab initio and Monte Carlo studies of phase transitions and magnetic properties of YCrO3: Heisenberg model

By using the density functional theory (DFT) and Monte Carlo simulations (MCS) with the Heisenberg model, we have studied magnetic properties of the bulk perovskite YCrO₃. The exchange couplings of the Heisenberg model and the magnetic anisotropy are investigated. The 110 direction in the crystalline structure of the compound has shown the minimum energy, it is the easy magnetic direction. Using Monte Carlo simulations, the magnetizations behavior, the effects of system parameters and the critical exponents of the compound YCrO₃ are implemented. It is shown that the bulk perovskite YCrO₃ belongs to the 3D Heisenberg universality class.     

Magnetic phase transition in Co/Cu/Ni/Cu(100) and Co/Fe/Ni/Cu(100)

Magnetic phase transitions in coupled magnetic sandwiches of Cu/Co/Cu/Ni/Cu(100) and Cu/Co/Fe/Ni/Cu(100) are investigated by photoemission electron microscopy. Element-specific magnetic domains are taken at room temperature to reveal the critical thickness at which the magnetic phase transition occurs. The results show that a coupled magnetic sandwich undergoes three types of magnetic phase transitions depending on the two ferromagnetic films' thickness. A phase diagram is constructed and explained in the process of constructing Monte Carlo simulations, which corroborate the experimental results.     

Origin of the structural and magnetic anomalies of the layered compound SrFeO2: a density functional investigation

The structural and magnetic anomaly of the layered compound SrFeO2 are examined by first-principles density functional calculations and Monte Carlo simulations. The down-spin Fe 3d electron occupies the d(z(2)) level rather than the degenerate (d(xz), d(yz)) levels, which explains the absence of a Jahn-Teller instability, the easy ab-plane magnetic anisotropy, and the observed three-dimensional (0.5, 0.5, 0.5) antiferromagnetic order. Monte Carlo simulations show that the strong interlayer spin exchange is essential for the high Néel temperature.     

嵌埋于沸石分子筛中的Fe_n团簇的磁性能研究

运用RKKY理论 ,推导了金属球形团簇间交换作用 ,并利用蒙特卡罗 (MC)方法模拟了嵌埋于沸石分子筛中的Fen 团簇体系的磁性能与团簇尺寸的关联效应。结果表明 :嵌埋式团簇体系的磁性能随团簇间距离呈震荡型 ,体系磁化强度随团簇分布密度及填充率的增大而增大 ,这对新型复合磁性材料的制备提供了参考。     

Dzyaloshinskii–Moriya interactions and magnetic texture in Fe films deposited on transition‐metal dichalcogenides

The magnetic properties of materials based on two‐dimensional transition‐metal dichalcogenides (TMDC), namely bulk Fe_1/4TaS₂ compound as well as TMDC monolayers with deposited Fe films, have been investigated by means of first‐principles DFT calculations. Changing the structure and the composition of these two‐dimensional systems resulted in considerable variations of their physical properties. For the considered systems the Dzyaloshinskii– Moriya (DM) interaction has been determined and used for the subsequent investigation of their magnetic structure using Monte Carlo simulations. Rather strong DM interactions as well as large | D ₀₁|J₀₁ ratios have been obtained in some of these materials, which can lead to the formation of skyrmionic structures varying with the strength of the applied external magnetic field. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Exchange bias in a magnetic ordered/disordered nanoparticle system: A Monte Carlo simulation study

We have employed the Monte Carlo (MC) simulation method to gain information on the exchange bias (EB) effect in nanoparticles composed of a ferromagnetic core and a disordered ferrimagnetic shell. The magnetic disorder of the shell affects the EB properties to the extent that they exhibit aging and training effects. The results of our MC simulations are in very good agreement with the experimental findings in a granular system composed of Fe nanoparticles (mean size ∼6 nm) embedded in a Fe oxide matrix confirming that the glassy nature of the shell is responsible for the observed aging and training effects.     

Magnetic field control of ferroelectric polarization and magnetization of LiCu_2O_2 compound

A spin model of LiCu2O2 compound with ground state of ellipsoidal helical structure is adopted. Taking into account the interchain coupling and exchange anisotropy, we investigate the magnetoelectric properties in a rotating magnetic field and perform the Monte Carlo simulation on a two-dimensional lattice. A prominent anisotropic response is observed in both the magnetization curve and the polarization curve, qualitatively coinciding with the behaviors that are detected in the experiment. In addition, the influences of the magnetic field with various magnitudes on polarization are also explored and analyzed in detail. As the magnetic field increases, a much smoother polarization of angle dependence is exhibited,indicating the strong correlation between the magnetic and ferroelectric orders.     

Measurements of the surface ionization in multilayered specimens

Results from experimental measurements of surface ionization, Φ(0), from multilayered specimens are presented. The studied samples consisted of Cu and C layers of different thicknesses, deposited on single‐element substrates that cover the periodic system, from Be to Bi. The surface ionization was determined by the tracer method, i.e. by measuring the characteristic x‐ray intensity emitted from an ultra‐thin tracer layer deposited on the multilayer structure and, according to Castaing's definition, dividing it by the x‐ray intensity from an equivalent, self‐supporting tracer layer. The considered tracer element was Ni, and measurements were performed for Ni Kα and Ni Lα x‐rays. Experimental results are compared with Monte Carlo simulation results generated by using the general‐purpose simulation package PENELOPE with ionization cross‐sections computed from an optical‐data model. Measured data are also compared with the predictions of an empirical analytical expression for Φ(0), which was derived from systematic Monte Carlo simulations. Copyright © 2004 John Wiley & Sons, Ltd.     

磁性单层膜磁学性质的Monte Carlo模拟

采用类Ising模型,利用Monte Carlo方法研究了磁性单层膜中退磁性偶极作用和铁磁性交换作用对系统磁学性质的影响.结果显示,随着偶极相互作用的增加,系统在低温下的磁化出现平台现象,此时磁化曲线可分为2个阶段,在低外场下,温度升高,系统易磁化,在高外场下则反之.这种新奇的磁化行为导致系统的磁熵变在低温低外场下出现大于零的反常行为.在模拟过程中,对长程力作用采用了比较精确的处理方法.     

Phase diagrams and magnetic properties of CaCu3Fe2Os2O12 quadruple perovskite: Monte Carlo study

In this paper, a Monte Carlo Simulation (MCS) has been used to study the quadruple perovskite oxide CaCu₃Fe₂Os₂O₁₂. The system has been conceived as a mixture of atoms with the magnetic moments Cu (±1/2), Fe (±5/2, ±3/2, ±1/2) and Os (±3/2, ±1/2). Phase diagrams depending on reduced exchange couplings and reduced crystal fields have been established. A stable ferromagnetic phase at the ground state has been found. Investigation of magnetic properties has been focused on the finite size analysis of magnetization and magnetic susceptibility according to reduced temperatures. Critical temperature has been calculated through simulation and the compound has been found to belong in the three-dimensional Ising model universality class.     

Electronic structure and magnetic and optical properties of double perovskite Bi2 FeCrO6 from first-principles investigation

Double perovskite Bi2 FeCrO6 , related with multiferroic BiFeO3 , is very interesting because of its strong ferroelectricity and high magnetic Curie temperature beyond room temperature. We investigate its electronic structure and magnetic and optical properties by using a full-potential density-functional method. Our optimization shows that it is a robust ferrimagnetic semiconductor. This nonmetallic phase is formed due to crystal field splitting and spin exchange splitting, in contrast to previous studies. Spin exchange constants and optical properties are calculated. Our Monte Carlo magnetic Curie temperature is 450 K, much higher than any previously calculated value and consistent with experimental results. Our study and analysis reveal that the main magnetic mechanism is an antiferromagnetic superexchange between Fe and Cr over the intermediate O atom. These results are useful in understanding such perovskite materials and exploring their potential applications.     

First Principles Investigation of the Magnetic,Magnetoelectric, and Optical Properties of Double Perovskites Containing Ions of Transition Metals LaPbTSbO<Subscript>6</Subscript> (T = Fe,Co, Ni)

Within the first principles approach implemented in the VASP package, a correlation between magnetic, electronic, polarization, and optical properties, on the one hand, and the structural ordering of cations, on the other hand, is investigated in double perovskites LaPbTSbO₆ (T = Fe, Co, Ni). Two types of cation ordering are considered: simultaneous layered (LL) and checkerboard (RR) ordering of both cations. These two types of ordering are chosen due to their significance; namely, the ordering RR is one of the most implementable types of cation ordering in double perovskites, and compounds with layered ordering can be considered as a heterostructure consisting of periodically alternating metal–nonmagnetic metal layers, which is of interest for experimental synthesis and investigation. It is found that the type of cation ordering in compounds with T = Fe and Ni radically changes the magnetic and/or electronic properties of the compound. Moreover, it is found that low-symmetry stable phases are polar for both types of cation ordering, and the values of spontaneous polarization are evaluated.     

Antiferromagnetic and semiconducting material CrNCN: Prediction from first-principles investigation

The structural stability and physical properties of CrNCN were studied using density functional theory with explicit electronic correlation (GGA+U). Calculated results indicate that the title compound, similar to MNCN (M=Mn, Fe, Co, Ni), is thermodynamically stable but mechanically unstable. Analysis of electronic and magnetic structures reveals that CrNCN is an antiferromagnetic semiconductor. However, the exact magnetic structure of CrNCN consists of an antiferromagnetic intralayer and a ferromagnetic interlayer, which differs from that of the type-II antiferromagnetic semiconductor MNCN (M=Mn, Fe, Co, Ni), which consists of a ferromagnetic intralayer and an antiferromagnetic interlayer.     

Symmetry and magnetic properties of transition metal clusters

The magnetic properties of 55-atom Fe, Co and Ni clusters are studied using the local spin-density formalism. The dependence of magnetic moment on cluster symmetry is found to be also cluster size dependent. The symmetry of cluster plays an important role in determining the charge distribution. The surface magnetism enhancement are found to be decreased from Fe to Ni.     

THEORETICAL INVESTIGATION OF ELECTRON-NEUTRAL ATOM COLLISION PROCESS AND ELECTRON TRANSPORT PARAMETERS IN DC GLOW DISCHARGE OF PLASMA WITH A TRANSVERSE MAGNETIC FIELD

A Monte Carlo simulation (MCS) technique is used to simulate the cathode sheath region of a helium dc glow discharge. In such a simulation, a nonuniform electric field and a transverse uniform magnetic field are considered. When the magnetic field intensity increases from 0 to 800 G, all types of collision considered in this paper are enhanced. This result is in agreement with the experimental result. The results also show that with the increase of magnetic field intensity, the electron transport time, the electron density increase, and the electron mean energy decreases.     

Theoretical study of the magnetic and magnetocaloric properties of the ZnFe3N antiperovskite

The antiperovskite ZnFe₃N is studied by using density functional theory calculations and Monte Carlo simulation. Based on the electronic and magnetic properties, it is found that ZnFe₃N behaves as a ferromagnetic metallic material. The exchange interactions and the magnetic anisotropy, defined as the Hamiltonian parameters of the studied system, are calculated and used in the Monte Carlo study. The second order transition at a Curie temperature T_c = 760K, reviled experimentally in a previous work, has been confirmed. The magnetic entropy change and the relative cooling power, under various applied magnetic fields are analyzed in order to evaluate the magnetocaloric effect of ZnFe₃N. The results suggest that ZnFe₃N is a good candidate for the magnetic refrigeration applications.     

Residual polarization of non-coherently backscattered linearly polarized light: the influence of the anisotropy parameter of the scattering medium

The effect of preservation of the residual polarization of backscattered light in the case of multiply scattered disordered media illumination by a linearly polarized plane wave is examined using the path-integral approach and Monte Carlo simulation. Disordered ensembles of non-interacting dielectric particles are considered as the model of scattering media. The influence of the anisotropy parameter of the scattering system on the degree of residual polarization is analysed. Experimental results obtained for various scattering systems at different wavelengths of illuminating light are in satisfactory agreement with the results of theoretical analysis and Monte Carlo simulation. The dependence of statistical properties of the polarization states of backscattered field partial components, such as probability distributions of ellipticity, on the anisotropy parameter is studied.