Magnetic properties of Ni/Au core/shell studied by Monte Carlo simulations
Introduction
Metallic nanoparticles (NPs) or clusters, aggregates of several to millions atoms, have been emerging as a new type of important functional material [1]. They exhibit distinct properties (optical, electronic, magnetic, and so on) from those of individual atoms or their bulk counterparts due to the quantum-size and surface effects. More importantly, the properties are usually size- and structure-dependent, which have attracted tremendous research attention from either basic science or application viewpoints during the last two decades [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. The preparation of some magnetic metal nanoparticles such as iron, and nickel is relatively more difficult because they are prone to be oxidation [15]. However, although various kinds of core/shell nanoparticles have been prepared through a variety of methods, the investigation about how to control the core diameter and the shell thickness is very limited. Furthermore, because the core diameter and shell thickness of the core/shell nanoparticles has a great effect on the magnetic [4] properties, and so on, to control the dimensions of the core and shell has a significant meaning. The gold loading is very low for Au-covered Ni core/shell and a synergistic effect exits between Au and Ni in the core/shell [16], [17]. On the other hand, the Monte Carlo simulations are carried out to investigate the magnetic properties of nano-systems [18], [19], [20]. The magnetic properties of Ni/Au core/shell are studied by [21], [22]. The synthesis and super-paramagnetic properties of neodymium ferrites nanorods are established by [23]. Recently developed experimental and theoretical studies [24], [25], [26], [27] have shown that clusters of several bimetallic systems, such as AuAg, AgNi, AgPd, AgCu, present preferentially core–shell structures.
In this study, we are interested in the magnetic properties of core/shell Ni/Au (see Fig. 1) with a fixed size and sites. The thermal total magnetizations and total magnetic susceptibilities are given in Fig. 2 for a zero crystal field and a zero external magnetic field of Au/Ni core/shell. Total magnetizations versus the external magnetic field of Au/Ni core/shell for and for different temperatures are given in Figs. 3(a) and 3(b). Figs. 4(a) and 4(b) show the variation of the total magnetization versus the exchange interactions (). The total magnetizations versus the crystal filed (Δ) for different values of the temperature of Au/Ni core/shell is given in Fig. 5 for different temperature.
Section snippets
Theoretical model
The studied system is described by the Hamiltonian of the Ising model including nearest neighbors interactions and external magnetic field: where stand for the first nearest neighbor sites i and j. , and , are the first exchange interaction between the atoms: Ni–Ni, Au–Au and Ni–Au, respectively. The external magnetic field h is applied over all the spins of the Ni/Au in the z-direction
Monte Carlo simulations
We apply a standard sampling method to simulate the Hamiltonian given by Eq. (1). Cyclic boundary conditions on the Ni/Au core/shell lattice were imposed and the configurations were generated by sequentially traversing the lattice and making single-spin flip attempts. The flips are accepted or rejected according to a heat-bath algorithm under the Metropolis approximation (see Fig. 6 – flow chart of Monte Carlo simulations).
Cyclic conditions on the Au/Ni core/shell are used for a fixed
Results and discussions
We presented in Fig. 2 the thermal total magnetizations and total magnetic susceptibilities for a zero crystal field and a zero external magnetic field of Au/Ni core/shell. The sharp maximum in the total magnetic susceptibilities curves indicated a clear blocking behavior of the samples. The critical temperature increases from 6.28 to 15.88 K. The last value is comparable with those given by Refs. [15], [29], [30] ( [29]). This increasing indicating the coating enhanced the
Conclusion
The magnetic properties of ferromagnetic Au/Ni core/shell have been investigated using Monte Carlo simulations within the Ising model framework. The critical temperature of Au/Ni core/shell is obtained and comparable with those obtained by experiment results. The magnetic moment decreases when the temperature and the exchange interaction () decrease. This reduction in moment might stem from the small size effect, the oxidation of the Ni cores, the increased surface of the Au/Ni
References (32)
- et al.
Synth. Met.
(2005) - et al.
J. Catal.
(1989) - et al.
J. Alloys Compd.
(2009) - et al.
Electrochim. Acta
(2010) - et al.
Electrochem. Commun.
(2007) - et al.
J. Magn. Magn. Mater.
(2012) - et al.
Solid State Commun.
(2013) - et al.
J. Alloys Compd.
(2013) - et al.
Phys. Lett. A
(2012) Atomic and Molecular Clusters
(2002)
J. Mater. Chem.
J. Mater. Chem.
J. Mater. Chem.
Chem. Commun.
Science
Annu. Rev. Mater. Sci.
Cited by (44)
Magnetic features of hybrid transition metal-rare earth nanoparticles: Monte Carlo simulations
2023, Physica B: Condensed MatterEffect of Zr on microstructure and properties of TC4 alloy fabricated by laser additive manufacturing
2023, Journal of Materials Research and TechnologyPrediction of magnetic properties of a single-molecule magnetic metallofullerene cluster DySc<inf>2</inf>N@C<inf>80</inf>
2022, Physica B: Condensed MatterDynamic magnetic properties of borophene nanoribbons with core-shell structure: Monte Carlo study
2022, Journal of Magnetism and Magnetic MaterialsCitation Excerpt :For instance, Z. Fadil et al. explored dielectric properties of a monolayer nano-graphyne structure and the ground state phase diagrams were given [27]. They also studied the effect of the RKKY interaction on the magnetic properties of the bi-layer graphyne structure [28] and Ni/Au with core/shell structure [29]. It is found that the transition temperature increases when decreasing the number of non-magnetic layers.
Electronic and magnetic properties of CoFe2O4 nanostructures: An ab-initio and Monte Carlo study
2022, Physica B: Condensed Matter