Role Of Magnetic Interactions Research Articles

Particles with magnetic dipole moment orbiting magnetized Schwarzschild black holes: Applications to orbits of hot-spots around Sgr A*

We study the circular motion of particles with magnetic dipole moment around Schwarzschild black holes immersed in external asymptotically uniform and dipolar magnetic field configurations and calculate the orbital velocity of the particles. We assume that the flares observed around supermassive black hole Sagittarius (Sgr) A* detected by the GRAVITY ESO collaboration (on May 27, July 22, and July 28, 2018) are magnetized compact objects, in particular, neutron stars (NSs) and white dwarfs (WDs). Also, we apply orbital and luminosity data from (three) flares to explore the possible role of magnetic interaction on hot spots’ dynamics. First, we found the mass range of SgrA* using the orbital data in the absence of external magnetic fields as M=(3−6.3)M⊙. It is also found that, for magnetized particles that can be in the hot spot’s orbits, the magnetic coupling parameter β has to take values less than 0.13 and 0.25 in the cases of external dipolar and uniform magnetic fields, respectively. The critical values for the surface magnetic fields, mass, and radius of magnetized NSs and WDs are found to be candidates for the hot-spot objects. Finally, we found upper and lower limits for the surface magnetic field, radius, and rotating period of the NSs and WDs, using the luminosity data of the hot spots.

Isotopic enrichment in lanthanide coordination complexes: contribution to single-molecule magnets and spin qudit insights.

Lanthanide Single-Molecule Magnets (SMMs) fascinate the scientific community due to their plethora of potential applications ranging from data storage to spintronic devices and quantum computing. This review article proposes a comprehensive description of the influence of the nuclear spin, i.e. hyperfine interaction, on the magnetic properties of lanthanide SMMs and on quantum information processing of qudit. This influence is analysed for non-Kramers and Kramers lanthanide SMMs as well as for the electronic distribution of the electron in 4f orbitals i.e. oblate and prolate ions. Then the role of magnetic interactions in isotopically enriched polynuclear Dy(III) SMMs is discussed. Finally the possible effect of superhyperfine interaction due to the nuclear spin of elements originating from the surrounding of the lanthanide centre is analyzed. The effect of nuclear spin on the dynamics of the lanthanide SMMs is demonstrated using different techniques such as magnetometry, muon spectroscopy (μ-SR), and Mössbauer and Resonance Vibrational Spectroscopies.

The Role of Magnetic Interaction on the Thermoelectric Performance of ZrNiSn Half‐Heusler Alloys

The half‐Heusler (HH)‐based materials are appealing for mid‐high temperature thermoelectric (TE) applications. Herein, the effect of Mn doping on the TE properties of ZrNiSn HH alloy is explored. The samples of ZrNi1−xMnxSn (x = 0.01–0.03) are prepared via the fast‐processing route comprising arc melting along with spark plasma sintering and then characterized for structural as well as TE properties. The Seebeck coefficient at room temperature with Mn doping is realized to be increased as a result of increased carrier effective mass, which might be due to the charge carrier–magnetic moment interaction. The improved power factor of ≈3.8 × 10−3 Wm−1 K−2 at ≈873 K is noticed for the composition ZrNi0.97Mn0.03Sn. The figure of merit is observed to be more or less unaltered with Mn concentration due to the simultaneously increased thermal conductivity.

Magnetization reversal and microstructure in polycrystalline Fe50Pd50 dot arrays by self-assembling of polystyrene nanospheres

Nanoscale magnetic materials are the basis of emerging technologies to develop novel magnetoelectronic devices. Self-assembly of polystyrene nanospheres is here used to generate 2D hexagonal dot arrays on Fe50Pd50 thin films. This simple technique allows a wide-area patterning of a magnetic thin film. The role of disorder on functional magnetic properties with respect to conventional lithographic techniques is studied. Structural and magnetic characteristics have been investigated in arrays having different geometry (i.e. dot diameters, inter-dot distances and thickness). The interplay among microstructure and magnetization reversal is discussed. Magnetic measurements reveal a vortex domain configuration in all as-prepared films. The original domain structure changes drastically upon thermal annealing performed to promote the transformation of disordered A1 phase into the ordered, tetragonal L10 phase. First-order reversal magnetization curves have been measured to rule out the role of magnetic interaction among crystalline phases characterized by different magnetic coercivity.

Role of magnetic interactions in neutron stars

In this work, we present a calculation of the non-Fermi liquid correction to the specific heat of magnetized degenerate quark matter present at the core of the neutron star. The role of non-Fermi liquid corrections to the neutrino emissivity has been calculated beyond leading order. We extend our result to the evaluation of the pulsar kick velocity and cooling of the star due to such anomalous corrections and present a comparison with the simple Fermi liquid case.

Role of magnetic interactions in neutron stars

In this work, we present a calculation of the non-Fermi liquid correction to the specific heat of magnetized degenerate quark matter present at the core of the neutron star. The role of non-Fermi liquid corrections to the neutrino emissivity has been calculated beyond leading order. We extend our result to the evaluation of the pulsar kick velocity and cooling of the star due to such anomalous corrections and present a comparison with the simple Fermi liquid case.

The role of magnetic interactions in exchange bias properties of MnFe2O4@γ-Fe2O3 core/shell nanoparticles

Low-temperature magnetic properties of assemblies of 3.3 nm sized nanoparticles (NPs) based on a MnFe2O4 core protected by a maghemite shell are investigated. These NPs are obtained by a chemical core/shell method developed for the synthesis of the electrostatically stabilized ferrofluid colloidal dispersions that we probe here. They are model systems where the interparticle interaction is tuned by the NP volume fractions, ranging here between 0.4% and 13.9%. It has been shown that these NPs consist of a well-ordered ferrimagnetic core surrounded by a disordered spin glass-like surface layer and that they display uniaxial magnetic anisotropy. We compare the magnetic hysteresis loops of non-textured frozen dispersions (with magnetic anisotropy axis of NPs distributed at random) with those of a powder based on the same NPs. After cooling under field the hysteresis loops shift along the H axis, expressing the coupling between the spin-ordered cores and the disordered surface layers. The negative H-shift provides an evaluation for the exchange bias (EB) field. The EB field is optimum for a cooling field of the order of the anisotropy field. A comparison between frozen dispersions and disordered powder allows us to distinguish the influence of intra- and interparticle interactions on the EB. Interparticle collective effects dominate in the powder while an intraparticle EB, eventually hindered by dipolar interactions at large volume fraction, is observed in frozen dispersions.

The role of magnetic interactions in natural systems

The role of magnetic interactions in natural systems

Role of Magnetic Interaction in Dense Plasma

Quasiparticle excitations and associated phenomena of energy and momentum transfer rates have been calculated in terms of the drag and the diffusion coefficients exposing clearly the dominance of the magnetic interaction over its electric counterpart. The results have been compared with the finite temperature results highlighting the similarities and dissimilarities in the two extreme regimes of temperature and density. Non-Fermi-liquid behavior of various physical quantities like neutrino mean free path and thermal relaxation time due to the inclusion of magnetic interaction has clearly been revealed. All the results presented in the current review are pertinent to the degenerate and ultradegenerate plasma.

Orbital Hybridization and Magnetic Coupling of the A-Site Cu Spins in CaCu3B4O12 (B = Ti, Ge, and Sn) Perovskites

X-ray absorption spectroscopy (XAS) spectra near the O K-edge of A-site-ordered perovskite with A-site Cu(2+) (S = (1)/(2)) spins were measured. The spectra of ferromagnetic CaCu(3)Ge(4)O(12) and CaCu(3)Sn(4)O(12) showed hybridization between Cu 3d and O 2p orbitals, but magnetic circular dichroism measurement revealed that the O 2p orbital played a less important role in magnetic interaction. The XAS spectra of antiferromagnetic CaCu(3)Ti(4)O(12), on the other hand, showed strong hybridization of the Cu 3d, Ti 3d, and O 2p orbitals. These results demonstrated that direct exchange interaction of the Cu(2+) spins primarily determined the ferromagnetic ordering of CaCu(3)Ge(4)O(12) and CaCu(3)Sn(4)O(12), whereas the involvement of Ti 3d orbitals induced the antiferromagnetic property in CaCu(3)Ti(4)O(12).

Temperature dependence of magnetic properties in Fe/Fe–O nanoparticles dispersed in water

Commercial water dispersions of Fe/Fe–O nanoparticles (∼50–80 nm diameter) were prepared bare and treated with a biodegradable polymer to stabilize the suspension. Hysteresis loops and FC–ZFC curves of samples in liquid and dried form were measured by means of a vibrating sample magnetometer from 77 to 300 K. A marked dependence on the conditioning field is observed in all samples that display the Verwey transition at about 120 K. The role of magnetic interactions on dried samples was also investigated by means of magnetoresistance measurements as a function of temperature.

Competing magnetic interactions in nickel ferrite nanoparticle clusters: Role of magnetic interactions

The magnetic behavior of nickel ferrite nanoparticles of different sizes was studied by annealing nickel ferrite powders at temperatures ranging from 300 to 900 °C. Transmission electron microscopy studies show that the average particle sizes change from ∼8 to ∼120 nm with increasing annealing temperatures. The x-ray diffraction patterns of the annealed samples reveal that a single phase is retained. Hysteresis measurements performed up to a field of 10 kOe show a tendency toward saturation. The saturation magnetization is found to increase with annealing temperature (particle size) with the magnetization tending toward the bulk value for powders annealed at 900 °C. Zero field cooled–field cooled measurements performed at 0.5 kOe indicate the presence of a superparamagnetic phase up to an annealing temperature of 700 °C with blocking temperatures in the range of 150–330 K. Numerical simulations are carried out using an interacting model of an array of single domain magnetic particles to explain the change in the magnetic behavior of the samples with annealing temperature and to estimate the anisotropy of the system. Our studies indicate that the observed magnetic behavior can be explained by the changes in the anisotropy of the system and the dominance of the short range interparticle exchange interactions over the long range dipolar interactions with increasing particle sizes. This change in the interaction profile is further confirmed by the Henkel plots for the particles annealed at different temperatures.

Magnetic interaction induced by the anomaly in kaon-photoproductions

We study the role of magnetic interaction in the photoproduction of the kaon and hyperon. We find that the inclusion of a higher order diagram induced by the Wess–Zumino–Witten term has a significant contribution to the magnetic amplitude, which is compatible to the observed photon asymmetry in the forward angle region. This enables us to use the K∗ coupling constants which have been determined in a microscopic way rather than the phenomenological ones which differ largely from the microscopic ones.

Vortex state and effect of anisotropy in sub-100-nm magnetic nanodots

Magnetic properties of Fe nanodots are simulated using a scaling technique and Monte Carlo method, in good agreement with experimental results. For the 20-nm-thick dots with diameters larger than 60nm, the magnetization reversal via vortex state is observed. The role of magnetic interaction between dots in arrays in the reversal process is studied as a function of nanometric center-to-center distance. When this distance is more than twice the dot diameter, the interaction can be neglected and the magnetic properties of the entire array are determined by the magnetic configuration of the individual dots. The effect of crystalline anisotropy on the vortex state is investigated. For arrays of noninteracting dots, the anisotropy strongly affects the vortex nucleation field and coercivity, and only slightly affects the vortex annihilation field.

Theoretical Studies on the Magnetic Switching Controlled by Stacking Patterns of Bis(maleonitriledithiolato) Nickelate(III) Dimers

Magnetic switchable maleonitriledithiolate (mnt) complexes were studied by density functional theory. The calculations were performed for anion dimers of [RBzPyR'][Ni(mnt)(2)] (RBzPyR' = derivatives of benzylpyridinium) to elucidate magnetostructural correlations and the nature of the weak intermolecular chemical bonding. The calculated results showed that the spin delocalization, favored by the eclipsed stacking and the shorter interlayer distance, was responsible for the diamagnetic character of [1-benzyl-4-aminopyridinium][Ni(mnt)(2)] at low temperature. The weak antiferromagnetic and ferromagnetic interactions were also reproduced for [1-benzyl-4-aminopyridinium][Ni(mnt)(2)] and [1-(4'-fluorobenzyl)pyridinium][Ni(mnt)(2)] at high temperature, respectively. The natural bond orbital analysis suggested that the cooperative effect of the weak intermolecular bondings may be the intrinsic driving force resulting in the switchable property, which is essentially similar to those in organic radicals exhibiting magnetic bistability. Further investigations with varying interlayer distance d, the extent of slippage (slipping distance r and deviation angle alpha), and rotational angle theta suggested that the extent of slippage played an important role in magnetic interactions. Therefore, the abrupt modulation of the extent of slippage in the [Ni(mnt)(2)](-) complexes by external perturbations provided new possibilities for the design of molecular magnetic switching devices.

Spin Densities in Bimetallic Compounds: Polarized Neutron Diffraction

The determination of the spin density map in molecular magnetic compounds provides crucial informations about the phenomena playing a role in magnetic interactions, like spin delocalization and spin polarization. Polarized neutron diffraction on single crystals is the unique experimental technique which allows to visualize the spin distribution over a whole molecule. A review of spin density studies in bimetallic compounds will be presented as well as very recent results obtained on the induced spin density distribution along a ferromagnetic Mn(II)Ni(II) bimetallic chain.

The role of magnetic interactions on the stability of magnetic structures in RCu compounds (R = Ce, Pr and Nd)

We analyze the stability of the magnetic structures of RCu compounds (R = Ce, Pr and Nd), which have been determined by means of neutron diffraction. While CeCu exhibits a simple antiferromagnetic structure with a single propagation vector, NdCu has a complex magnetic behaviour with two propagation vectors. In contrast, no long range magnetic order has been observed in PrCu down to 2 K.

Spin dynamic effects on the resistivity and the magnetoresistance of a La1.85Sr0.15(Cu1−xLix)O4 system with 0.0⩽x⩽0.15

The interplay between hole doping, spin fluctuations, and unusual normal-state properties in layered cuprates is relevant for the physics of high temperature superconductors. For better understanding of the role of magnetic interactions on the conduction mechanism, a systematic study of the normal-state resistivity ρ(x,T) of the La1.85Sr0.15(Cu1−xLix)O4 system with 0.0⩽x⩽0.15 was performed down to 4.2 K. A logarithmic contribution was found to properly describe the ρ(x,T) deviation from linearity as Tc is approached. Scattering of the carriers by spin fluctuations at the Cu–O2 conduction planes is proposed to be the source of the Kondo-like behavior. Negative magnetoresistance measurements up to 8 T, with an increasing intensity with x, confirm the role of spin degrees in the resistivity behavior.

Composition dependence of magnetic properties in amorphous rare-earth-metal-based alloys

Magnetic refrigeration is an emerging new technology for cooling and gas liquefaction. The proper selection of magnetic working materials plays a key role in any design of a magnetic refrigerator. Properly fabricated amorphous rare-earth-metal-based alloys may be promising candidates for magnetic refrigeration applications. Their advantages include tailorable composition, low eddy current and hysteresis losses, improved corrosion resistance, and large specific area. To optimize the composition, bulk magnetic properties of selected Re70M30−xTx (with Re = Gd, Dy, Er, Ho, Tb and M, T = Ni, Fe, Cu, Al) alloys have been investigated in the 5–350 K temperature and 0–7 T DC field range. Far above the magnetic transition, all investigated alloys display a Curie-Weiss behavior consistent with the effective atomic moment of the Re-atoms present. The composition dependence of the Weiss constant reveals that although influenced by the presence of transition metals, the ReRe exchange plays the main role in magnetic interactions. Gd-based alloys display a tendency to form multiple phases, which is supported by the presence of Fe and suppressed by the addition of Al. Single-phase amorphous Re70M30−xTx alloys are characterized by transition temperatures below 200 K, and in spite of their inherently broad transitions, they often display a magnetic entropy change superior or comparable to that of crystalline alloys with similar transition temperatures. Consequently, rare-earth-based amorphous alloys are promising candidates for magnetic refrigeration applications.

Role of magnetic interaction in sediments.

The effect of the magnetic interaction between the magnetic carriers was estimated by a simple pair model, where the remanences of post depositional origin was assumed. The theory predicts a large concentration dependence of the intensity of the remanence for a very low concentration range (packing fraction ≤ 0.1%) if the magnetic particles are small and have a single domain structure. The effect decreases with the increase of the grain size. In order to check the validity of the theory, the intensity of the remanence acquired during the consolidation of artificial sediments was measured as a function of the concentration of fine grain magnetites in a magnetite-talc mixture. The result indicates the large concentration dependence of the remanence intensity. The validity of the various methods, which have been used to normalize the NRM in sediments to obtain the relative intensity change of the earth's magnetic field, was discussed on the basis of the present result.