Sign Of Exchange Interaction Research Articles

Short notes: Inversion of exchange interaction sign of Nd3+ excited states and its manifestation in optical absorption spectra of NdFe3(BO3)4 crystal

Experimental studies and group-theoretical analysis of low-temperature optical absorption spectra of neodymium ferroborate crystal NdFe3(BO3)4 were carried out. It was shown that the sign of exchange interaction with the iron subsystem in an excited state of Nd3+ can be different from that in the ground state.

Spontaneous magnetization of Kagome lattice in Ising model

The spontaneous magnetization of the Kagome lattice in the Ising model is thoroughly investigated. The proof of the fallacy of spontaneous magnetization obtained earlier and repeatedly migrating from publication to publication is given. An exact expression is presented in the standard Onsager form for spontaneous magnetization in the anisotropic case (depending on arbitrary values and the signs of exchange interactions in all three directions on the Kagome lattice). The frustration properties of the Ising model on 2D Kagome lattice comprehensively studied including the conditions for frustration appearance. The properties of 3D Kagome materials (sometimes contradictory) are explained on the basis of obtained rigorous theoretical results.

Frustration and ordering in Ising chain in an external magnetic field with third-neighbor interactions

In this paper, the frustration properties of the Ising model on a one-dimensional monoatomic equidistant lattice in an external magnetic field are investigated, taking into account the exchange interactions of atomic spins at the sites of the first, second, and third neighbors. Exact analytical expressions for the thermodynamic functions of the system are obtained by the Kramers–Wannier transfer-matrix method. A magnetic phase diagram of the ground state of such a spin system is constructed and studied thoroughly. The points and lines of frustrations of the system depending on the values and signs of exchange interactions and on an external magnetic field are found. The criteria for the occurrence of magnetic frustrations in the presence of competition between the energies of exchange interactions and an external magnetic field are formulated. The peculiar features are investigated and the values of entropy and magnetization of the ground state of this model are obtained in the frustration regime and beyond it. Various types of behavior of entropy, magnetization, and magnetic susceptibility depending on the model parameters are revealed.

Decorated Ising Chain in a Magnetic Field

The Kramers–Wannier transfer matrix method is generalized to an arbitrary decoration number of the Ising chain. An exact analytical expression is obtained for the largest eigenvalue of the transfer matrix of a decorated Ising chain in the presence of an external magnetic field. Frustration points and the values of frustration magnetic fields are found that depend on the magnitudes and signs of exchange interactions. Exact expressions are obtained for zero-temperature entropies and zero-temperature magnetizations of the model under consideration. Magnetic phase diagrams of the ground state of the system are constructed for decoration values of d = 1 and d = 2, including those in the absence of a magnetic field. A comparison is made with a decorated square lattice not only in the absence but also in the presence of a magnetic field.

Correlation function of one-dimensional s = 1 Ising model

The temperature behavior of the Fourier transform of the spin-correlation function has been studied in terms of the one-dimensional Ising model taking into account the interaction between the nearest neighbors in the cases of different signs of exchange interactions, magnetic field, and spin. It has been shown that, in the antiferromagnetic model, in the frustration field, the correlation function has a broad maximum and does not take on the form of a delta function as the temperature approaches zero, which indicates the absence of ordering in the system.

Twelve-state Potts model in a magnetic field

In this work, we have obtained an exact solution to the one-dimensional modified 12-state Potts model using the Kramers-Wannier transfer matrix with allowance for the exchange interaction between nearest neighbors in an external magnetic field. Analytical expressions have been derived for the heat capacity, magnetization, magnetic susceptibility, magnetic entropy, and magnetocaloric effect as functions of temperature, magnitude and sign of exchange interaction, and the magnitude and direction of the magnetic field. The behavior of all of these parameters has been investigated in detail using numerical methods. The possibility of applying the results obtained to explain the observed magnetic properties of real cubic magnets with a NaCl structure and easy axes oriented along the [110] crystallographic directions has been discussed.

Evolution of magnetic properties of cladding austenitic steel under irradiation in a reactor

Magnetic properties of samples of austenitic steel ChS-68 cut from the cladding of a fuel element, which was irradiated in a BN-600 fast-neutron reactor to a maximal damage dose of ∼80 displacements per atom (dpa) at temperatures of 370–587°C, have been investigated. It has been established that irradiation with fast neutrons leads to the formation of ferromagnetic microregions, the effective sizes and concentration of which depend on the damage dose. It has been shown that, at damage doses higher than ∼55 dpa, small spontaneous magnetization and magnetization hysteresis, which are characteristic of the ferromagnetic state, appear in the samples. It is assumed that the ferromagnetic microregions are the nuclei of the α′ phase and the radiation-induced segregation microregions, in which the spacing between the nearest iron atoms exceeds the critical distance that determines the change in the sign of exchange interaction. Arguments in favor of this assumption are presented.

FT-EPR study on the sign of exchange interaction in triplet naphthalene-galvinoxyl encounter pair

Chemically induced dynamic electron polarization (CIDEP) created in the quenching of triplet naphthalene by galvinoxyl were investigated by time-resolved Fourier-transform electron paramagnetic resonance (FT-EPR) measurements with monitoring a free induction decay signal of a pulsed microwave irradiation. Transient FT-EPR spectra of galvinoxyl with CIDEP were observed in various nonpolar solvents with different viscosity. A transient FT-EPR signal phase shows remarkable dependence on the viscosity: FT-EPR signal phases were absorption and emission in the solvents with low and high viscosity, respectively. Time evolutions of the FT-EPR signal of galvinoxyl were well simulated by a model of the radical-triplet pair mechanism (RTPM) for CIDEP. A sign of theJ value in the triplet naphthalene-galvinoxyl system in various solvents were discussed on the basis of the sign rule in the RTPM and the transient FT-EPR signal phase. One of possible explanation for the solvent viscosity dependence of the transient FT-EPR signal phase was pressented on the basis of hypothetical model of theJ value.

Effects of crystal structure and on-site Coulomb interactions on the electronic and magnetic structure ofA2Mo2O7(A=Y,Gd, and Nd) pyrochlores

Being motivated by recent experimental studies, we investigate magnetic structures of the Mo pyrochlores ${A}_{2}{\mathrm{Mo}}_{2}{\mathrm{O}}_{7}$ $(A=\mathrm{Y},$ Nd, and Gd) and their impact on the electronic properties. The latter are closely related with the behavior of twelve $\mathrm{Mo}{(t}_{2g})$ bands, located near the Fermi level and well separated from the rest of the spectrum. We use a mean-field Hartree-Fock approach, which combines fine details of the electronic structure for these bands, extracted from the conventional calculations in the local-density approximation, the spin-orbit interaction, and the on-site Coulomb interactions among the $\mathrm{Mo}(4d)$ electrons, treated in the most general rotationally invariant form. The Coulomb repulsion U plays a very important role in the problem, and the semi-empirical value $U\ensuremath{\sim}1.5--2.5\mathrm{eV}$ accounts simultaneously for the metal-insulator (MI) transition, the ferromagnetic (FM)---spin-glass (SG) transition, and for the observed enhancement of the anomalous Hall effect (AHE). The MI transition is mainly controlled by U. The magnetic structure at the metallic side is nearly collinear FM, due to the double exchange mechanism. The transition into the insulating state is accompanied by the large canting of spin and orbital magnetic moments. The sign of exchange interactions in the insulating state is controlled by the Mo-Mo distances. Smaller distances favor the antiferromagnetic coupling, which predetermines the SG behavior in the frustrated pyrochlore lattice. A large AHE is expected in the nearly collinear FM state, near the point of MI transition, and is related with the unquenched orbital magnetization at the Mo sites. We also predict a large magneto-optical effect in the same FM compounds.

Ferromagnetic and spin-wave resonance in Co/Pd/CoNi multilayer films

It has been found that the magnitude and sign of exchange interaction between Co(5 nm) and CoNi(5 nm) ferromagnetic layers through Pd depend on magnetization orientation of ferromagnetic layers. If magnetization is oriented in a layer plane, exchange interaction can be both ferromagnetic and antiferromagnetic. If magnetization orientation is orthogonal to a layer plane, the exchange constant is always positive at dPd dc (dc is the characteristic length).

Synthesis, EPR and ENDOR of [60]fulleropyrrolidine bisadducts with nitroxide addends: magnitude and sign of the exchange interaction.

The magnitude and sign of the electron exchange interaction J between two nitroxide radicals in a series of [60]fullerene bisadducts (trans-4 bisadduct shown) have been measured. The J value correlates with the distance between and the relative orientation of the unpaired electron molecular orbitals.

Hall Effect in Quasi-Binary GdZnxCu1?x Alloys with the Variable Sign of Exchange Interaction

Hall Effect in Quasi-Binary GdZnxCu1?x Alloys with the Variable Sign of Exchange Interaction

Effects of Lewis acid on the sign of exchange interaction of photogenerated radical ion pairs

FTEPR study shows that the sign of the exchange interaction of the radical ion pair including the 4,4′-dimethoxybenzophenone radical anion and 1,4-diazabicyclo[2,2,2]octane (DABCO) radical cation changes from positive to negative by addition of BF3.