Effect Of Magnetic Interactions Research Articles

Structural and magnetic characterizations of Co2MnO4 doped with Cr, Mn, Fe and Cu

The structural and magnetic properties of Co2-xMxMnO4 (M= Cr, Mn, Fe and Cu) samples are investigated. Element substitution does not change the cubic lattice structure within a range of concentrations. There is a structural transition from cubic to tetragonal with the excessive addition of Mn atoms. The site preference of transition metal atoms influences the interatomic interactions in the oxide system. The interatomic interactions of Co2MnO4 and CoMn2O4 samples are analyzed though ZFC/FC curves, the transition temperatures of which are attributed to the combined effect of magnetic interactions in different sublattices. The magnetic structure is restructured by atomic substitution and site preference, resulting in the compositional dependence of magnetic properties.

Relativistic splitting of surface states at Si-terminated surfaces of the layered intermetallic compoundsRT2Si2(R=rare earth;T=Ir, Rh)

We present an effective model for surface states at the Si-terminated (001) surface of ternary rare earth (R) intermetallic compounds ${\mathit{RT}}_{2}{\mathrm{Si}}_{2}$ with the transition metal element $T$ = Ir or Rh. The model is based on a fully ab initio derivation of the relativistic $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ Hamiltonian and is thereby capable of accurately reproducing the spin polarization of the spin-orbit split surface states, which is very different from the classical Rashba effect. The reliable treatment of spin in our model enables a predictive analysis of the effect of magnetic exchange interaction of the surface-state electrons with ferromagnetically ordered $4f$ moments of the subsurface rare-earth layer in the magnetic phases of the ${\mathit{RT}}_{2}{\mathrm{Si}}_{2}$ compounds.

Curvature couplings of massless fermions in analog gravity

Bogoliubov quasiparticles moving in the background of superfluid He3-A see an apparently curved space–time metric when the background superfluid vacuum is in motion. We study how this curvature couples with the spins of the effectively massless quasiparticles. First, we set up the problem in null Fermi coordinates for radial as well as circular geodesics and then use it in the context of the analog metric seen by the quasiparticles. We obtain an effective magnetic interaction due to curvature coupling, and provide numerical estimates. Some possible implications of these results are then pointed out.

Magnetoelectric Radical Hydrocarbons.

The molecular radicals, systems with unpaired electrons of open-shell electronic structures, set the stage for a multidisciplinary science frontier relevant to the cooperative magnetic exchange interaction and magnetoelectric effect. Here ferroelectricity together with magnetic spin exchange coupling in molecular radical hydrocarbon solids is reported, representing a new class of magnetoelectrics. Electronic correlation through radical-radical interactions plays a decisive role in the coupling between magnetic and charge orders. A substantial photoconductance and visible-light photovoltaic effect are found in radical hydrocarbons. The ability to simultaneously control and retrieve the changes in magnetic and electrical responses opens up a new breadth of applications, such as radical magnetoelectrics, magnets, and optoelectronics.

The magnetic dipole-dipole interaction effect on the magnetic hysteresis at zero temperature in nanoparticles randomly dispersed within a plane

Abstract The dipole-dipole interaction effect on the magnetic hysteresis of nanoparticles randomly dispersed within a plane is studied by micromagnetic simulation. The dependence of the coercive field with the concentration of nanoparticles varies from nonlinear and monotonic to non-monotonic dependence with a maximum at a certain concentration. It happens when the ratio of the magnetic anisotropy constant to the maximal dipole energy changes from value much larger than 1 to the value much less than unity.

Modelling the effect of different core sizes and magnetic interactions inside magnetic nanoparticles on hyperthermia performance

Abstract We present experimental intrinsic loss power (ILP) values, measured at an excitation frequency of 1 MHz and at relatively low field amplitudes of 3.4–9.9 kA/m, as a function of the mean core diameter, for selected magnetic nanoparticles (MNPs). The mean core sizes ranged from ca. 8 nm to 31 nm. Transmission electron microscopy indicated that those with smaller core sizes (less than ca. 22 nm) were single-core MNPs, while those with larger core sizes (ca. 29 nm to 31 nm) were multi-core MNPs. The ILP data showed a peak at core sizes of ca. 20 nm. We show here that this behaviour correlates well with the predicted ILP values obtained using either a non-interacting Debye model, or via dynamic Monte-Carlo simulations, the latter including core-core magnetic interactions for the multi-core particles. This alignment of the models is a consequence of the low field amplitudes used. We also present interesting results showing that the core-core interactions affect the ILP value differently depending on the mean core size.

Quantum correlations and entropic uncertainty relation in a three-qubit spin chain under the effect of magnetic field and DM interaction

In this paper, we study the thermal dynamics of quantum correlations and uncertainty relation in a three-qubit spin chain under the effect of Hamiltonian XY model, Dzyaloshinskii–Moriya (DM) interaction and external magnetic field. The results show that quantum correlations behave contrary to uncertainty under the effect of thermal dynamics and external magnetic field. However, they evolve in the same way under effect of DM interaction and spin coupling. DM interaction, magnetic field and spin coupling enhance quantum correlations.

Magnetic hyperthermia in a system of ferromagnetic particles, frozen in a carrier medium: Effect of interparticle interactions

A theoretical study of magnetic hyperthermia, produced by ferromagnetic particles, frozen in a carrier medium, is presented. The main emphasis of the analysis is on the effects of magnetic interaction between the particles. Any Brownian effects, including the thermally activated N\'eel remagnetization of the particle, are neglected. In contrast to the N\'eel remagnetization, the heating is the most efficient when the axes of easy magnetization of the particles are perpendicular to the field direction; magnetic interaction between the particles enhances the heat production.

Magnetization Dynamics and Energy Dissipation of Interacting Magnetic Nanoparticles in Alternating Magnetic Fields with and without a Static Bias Field

The effect of interparticle interactions on the magnetization dynamics and energy dissipation rates of spherical single-domain magnetically blocked nanoparticles in static and alternating magnetic fields (AMFs) was studied using Brownian dynamics simulations. For the case of an applied static magnetic field, simulation results suggest that the effective magnetic diameter of interacting nanoparticles determined by fitting the equilibrium magnetization of the particles to the Langevin function differs from the actual magnetic diameter used in the simulations. Parametrically, magnetorelaxometry was studied in simulations where a static magnetic field was suddenly applied or suppressed for various strengths of magnetic interactions. The results show that strong magnetic interactions result in longer chain-like particle aggregates and eventually longer characteristic relaxation time of the particles. For the case of applied AMF with and without a static bias magnetic field, the magnetic response of interacting nanoparticles was analyzed in terms of the harmonic spectrum of particle magnetization and dynamic hysteresis loops, whereas the energy dissipation of the particles was studied in terms of the calculated specific absorption rate (SAR). Results suggest that the effect of magnetic interactions on the SAR varies significantly depending on the amplitude and frequency of the AMF and the intensity of the bias field. These computational studies provide insight into the role of particle–particle interactions on the performance of magnetic nanoparticles for applications in magnetic hyperthermia and magnetic particle imaging.

Fluctuation-induced Néel and Bloch skyrmions at topological insulator surfaces

Ferromagnets in contact with a topological insulator have become appealing candidates for spintronics due to the presence of Dirac surface states with spin-momentum locking. Because of this bilayer Bi$_2$Se$_3$-EuS structures, for instance, show a finite magnetization at the interface at temperatures well exceeding the Curie temperature of bulk EuS. Here we determine theoretically the effective magnetic interactions at a topological insulator-ferromagnet interface {\it above} the magnetic ordering temperature. We show that by integrating out the Dirac fermion fluctuations an effective Dzyaloshinskii-Moriya interaction and magnetic charging interaction emerge. As a result individual magnetic skyrmions and extended skyrmion lattices can form at interfaces of ferromagnets and topological insulators, the first indications of which have been very recently observed experimentally.

Quantum phase transition in a realistic double-quantum-dot system

Observing quantum phase transitions in mesoscopic systems is a daunting task, thwarted by the difficulty of experimentally varying the magnetic interactions, the typical driving force behind these phase transitions. Here we demonstrate that in realistic coupled double-dot systems, the level energy difference between the two dots, which can be easily tuned experimentally, can drive the system through a phase transition, when its value crosses the difference between the intra- and inter-dot Coulomb repulsion. Using the numerical renormalization group and the semi-analytic slave-boson mean-field theory, we study the nature of this phase transition, and demonstrate, by mapping the Hamiltonian into an even-odd basis, that indeed the competition between the dot level energy difference and the difference in repulsion energies governs the sign and magnitude of the effective magnetic interaction. The observational consequences of this transition are discussed.

Three-axis MEMS DC magnetic sensor using magnetic force interaction with the piezoelectric effect

In this paper, we report a novel three-axis MEMS DC magnetic sensor using magnetic force interaction and piezoelectric effect. The sensor includes a back-side-etched silicon diaphragm, a sol-gel PZT thin film with electrodes, and two patterned electroplated Ni thick films. Each patterned Ni film has specific magnetization direction, defined as specific sensing area. As a DC magnetic fields is applied to the sensor, impulse magnetic force and torque are induced to deflect and twist specific Ni films, respectively. Through the mechanical coupling between the Ni films and the PZT film, the deflection and bending are transmitted to the PZT film to produce piezoelectric peak voltages. Experimental results show that, by analysing full duration and half maximum of voltage outputs produced in two sensing areas, the sensor is able to sense three-axial DC magnetic fields.

Dextran coated magnetite high susceptibility nanoparticles for hyperthermia applications

In this study, the magnetic fluid with various concentrations of well-dispersed dextran coated Fe3O4 nanoparticles were synthesized for hyperthermia application. The dextran-coated colloidal suspension, in the form of clusters of several Fe3O4 nanoparticles, maintains superparamagnetic behavior of Fe3O4 with the saturation magnetization of 59 emu/g at room temperature. The coated nanoparticles dispersed in aqueous medium agglomerate to form a monodisperse system and its average polydispersity index is 0.096. The inter-particle interaction caused the large susceptibility (1239 emu/gT) in dextran coated Fe3O4 nanoparticles. Effect of magnetic dipole interaction between the clusters on magnetic properties and heat capacity was examined by comparing specific loss power (SLP) of magnetic fluids at different Fe3O4 concentration. The intrinsic loss power (ILP) parameter increases with decreasing concentration of the dextran coated Fe3O4 and reaches the value of 15.6 nHm2/kg, which is 35% better than the best commercial equivalents. This result clearly shows that magnetic interaction between coated particles strongly influences induction heating efficiency of magnetic fluid. The in vitro toxicity experiments of magnetic fluids with Madin Darby Canine Kidney cells prove that our obtained magnetic fluids are promising for the hyperthermia cancer treatment application.

Comparative study about the cantilever generators with different curve fixtures

Magnetic interaction and pre-stress effect are two regular ways of introducing nonlinearities for wideband energy harvesting. However, the susceptibility to the fabrication and assembling makes it a tough job to exactly tune the magnetic field distribution and the preload as desired for the purpose of avoiding large deviation from design and model, especially in the micro-electro-mechanical systems scale. The nonlinear generator by introducing a curve fixture to the cantilever beam instead of the rectangular fixture presents a feasible and simple solution with good micro-electro-mechanical system fabrication compatibility. In this article, three prototypes of with different curve fixtures with the same size requirement are fabricated for detailing the influence of the selection of the fixture curve. Experimental and numerical investigations reveal that the generator has better performance when the nonlinear stiffness introduced by the curve fixture is smooth, especially in the case of no linear stiffness segment.

Statistical analysis of phase formation in 2D colloidal systems

.Colloidal systems offer unique opportunities for the study of phase formation and structure since their characteristic length scales are accessible to visible light. As a model system the two-dimensional assembly of colloidal magnetic and non-magnetic particles dispersed in a ferrofluid (FF) matrix is studied by transmission optical microscopy. We present a method to statistically evaluate images with thousands of particles and map phases by extraction of local variables. Different lattice structures and long-range connected branching chains are observed, when tuning the effective magnetic interaction and varying particle ratios.Graphical abstract

Effective Anisotropic Interactions in Spin Pairs Containing High-Spin Ions with Large Zero-Field Splitting.

Analytic and numeric derivations are made of the effective exchange and dipolar magnetic interactions between spin pairs containing S = 3/2 ions, such as high-spin Co(II), S = 5/2 ions, such as high-spin Fe(III) ions, experiencing zero-field splittings much larger than the interion interactions, or J = 15/2 ions such as Dy(III) with crystal-field splittings much larger than the interion interaction. These formulas allow for a simpler analysis of the magnetic properties of dimers containing high-spin ions.

Nonseparable frequency dependence of the two-particle vertex in interacting fermion systems

We derive functional flow equations for the two-particle vertex and the self-energy in interacting fermion systems which capture the full frequency dependence of both quantities. The equations are applied to the hole-doped two-dimensional Hubbard model as a prototype system with entangled magnetic, charge and pairing fluctuations. Each fluctuation channel acquires substantial dependencies on all three Matsubara frequencies, such that the frequency dependence of the vertex cannot be accurately represented by a channel sum with only one frequency variable in each term. At the temperatures we are able to access, the leading instabilities are mostly antiferromagnetic, with an incommensurate wave vector. However, at large doping, a divergence in the charge channel occurs at a finite frequency transfer, if the vertex flow is computed without self-energy feedback. This enigmatic instability was already observed in a calculation by Husemann et al. [Phys. Rev. B 85, 075121 (2012)], who used an approximate separable ansatz for the frequency dependence of the vertex. We identify a simple mechanism for this instability in terms of a random phase approximation for the charge channel with a frequency dependent effective magnetic interaction as input. In spite of the strong momentum and frequency dependence of the vertex, the self-energy has a Fermi liquid form. At the moderate interaction strength where our approach is applicable, we obtain a moderate reduction of the quasi-particle weight and a sizable decay rate with a pronounced momentum dependence. Nevertheless, the self-energy feedback into the vertex flow turns out to be crucial, as it suppresses the unphysical finite frequency charge instability.

The effects of transverse magnetic field and local electronic interaction on thermoelectric properties of monolayer graphene

We study the effects of a transverse magnetic field and electron doping on the thermoelectric properties of monolayer graphene in the context of Hubbard model at the antiferromagnetic sector. In particular, the temperature dependence of thermal conductivity and Seebeck coefficient has been investigated. Mean field approximation has been employed in order to obtain the electronic spectrum of the system in the presence of local electron-electron interaction. Our results show the peak in thermal conductivity moves to higher temperatures with increase of both chemical potential and Hubbard parameter. Moreover the increase of magnetic field leads to shift of peak in temperature dependence of thermal conductivity to higher temperatures. Finally the behavior of Seebeck coefficient in terms of temperature has been studied and the effects of magnetic field and Hubbard parameter on this coefficient have been investigated in details.

Effective demagnetizing tensors in arrays of magnetic nanopillars

A model describing the effect of magnetic dipolar interactions on the susceptibility of magnetic nanopillars is presented. It is an extension of a recently reported model for three-dimensional randomlike dispersions of nearly spherical nanoparticles in equilibrium [S\'anchez et al., Phys. Rev. B 95, 134421 (2017)], to well-ordered arrays of nanoparticles out of equilibrium. To test it, a high-quality benchmark consisting of a two-dimensional hexagonal arrangement of quasi-identical parallel nickel nanopillars embedded in a porous alumina template was fabricated. This model is based on an effective demagnetizing tensor, which only depends on a few morphological parameters of the sample, as the nearest-neighbor distance between pillars and the volume fraction of pillars in the specimen. It allows us to obtain the nanopillar intrinsic susceptibility tensor from the magnetic response of the nanopillar ensemble. The values of the in-plane and normal-to-plane susceptibility of the sample are successfully predicted by the model. Furthermore, the model reproduces the susceptibility in the applied field direction, measured for different applied field angles. In this way, it provides a simple and accurate treatment to account for the complex magnetic effects produced by dipolar interactions.

Dipolar magnetic interaction effects in 2D hexagonal array of cobalt hollow-spheres

Planar arrangements of cobalt hollow-spheres were studied by means of micromagnetic simulation. The calculated coercivity values are in correspondence with the reported experimental data. Dipole energy effects are determinant and more significant if thickness decreases. We observed the formation of some vortex and onion configurations, solutions for individual hollow-sphere, even so there is predominance of non-homogeneous reversal. This confirms that solutions for individual spheres are not efficient in the analysis of arrays.