Exchange Coupling Interaction Research Articles

A study of cation-dependent inverse hydrogen bonds and magnetic exchange-couplings in lanthanacarborane complexes

SummaryTen lanthanacarborane complexes were synthesized to study the rare B−Hδ−∙∙∙Mn+ inverse hydrogen bonds (IHBs). The average bonding energy of B−Hδ−∙∙∙Ln3+ is theoretically determined to be larger than 24 kJ/mol, which is comparable to moderately strong hydrogen bonds (21–56 kJ/mol). In addition to NMR and IR, magnetometer was used to study the exchange-coupling interaction via such B−Hδ−∙∙∙Ln3+ IHBs in detail, and the coupling constant is determined to be −2.0 cm−1, which is strong enough to compare with single-atom bridged dysprosium(III) complexes. Two imidazolin-iminato incorporated complexes have shown energy barrier for magnetization reversal larger than 1000 K, and the exchange-biasing effects are evident. Moreover, the bonding strengths of B−Hδ−∙∙∙Mn+ IHBs are cation-dependent. If M = Na, the B−Hδ−∙∙∙Na+ bonding energy is reduced to 14 kJ/mol, and the dimerization process is no longer reversible. The exchange-biasing effect is also disappeared. We believe such a finding extends our knowledge of IHBs.

Magnetic phase transitions of phosphorene-like nano-structure: Monte Carlo study

ABSTRACT The aim of this paper is to investigate the magnetic properties of phosphorene-like nano-structure applying the Metropolis Monte Carlo simulations. Based on the spin mixed system σ = 7/2 and S = 2, we have analysed the variation of the magnetic phase states in the absence of temperature and the magnetizations of the compound with temperature for the mixed spins phosphorene. We also studied the effect of varying other parameters such as the exchange coupling interactions, the temperature, the external magnetic field and the crystal fields on the total and partial magnetizations. Besides, we have discussed the effect of each parameter on the critical temperature of the system. Finally, we have presented the magnetic hysteresis cycles, for different values of crystal field, exchange coupling interactions and temperature.

A Comparison of Thermal and Magnetic Behaviors in Triangular, Square and Pentagonal Husimi-Like Structures: Monte Carlo Simulations

In this work, Monte Carlo simulations have been performed to investigate the magnetic properties and thermal behavior of different Husimi-like structures: triangular, square and pentagonal. In fact, the Blume-Capel model has been adopted to study such Husimi lattices in the framework of the Ising model spin-1. Furthermore, we have examined the computed blocking temperatures. Also, the behavior of each Husimi geometry has been studied and discussed. Besides, the effects of the magnetization versus the crystal field, the exchange coupling interaction and the external magnetic field have been investigated. Such comparison of triangular, square and pentagonal Husimi-like structures allowed us to deduce interesting properties related to the geometry of each structure.

Tailoring photocatalytic activity and magnetic properties of BiFeO3/CeO2/Bi2Fe4O9 composites

BiFeO3/CeO2/Bi2Fe4O9 (BFO-CF) composite and BiFeO3 nanotube were synthesized via the electrospinning method. The obtained nanotubes were characterized to analyze the structural, optical and magnetic properties. Results of XRD patterns and Rietveld analysis further confirmed the existence of multiple phases in BFO-CF composite, which plays an important role in terms of enhanced photocatalytic and magnetic properties. The selected area electron diffraction (SAED) pattern demonstrated single-crystalline structure of pure BiFeO3 nanotube and polycrystalline phases of BFO-CF composite. It was found that BFO-CF composite with an average diameter of 79.4 nm showed size effect, which enhanced the photocatalysis and magnetism. Magnetic measurements at 300 K exhibited higher values of remanent magnetization and coercivity in BFO-CF composites. The results of switching field distribution (SFD) measurement in BFO-CF composite at 300 K exhibited higher values of double peak than corresponding values at 10 K, which indicated lower temperature can inhibit magnetic reversal and weaken exchange coupling interaction between hard and soft phase. UV–vis spectrum measurements showed excellent visible light response, with a slight red shift occurring in the cut-off wavelength of BFO-CF composite. The measurement results suggested formation of BFO-CF composite, that induce higher separation efficiency of e−/h+ pairs, thus enhancing photocatalytic properties than that of BFO nanotube, which could be a suitable candidate in the photocatalytic degradation of organic pollutants.

Structural and magnetic properties of hard-soft BaFe12O19/(Zn0.5Co0.5)Fe2O4 ferrites

Hard-soft nanocomposites of (1 − x) BaFe12O19/x(Zn0.5Co0.5)Fe2O4, for x = 0.00, 0.25, 0.50, 0.75 and 1.00, were prepared via co-precipitation and high-speed ball milling techniques, respectively. The synthesized samples were characterized via x-ray diffraction, transmission electron microscope, Fourier transform infrared (FTIR), and vibrating sample magnetometer. XRD revealed the formation of hard-soft nanocomposites. TEM indicated that the two phases are well distributed and the particle size distribution is narrower for low content of soft phase, leading to better exchange coupling between the grains. Magnetic measurements were performed at 300 K and 77 K. The results showed a good single-phase magnetic behavior, verifying the good exchange coupling between hard and soft phases. For low (Zn0.5Co0.5)Fe2O4 content, the dipolar interactions were dominated by the exchange-coupling interactions. Additionally, the optimum values of saturation and remanent magnetizations, coercivity, and squareness ratio were obtained for x = 0.5. This was attributed to the dominance of exchange-coupling interaction. The enhancement of magnetic properties and energy product (BH)max for nanocomposites at low temperature is skilled in the reduction of the thermal fluxes of magnetic moments at the surface. The maximum energy product (BH)max was observed in C2 at both temperatures with a smaller value than that of pure BaFe12O19.

Effect of grain and phase boundaries on soft magnetic properties of FeCoNiAlSi high-entropy alloys

The impact of grain and phase boundaries on the magnetic domain structure and soft magnetic properties of the FeCoNi(AlSi)x (0.1 ≤ x ≤ 0.7) high-entropy alloys (HEAs) have been studied in this work. The x = 0.1 alloy with single FCC phase and the x = 0.5 alloy with single BCC phase show obvious grain and phase boundaries, while the x = 0.3 containing FCC plus BCC phase and x = 0.7 alloy containing single BCC phase only present phase boundaries. Besides, The magnetic domains can cross grain and phase boundaries when the exchange coupling interaction is stronger enough. However, the domains are blocked for x = 0.5 alloy due to the strong pinning effect of grain boundaries (GBs). Moreover, the x = 0.1 and x = 0.5 alloys display good statically soft magnetic properties with relatively low coervivity (Hc) and high maximum permeability (μmax), whereas the x = 0.3 and x = 0.7 alloys exhibit good dynamic magnetic parameters with low alternating current (AC) Hc and total loss (Ps).

Ferromagnetic evolution in Nd3+, Ti4+ co-doped antiferromagnetic YFeO3

The structure-property correlation in polycrystalline powders of Y1-xNdxFe1-(4/3)yTiyO3 (x = 0.05, 0.10, 0.15; y = 0.05) was investigated. Diffuse reflectance spectra analysis revealed a reduction in the bandgap from 2.14 to 1.92 eV on increasing x. The remnant magnetization (Mr) and coercivity (Hc) increased from 0.145 to 7.50 emu/g and 0.099–8.46 kOe, respectively. The infusion of Nd3+ at Y3+ and Ti4+ at Fe3+ sites suggested that the magnetic behavior of the chosen composition of Y1-xNdxFe1-(4/3)yTiyO3 tilts away from the G-type anti-ferromagnetism. The magnetic orientation is achieved largely due to the Fe3+- O2− - Fe3+, Fe4+- O2− - Fe4+ super-exchange coupling, and Fe3+- O2− - Fe4+ double exchange coupling interactions. These materials in the present study with the enhanced magnetic and optical properties thus exhibit potential for varied applications.

Origin of the magnetic properties of MnFe2O4 spinel ferrite: Ab initio and Monte Carlo simulation

In this work, the electronic and magnetic properties of bulk spinel ferrite MnFe2O4 were carried out using ab initio calculations and Monte Carlo simulation. The electronic properties as well as, the exchange coupling interactions and the magnetic anisotropy were calculated using Density functional theory. The obtained exchange couplings between nearest n eighbours (JAB = −21.8 K, JBB = 13.7 K and JAA = 8.6 K) and the magnetic anisotropy were used as input parameters in a classical Ising model to study the finite-temperature effects on the magnetic properties of bulk MnFe2O4 with different size. It is shown that MnFe2O4 has a magnetic transition around 559.26 K.

Memory and superposition in a superspin glass

The non-equilibrium dynamics of the superspin glass state of a dense assembly of ~ 2 nm MnFe2O4 nanoparticles was investigated by means of magnetization, ac susceptibility and Mössbauer spectroscopy measurements and compared to the results of Monte Carlo simulations for a mesoscopic model that includes particles morphology and interparticle interactions. The zero-field cooled (ZFC), thermoremanent (TRM), and isothermal remanent magnetization (IRM) were recorded after specific cooling protocols and compared to those of archetypal spin glasses and their dimensionality. The system is found to display glassy magnetic features. We illustrate in detail, by a number of experiments, the dynamical properties of the low-temperature superspin glass phase. We observe that these glassy features are quite similar to those of atomic spin glasses. Some differences are observed, and interestingly, the non-atomic nature of the superspin glass is also reflected by an observed superspin dimensionality crossover. Monte Carlo simulations—that explicitly take into account core and surface contributions to the magnetic properties of these ultrasmall nanoparticles in direct contact, as well as interparticle interactions—evidence effects of the interplay between (intraparticle) core/surface exchange coupling and (interparticle) dipolar and exchange interactions.

Room temperature superconductivity dome at a Fano resonance in superlattices of wires

Recently room temperature superconductivity with degrees Celsius has been discovered in a pressurized complex ternary hydride, CSH x , which is a carbon- and hydrogen-doped H3S alloy. The nanoscale structure of H3S is a particular realization of the 1993 patent claim of superlattice of quantum wires for room temperature superconductors and the maximum T C occurs at the top of a superconducting dome. Here we focus on the electronic structure of materials showing nanoscale heterostructures at the atomic limit made of a superlattice of quantum wires like hole-doped cuprate perovskites, and organics focusing on A15 intermetallics and pressurized hydrides. We provide a perspective of the theory of room temperature multigap superconductivity in heterogeneous materials tuned at a shape resonance or Fano resonance in the superconducting gaps near a Lifshitz transition focusing on H3S where the maximum T C occurs where the multiband metal is tuned by pressure near a Lifshitz transition. Here the superconductivity dome of T C vs. pressure is driven by both electron-phonon coupling and contact exchange interaction. We show that the T C amplification up to room temperature is driven by the Fano resonance between a superconducting gap in the anti-adiabatic regime and other gaps in the adiabatic regime. In these cases the T C amplification via contact exchange interaction is the missing term in conventional multiband BCS and anisotropic Migdal-Eliashberg theories including only Cooper pairing.

Blume-Capel model of a borophene layers structure with RKKY interactions: Monte Carlo simulations

In this paper, we study the magnetic properties of a bi-layer borophene structure with RKKY (Ruderman-Kittel-Kasuya-Yoshida) interactions. The system is composed by two magnetic layers with mixed spins σ = ±3/2, ±1/2 and S = 0, ±1, separated by (L) non-magnetic planes. Firstly, for zero temperature, the ground state phase diagrams are reported and discussed. Secondly, we use the Monte Carlo simulations to explore the RKKY interactions effect on the magnetic properties of the system. The transition temperature increases when decreasing the number (L) of nonmagnetic layers. Also, the effect of the exchange coupling interactions on the transition temperature behavior is studied. Finally, we report the effect of different physical parameters on the magnetic hysteresis cycles.

Exchange coupling and dipolar interactions in FINEMET/Fe50Pd50 composites ribbons

Asymmetrical giant magnetoimpedance (AGMI) effect was investigated in FINEMET/Fe50Pd50 composite ribbons. Composite ribbon samples of 33 μm-thickness FINEMET sputtered with a layer of Fe50Pd50 film were produced, and the microstructure and magnetic properties were investigated. The results showed that the MI response was enhanced by Fe50Pd50 coating layer. The Fe50Pd50 coating layer generates a bias field to FINEMET ribbon, which leads to the asymmetry of GMI curves. The bias field decreases with the increasing of the thickness (t) of Fe50Pd50 coating layer. The asymmetry of GMI curves almost disappears at t = 70 nm. Asymmetry could be tuned by changing the thickness of Fe50Pd50 coating layer, which is analyzed in terms of exchange coupling and dipole–dipole interaction between FINEMET ribbon and Fe50Pd50 layer. The high sensitivity of GMI was used to separate the two interactions for the first time. The results opened the possibilities for application of FINEMET/Fe50Pd50 composite ribbons in linear magnetic field sensors.

Ferrielectric properties of a bilayer structure with RKKY-like interaction: A Monte Carlo study

The ferrielectric properties of a bilayer structure separate by electrical insulating layers, with RKKY interactions in the Blume–Capel model. The system is composed of two interacting A (spin S=5∕2) and B (spin σ=2) planes in which the intralayer couplings are ferroelectric while the interlayer interactions are antiferroelectric. The temperature dependence of the ferroelectricity of a bilayer structure separate by electrical insulating layers, with RKKY interactions in the Blume–Capel model has been investigated. The effects of external longitudinal electric (EZ) and crystal anisotropy DA and DB fields have been investigated. On the other hand, the variation of total and partial polarizations with exchange coupling interactions JA, JB, JRKKY, crystal and external longitudinal electric fields was discussed. Finally, the influence of the exchange interactions and crystal field on the critical temperatures of the system and hysteresis cycles has been examined.

Structure and Magnetic Properties of Melilite-Type Compounds RE2Be2GeO7 (RE = Pr, Nd, Gd-Yb) with Rare-Earth Ions on Shastry-Sutherland Lattice.

Rare-earth (RE)-based frustrated magnets, such as typical systems of combining strong spin-orbit coupling (SOC), geometric frustration, and anisotropic exchange interaction, can give rise to diverse exotic magnetic ground states such as quantum spin liquid. The discovery of new RE-based frustrated materials is crucial for exploring the exotic magnetic phases. Herein, we report the synthesis, structure, and magnetic properties of a family of melilite-type RE2Be2GeO7 (RE = Pr, Nd, and Gd-Yb) compounds crystallized in a tetragonal P4̅21m structure, where magnetic RE3+ ions lay out on the Shastry-Sutherland lattice (SSL) within the ab plane and are well separated by nonmagnetic [GeBe2O7]6- polyhedrons along the c-axis. Temperature (T)-dependent susceptibilities χ(T) and isothermal magnetization M(H) measurements reveal that most RE2Be2GeO7 compounds except RE = Tb show no magnetic ordering down to 2 K despite the dominant antiferromagnetic (AFM) interactions, where Tb2Be2GeO7 undergoes AFM transition with Néel temperature TN ∼ 2.5 K and field-induced spin flop behaviors (T < TN). In addition, the calculated magnetic entropy change ΔSm from the isothermal M(H) curves reveals viable magnetocaloric effect for RE2Be2GeO7 (RE = Gd and Dy) in liquid helium temperature regimes; Gd2Be2GeO7 shows the maximum ΔSm up to 54.8 J K-1 kg-1 at ΔH = 7 T and Dy2Be2GeO7 has the largest value ΔSm = 16.1 J K-1 kg-1 at ΔH = 2 T in this family. More excitingly, the rich diversity of RE ions in this family enables an archetype for exploring exotic quantum magnetic phenomena with large variability of spin located on the SSL lattice.

Exchange spring behaviour in BaFe12O19/CoFe2O4 magnetic nanocomposites

Abstract In this work, nanopowders of BaFe12O19 and CoFe2O4 and nanocomposites of (1−x) BaFe12O19/xCoFe2O4, for x = 0.00, 0.25, 0.50, 0.75 and 1.00, were prepared via co-precipitation and high-speed ball milling techniques, respectively. For structural analysis, the X-ray diffraction revealed the formation of hexagonal BaFe12O19 and spinel CoFe2O4 ferrites, and the average crystallite sizes were about 35 nm and 15 nm, respectively. The transmission electron microscope indicated that the two phases are well distributed and the grain sizes of the composite powders are verified employing the size distribution histograms where two peaks were obtained separately for both ferrites. From EDX spectra, it was shown that all samples exhibit an excellent compositional homogeneity verifying the presence of both phases in the obtained nanocomposite powders. Magnetic measurements were performed via a vibrating sample magnetometer at 300 K and 77 K. The results showed a good single-phase magnetic behavior, proving the good exchange coupling between hard and soft phases. For low CoFe2O4 content, the dipolar interactions were dominated by the exchange-coupling interactions. Additionally, the optimum values of saturation and remanent magnetizations as well as the squareness ratio were obtained for the x = 0.5. This was attributed to the dominance of exchange-coupling interaction. Magnetic properties for nanocomposites were improved as the temperature falls from room temperature down to 77 K. This increase is skilled to the reduction in the thermal fluxes of magnetic moments at the surface.

Magnetic Properties and Compensation Temperature in Tri-layer Graphyne-Like Structure: Monte Carlo Simulations

In this paper, we study the magnetic properties of a tri-layer graphyne-like structure using Blume-Capel Ising model. The studied system is composed by a mixed spins σ = ± 5/2, ± 3/2 and ± 1/2 (in the plane B) and S = ± 2, ± 1 and 0 (in the plane A). The study is performed through Monte Carlo simulations under the Metropolis algorithm. Besides, we examine the effects of the exchange coupling interactions on the obtained compensation temperature. Additionally, we investigate the effects of the crystal and external magnetic fields on the partial and total magnetizations. The magnetic and thermal properties of the considerate system are largely affected by the exchange coupling interactions, the crystal and external magnetic fields.

Magnetic Properties of the Nano Brownmillerite KBiFe2O5: Monte Carlo Simulations

In this paper, we have used the Monte Carlo simulations (MCSs) to investigate the magnetic properties of the brownmillerite KBiFe2O5 (KBFO) compound. The different exchange coupling interactions [Formula: see text], [Formula: see text] and [Formula: see text] between different irons Fe atom have been outlined including the angles between Fe1-O-Fe2. The double exchange interaction is caused by the existence of the oxygen atoms. In a first step, we present the ground state phase diagrams in the absence of any temperature fluctuations, in different physical parameter planes. Then we present investigation of the magnetic properties and the behavior of the total magnetizations, the total susceptibilities, as a function of temperature, crystal field, the exchange coupling interactions and the external magnetic field. Also, we provide the dependency of the total magnetizations showing the hysteresis loops of the KBFO compound, for selected values of temperature, crystal field and the exchange coupling interactions.

Magnetic and transport properties of orthorhombic rare-earth aluminum germanide GdAlGe

The structure, magnetic and transport properties of the orthorhombic rare-earth aluminum germanide GdAlGe are systematically studied using X-ray diffraction, scanning electron microscopy (SEM), magnetic and electric measurements. A phase transition from tetragonal to orthorhombic structure occurs at 1204 K. Orthorhombic GdAlGe, which crystallizes in YAlGe-type structure (Cmcm, N 63, oS12) with lattice parameters a = 4.0605 Å, b = 10.5183 Å and c = 5.8001 Å, consists of two kinds of Al-Ge clusters and the slanted Gd3 isosceles triangles Δ and reversal ∇ with inversion symmetry. GdAlGe orders antiferromagnetically with a Néel temperature of 34 K, it might be due to the exchange coupling interaction of slanted magnetic isosceles triangles Gd3 △↑ and reversal Gd3 ∇↓. Magnetic transport is relative to the magnetic scattering between spins of the conduction electrons and magnetic excitations. The positive magnetoresistance MR with a maximum of 23% is obtained, this phenomenon might be due to disorderedly magnetic scattering during the magnetizing process.

Ground state and critical behavior of a core/shell kekulene-like structure by Monte Carlo study

In this paper, we inspect the magnetic properties of a core/shell Kekulene-like structure consisting of mixed spins (σ = 2; S = 1), by means of Monte Carlo simulations. Firstly, we carry out an analysis of the ground state phase diagrams to determine all probable and stable configurations depending on the minimization of the energies of the system. Furthermore, the magnetizations and susceptibilities as a function of temperature are obtained with the effect of the crystal field and the exchange coupling interactions of the system. To conclude, we discuss the hysteresis loops as a function of the external magnetic field.

Origin of Magnetic Relaxation Barriers in a Family of Cobalt(II)-Radical Single-Chain Magnets: Density Functional Theory and Ab Initio Calculations.

Density functional theory (DFT) and ab initio calculations were performed to probe the origin of the magnetic relaxation barriers for two finite single-chain magnets (SCMs) featuring a one-dimension chain, Co(hfac)2(R-NapNIT) (R-NapNIT = 2-(2'-(R-)naphthyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, R = MeO (1) or EtO (2)). Our calculations show that the strong intrachain CoII-CoII exchange coupling interactions transmitted by radicals can contribute much more than ionic anisotropy to the height of the reversal barrier of magnetization for the single-chain magnets (SCMs) with |2E| < |4J/3|. In addition, the anisotropic energy barrier ΔA decreases with the decrease of |2E/J| ratio and finally vanishes in the limit of broad domain walls (|2E| < < |4 J/3|). Therefore, the total magnetic relaxation energy barriers of two SCMs mostly originate from the correlation energy barrier Δξ deriving from the indirect ferromagnetic interaction between CoII-CoII transmitted by the strong CoII-radical antiferromagnetic interactions.