Types Of Exchange Interactions Research Articles

Utilization of Aloe vera-infused Sm3+ doped La2MoO6 nanophosphors: Their role in anti-counterfeiting, white LEDs and transport properties

In the realm of anti-counterfeiting (AC) measures, the focus has increasingly turned towards fluorescent inks, appreciated for their practicality and environmentally friendly nature. However, their susceptibility to wear and vulnerability to moisture damage has hindered their widespread application. Additionally, most available fluorescent inks are single-colored, toxic, and skin-irritating, making them ill-suited for real-world use. In light of these challenges, this article delves into the impact of introducing Sm3+ ions into the La2MoO6 host lattice. The green solution combustion method is employed to synthesis 1–11 mol % Sm3+ doped La2MoO6:Sm3+ nanophosphors (LMO:Sm3+ (1–11 mol %) NPs. The effects of rare earth doping are examined through X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and photoluminescence (PL) analysis. The PL spectra reveal four emission bands, with a prominent 603 nm wavelength band emitting an orange-red hue attributed to the electronic transition of Sm3+ ions. Notably, the impact of Sm3+ ion doping on the phosphor’s luminescence spectra is prominently featured. The optimal concentration is found to be 5 mol % (LMO:5Sm3+), with concentration quenching primarily attributed to exchange-type interactions. The luminescent properties are evidenced by Commission Internationale de l’éclairage (CIE) color coordinates (0.6063, 0.3901), color purity (CP = 99.10 %), and correlated color temperature (CCT = 1383 K). Furthermore, the study delves into optical parameters such as energy band gap and refractive index, revealing values of 2.313 and 2.252 eV, respectively, for the optimal molar concentration. These findings hold promise in the development of AC inks suitable for screen-printing and writing on a variety of surfaces. The resultant patterns exhibit vivid orange-red fluorescence under UV 365 nm irradiation, showcasing potential applications in encryption, security marking, and optical authentication.

Superexchange and spin-orbit coupling in monolayer and bilayer chromium trihalides

We build a microscopic model to study the intra- and inter-layer superexchange due to electrons hopping in chromium trihalides ($\mathrm{CrX}_3$, X= Cl, Br, and I). In evaluating the superexchange, we identify the relevant intermediate excitations in the hopping. In our study, we find that the intermediate hole-pairs excitations in the $p$-orbitals on X ion play a crucial role in mediating various types of exchange interactions. In particular, the inter-layer antiferromagnetic exchange may be realized by the hole-pair-mediated superexchange. Interestingly, we also find that these virtual hopping processes compete with each other leading to weak intra-layer ferromagnetic exchange. In addition, we also study the spin-orbit coupling effects on the superexchange and investigate the Dzyaloshinskii-Moriya interaction. Finally, we extract the microscopic model parameters from density functional theory for analyzing the exchange interactions in a monolayer $\mathrm{CrI}_3$.

Giant effective g factor and anisotropy in Sn1−xEuxTe: Contribution from spin-orbit and s/p − f hybridization

We consider the effective equation of motion starting from the fundamental six-level double group basis as stated by Mitchell-Wallis under effective mass representation in the presence of spin-orbit interaction, external magnetic field, and impurity. Here, the hybridized exchange type interactions due to magnetic impurities with carrier and external magnetic field are incorporated in the k⃗⋅π⃗ perturbation technique. Finally, we perform a systematic analysis of the effective g factor and its anisotropy in Sn1−xEuxTe as functions of carrier concentration and impurity at T = 300 K. We report very high values of effective g factor; g = 1028 for n − Sn1−xEuxTe and g = 997 for p − Sn1−xEuxTe with large anisotropies around x = 0.02 as compared to Pb1−xEuxTe in the concentration range 0.01 × 1019cm−3 to 0.1 × 1019cm−3. Our calculated results and trends are very similar to others’ work, previously reported for similar systems. The presence of a large effective g factor renders this material a potential choice for spintronics applications.

First-principles study of magnetic properties of the cobalt doped silver copper sulfide

First principles calculations in the framework of density functional theory have been carried out to study the electronic and magnetic properties of cobalt (Co) doped silver copper sulfide (AgCuS) system. Cobalt doped at Cu site can induces a significant amount of magnetism in AgCuS. The total and partial density of states reveal that 3d orbital electron of the Co atom is the primary source of magnetism and the rest of magnetic moment comes from the 3d orbital electron of Cu atoms. Spin-spin interaction study suggests a ferromagnetic ordering with Ruderman-Kittel-Kasuya-Yoshida (RKKY) type of exchange interaction. The spin polarized density of states calculation suggest the presence of polarized density of states at the Fermi level which makes the system more interesting as a half-metallic ferromagnetic system.

Tuning of Cr-Cr Magnetic Exchange through Chalcogenide Linkers in Cr2 Molecular Dimers.

A set of three Cr-dimer compounds, Cr2Q2(en)4X2 (Q: S, Se; X: Br, Cl; en: ethylenediamine), with monoatomic chalcogenide bridges have been synthesized via a single-step solvothermal route. Chalcogenide linkers mediate magnetic exchange between Cr3+ centers, while bidentate ethylenediamine ligands complete the distorted octahedral coordination of Cr centers. Unlike the compounds previously reported, none of the chalcogenide atoms are connected to extra ligands. Magnetic susceptibility studies indicate antiferromagnetic coupling between Cr3+ centers, which are moderate in Cr2Se2(en)4X2 and stronger in Cr2S2(en)4Cl2. Fitting the magnetic data requires a biquadratic exchange term. High-frequency EPR spectra showing characteristic signals due to coupled S = 1 spin states could be interpreted in terms of the "giant spin" Hamiltonian. A fourth compound, Cr2Se8(en)4, has a single diatomic Se bridge connecting the two Cr3+ centers and shows weak ferromagnetic exchange interactions. This work demonstrates the tunability in strength and type of exchange interactions between metal centers by manipulating the interatomic distances and number of bridging chalcogenide linkers.

Multiferroic properties of GdFe0.9M0.1O3 (M\u2009=\u2009Ag1+, Co2+ and Cr3+) nanoparticles and evaluation of their antibacterial activity

Multifunctional nanoparticles NPs with material composition GdFe0.9M0.1O3; M = Ag, Co, and Cr have successfully been synthesized using the citrate auto-combustion technique. The single phase of the orthorhombic perovskite structure is ratified from the XRD data. The structural, magnetic, and thermoelectric power of the samples along with the results of antibacterial activities are reported in the present manuscript. The variation in the magnetization is argued in view of the strength and type of exchange interaction as well as buckling of the < BO6 > octahedron. The super exchange interaction between the Fe–O–Fe and the Cr–O–Cr and the randomness of Cr ions in the host lattice site are the main reasons behind the weak ferromagnetism obtained from GdFe0.9Cr0.1O3. Ferroelectricity and antiferromagnetism have a dissimilar origin and appear independently. The origin of antiferromagnetism is the spin canting of the B ions. However, the origin of the ferroelectric properties is the hybridization between B cations and O2− anion. The use of silver metal particles as antibacterial agents is noteworthy due to their advantages in terms of chemical stability, efficacy and long-term durability. These advantages can be extended by considering the relatively low toxicity of these particles to the human body compared to other inorganic metals.

Ultrahigh-performance supercritical fluid chromatography – mass spectrometry for the qualitative analysis of metabolites covering a large polarity range

The applicability of ultrahigh-performance supercritical fluid chromatography coupled with mass spectrometry (UHPSFC/MS) for the qualitative analysis of metabolites with a wide polarity range (log P: −3.89–18.95) was evaluated using a representative set of 78 standards belonging to nucleosides, biogenic amines, carbohydrates, amino acids, and lipids. The effects of the gradient shape and the percentage of water (1, 2, and 5%) were investigated on the Viridis BEH column. The screening of eight stationary phases was performed for columns with different interaction sites, such as hydrogen bonding, hydrophobic, π-π, or anionic exchange type interactions. The highest number of compounds (67) of the set studied was detected on the Torus Diol column, which provided a resolution parameter of 39. The DEA column had the second best performance with 58 detected standards and the resolution parameter of 54. The overall performance of other parameters, such as selectivity, peak height, peak area, retention time stability, asymmetry factor, and mass accuracy, led to the selection of the Diol column for the final method. The comparison of additives showed that ammonium acetate gave a superior sensitivity over ammonium formate. Moreover, the influence of the ion source on the ionization efficiency was studied by employing atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI). The results proved the complementarity of both ionization techniques, but also the superior ionization capacity of the ESI source in the negative ion mode, for which 53% of the analytes were detected compared to only 7% for the APCI source. Finally, optimized analytical conditions were applied to the analysis of a pooled human plasma sample. 44 compounds from the preselected set were detected in human plasma using ESI-UHPSFC/MS in MSE mode considering both ionization modes.

Long-distance coupling and energy transfer between exciton states in magnetically controlled microcavities

Coupling of quantum emitters in a semiconductor relies, generally, on short-range dipole-dipole or electronic exchange type interactions. Consistently, energy transfer between exciton states, that is, electron-hole pairs bound by Coulomb interaction, is limited to distances of the order of 10 nm. Here, we demonstrate polariton-mediated coupling and energy transfer between excitonic states over a distance exceeding 2 μm. We accomplish this by coupling quantum well-confined excitons through the delocalized mode of two coupled optical microcavities. Use of magnetically doped quantum wells enables us to tune the confined exciton energy by the magnetic field and in this way to control the spatial direction of the transfer. Such controlled, long-distance interaction between coherently coupled quantum emitters opens possibilities of a scalable implementation of quantum networks and quantum simulators based on solid-state, multi-cavity systems.

Exchange Interactions in NiFe/Ta/IrMn Heterostructures under Conditions of Tantalum Deficiency

In the NiFe/Ta/IrMn structures, the contributions of two types of exchange interactions at the NiFe/IrMn interface, partially separated by sections of the nonmagnetic tantalum interlayer, are distinguished. One type of exchange is “contact”—it occurs directly at the NiFe/IrMn interface. Another type is “interlayer,” which takes place through the conduction electrons of the tantalum interlayer. A comparison of the temperature dependences of the exchange bias of the hysteresis loops at fixed parameters of the ferromagnetic layers and various effective thicknesses of the nonmagnetic interlayer made it possible to separate the contributions of the above types of exchange interactions and determine their temperature dependences individually. The exchange interaction energies at the NiFe/IrMn and NiFe/Ta/IrMn interfaces were determined.

Обменные взаимодействия в гетероструктурах NiFe/Ta/IrMn в условиях дефицита Ta

In the NiFe/Ta/IrMn structures, the contributions of two types of exchange interactions are separated at the NiFe/IrMn interface, partially separated by non-magnetic Ta fragments. The first “contact” exchange corresponds to the NiFe/IrMn fragments. The second “interlayer” exchange is provided by the Ta conduction electrons in the NiFe/Ta/IrMn fragments. A comparison of the temperature dependences of the exchange bias in heterostructures with varied Ta spacer at fixed parameters of the ferromagnetic layers allowed us to separate the contributions of the above types of exchange interactions and to establish their temperature dependences. The energies of the exchange interactions in the NiFe/IrMn and NiFe/Ta/IrMn fragments were determined.

Thermodynamic Properties of Heisenberg Spin Systems

We present the simulation results of magnetic 2D and 3D structures with direct (for both of them) and Dzyaloshinskii-Moriya (DMI) (for 2D lattice) interactions in the frame of the Heisenberg model. We have adapted the multipath Metropolis algorithm for systems with complex types of exchange interactions and rough energy landscapes. We show the temperature behavior of magnetization, energy, and heat capacity, and reveal its critical temperatures and order parameter.

Magnetically Active 3d Metal Complexes with 3-Amino-4-Ethoxycarbonylpyrazole

Coordination compounds of iron(II) and nickel(II) with 3-amino-4-ethoxycarbonylpyrazole (L), FeL2A2 (A = Cl– (I), $${{{\text{C}}}_{{\text{2}}}}{\text{N}}_{{\text{3}}}^{-}$$ (II)), [FeL2(NCS)2(H2O)2] (III), and NiL2Br2 (IV), are synthesized. The compounds are studied by X-ray diffraction analysis, IR spectroscopy, and UV spectroscopy (diffuse reflectance spectra). A single crystal is observed for complex III, and its crystal structure is determined by X-ray structure analysis (СIF file CCDC no. 1857220). It is shown that L coordinates to the metal via the monodentate mode by the N(2) atom of the pyrazole cycle. The study of the temperature dependence µeff(Т) in a temperature range of 2–300 K shows exchange interactions of the antiferro- or ferromagnetic character between the M2+ ions in the complexes. The type of exchange interactions depends on the composition of the compound.

Magnetic properties and spin momentum densities of Ni excess Ni-Mn-Sn Heusler alloys

Abstract The role of excess Ni in Ni2+xMn1−xSn (x = 0.05, 0.1) Heusler alloys has been reported using temperature dependent magnetic Compton spectroscopy. The experimental Compton profiles from magnetic electrons have been analyzed to quantify the contribution of Mn 3d electrons, Ni sites and sp-electrons in building-up the total spin moments. The experimentally deduced spin momentum densities, total and element-specific spin moments are examined using theoretical investigations within the spin polarized relativistic Korringa-Kohn-Rostoker method. The build-up of spin moments has been explored in terms of total and projected density of states. Site-dependent Ni magnetic moment is also discussed. Heisenberg exchange coupling parameters are also computed to study the change in Ruderman-Kittel-Kasuya-Yosida type exchange interaction on increasing Ni concentration in the Ni-Mn-Sn system.

Study of electron-phonon coupling and its effect on electrical resistivity in HF systems

In this work, we report on theoretical study of the effect of electron-phonon (EP) interaction in THz frequency and temperature dependence of the electrical resistivity in heavy fermion (HF) systems. For this purpose, a model Hamiltonian is considered which consists of the Heisenberg type exchange interaction between localized moments and a tight binding model called the Kondo lattice model (KLM). The effect of EP coupling on electrical resistivity is presented by considering phonon interaction to bare f-electrons, band electrons and to the hybridization between band and f-electrons as a perturbed term. The phonon Hamiltonian in harmonic approximation is also included. The model Hamiltonian is solved by employing the mean-field theory (MFT) along with the Hubbard model of approximation. The temperature- and frequency-dependent electrical resistivity exhibits change in slopes at T[Formula: see text] as well as at T[Formula: see text]. The theoretical findings from the graphical analysis by varying the model parameters g[Formula: see text], g[Formula: see text] and g[Formula: see text] are compared to some of the experimental results in HF systems.

Pair-delocalization in trigonal mixed-valence clusters: new insight into the vibronic origin of broken-symmetry ground states.

A new vibronic mechanism for the stabilization of pair-delocalized electronic states in trigonal trimeric mixed valence complexes (such as iron-sulfur [Fe3S4]0 proteins) is proposed. Unlike the previously reported mechanism based on the Piepho-Krausz-Schatz model dealing with the local "breathing" vibrations, the present mechanism involves the multicenter vibrations of the triangular complex, which change the metal-metal distances. The former mechanism of the vibronic coupling in combination with the double exchange and Heisenberg type exchange (superexchange) interactions accounts for the existence of the pair-delocalized states of many-electron mixed valence clusters in the intermediate ground spin states. In contrast to the previous model, within which the conditions for the occurrence of pair delocalized states are spin-dependent, the pair delocalization phenomenon in the proposed model is exclusively based on a clear physical mechanism of the interplay between the inter-center vibronic coupling and electron transfer. Therefore, the proposed mechanism demonstrates that the pair delocalization is a more common feature of mixed valence complexes and can appear not only in multi-electron trimers as a result of the interplay between several parameters, but even in one-electron mixed valence trimers in which neither double exchange nor superexchange is operative. The conditions for the pair delocalization in the proposed model are shown to be dependent on the value and sign of the electron transfer parameter as well as on the ratio of the frequencies of the fully symmetric (a1) and doubly degenerate (e) vibrations of a triatomic molecule.

Field-induced quantum magnetism in the verdazyl-based charge-transfer salt[o−MePy−V−(p−Br)2]FeCl4

We successfully synthesized a verdazyl-based charge-transfer salt $[$$o$-MePy-V-($p$-Br)$_2]$FeCl$_4$, which has an $S_{\rm{V}}$=1/2 on the radical $o$-MePy-V-($p$-Br)$_2$ and an $S_{\rm{Fe}}$=5/2 on the FeCl$_4$ anion. $Ab$ $initio$ molecular orbital calculations indicate the formation of an $S_{\rm{V}}$=1/2 honeycomb lattice composed of three types of exchange interaction with two types of inequivalent site. Further, the $S_{\rm{V}}$=1/2 at one site is sandwiched by $S_{\rm{Fe}}$=5/2 spins through antiferromagnetic (AF) interactions. The magnetic properties indicate that the dominant AF interactions between the $S_{\rm{V}}$ = 1/2 spins form a gapped singlet state, and the remaining $S_{\rm{Fe}}$ = 5/2 spins cause an AF order. The magnetization curve exhibits a linear increase up to approximately 7 T, and an unconventional 5/6 magnetization plateau appears between 7 T and 40 T. We discuss the differences between the effective interactions associated with the magnetic properties of the present compound and ($o$-MePy-V)FeCl$_4$. We explain the low-field linear magnetization curve through a mean-field approximation of an $S_{\rm{Fe}}$ = 5/2 spin model. At higher field regions, the 5/6 magnetization plateau and subsequent nonlinear increase are reproduced by the $S_{\rm{V}}$ = 1/2 AF dimer, in which a particular internal field is applied to one of the spin sites. The ESR resonance signals in the low-temperature and low-field regime are explained by conventional two-sublattice AF resonance modes with easy-axis anisotropy. These results demonstrate that exchange interactions between $S_{\rm{V}}$ = 1/2 and $S_{\rm{Fe}}$ = 5/2 spins in $[$$o$-MePy-V-($p$-Br)$_2]$FeCl$_4$ realize unconventional magnetic properties with low-field classical behavior and field-induced quantum behavior.

Nonequilibrium Kondo-vs.-RKKY scenarios in nanoclusters

Ultrafast manipulations of magnetic phases are eliciting increasing attention from the scientific community because potentially relevant to the understanding of nonequilibrium phase transitions and to novel technologies. Here, we focus on manipulations applied to magnetic impurities in metallic hosts. By considering small nanoring geometries, we show how currents can induce a dynamical switching between different types of exchange interactions in these systems. Our work thus opens a study window on nonequilibrium Doniach's magnetic phase diagrams, and time-dependent Kondo-vs.-RKKY scenarios.

Frustration in a graphene-like transverse Ising nanoisland

The phase diagrams and the magnetizations of a graphene-like nanoisland described by the transverse Ising model are investigated by the use of the effective-field theory with correlations. The nanoisland is constructed from twenty-six spin-1/2 magnetic atoms with three types of exchange interactions. In this work, the possibility of reentrant phenomena in the system is particularly examined.

Magnetic Anisotropy by Rashba Spin–Orbit Coupling in Antiferromagnetic Thin Films

Magnetic anisotropy in an antiferromagnet (AFM) with inversion symmetry breaking (ISB) is investigated. The magnetic anisotropy energy (MAE) resulting from the Rashba spin-orbit and s-d type exchange interactions is determined for two different models of AFMs. The global ISB model, representing the effect of a surface, an interface, or a gating electric field, results in an easy-plane magnetic anisotropy. In contrast, for a local ISB model, i.e., for a noncentrosymmetric AFM, perpendicular magnetic anisotropy (PMA) arises. Both results differ from the ferromagnetic case, in which the result for PMA depends on the band structure and dimensionality. These MAE contributions play a key role in determining the direction of the Neel order parameter in antiferromagnetic nanostructures, and reflect the possibility of electrical-field control of the Neel vector.

Phase Diagrams in Graphene-like Ising Nanoparticles

The phase diagrams of four graphene-like nanoparticles described by the Ising model are investigated by the use of the effective-field theory with correlations. The particle is represented by a two-dimensional array of spin-1/2 atoms with two types of exchange interactions, J and JS. The effects of surface exchange interaction JS on the phase diagrams are examined. We have found some characteristic behaviours.