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Thermodynamic properties for Heisenberg ferromagnet with spin-1 on the simple cubic lattice have been calculated using pair approximation method. We introduce the single-ion anisotropy and the next-nearest-neighbor exchange interaction. We found that for negative single-ion anisotropy parameter, the internal energy is positive and heat capacity has two peaks.
Many technologically useful magnetic oxides are ferrimagnetic insulators, which consist of chemically distinct cations. In this work, we examine the spin dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite (Ni 0.65 Zn 0.35 Al 0.8 Fe 1.2 O 4 ) under continuous microwave excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance to separately probe Fe 2+/3+ and Ni 2+ cations on different sublattice sites. Our results show that the precessing cation moments retain a rigid, collinear configuration to within ≈2°. Moreover, the effective spin relaxation is identical to within <10% for all magnetic cations in the ferrite. Thus, we validate the oft-assumed “ferromagnetic-like” dynamics in the resonantly driven ferrimagnetic oxide: the magnetic moments from different cations precess as a coherent, collective magnetization, despite the high contents of nonmagnetic Zn 2+ and Al 3+ diluting the exchange interactions.
Specificities of spin wave focusing in EuO and EuS crystals are studied. It is shown that spin wave focusing is absent in the long-wave approximation: it is observed only for wave vectors in the second half of the Brillouin zone (aq≳ π, where a is the lattice constant and q is the magnitude of the wave vector). It was found that, for EuO and EuS crystals, the directions of spin wave focusing differ due to the different signs of the exchange integrals responsible for the exchange interaction of the magnetic moment with the second neighbors. The directions along which a magnon caustic is formed are determined.
We performed polarization-resolved cross-correlation measurements on a radiative cascade of a charged tri-exciton in a single quantum dot. Photoluminescence spectra showed rich peaks arising from the formation of charged excitonic complexes. The energy structure in the cascade transition of a charged tri-exciton was explained by the exchange interaction. By using one transition pathway of the cascade, whose intermediate states form spin-triplet states, we succeeded in generating three polarization-correlated photons with circular polarization.
Cool and dense prominences found in the solar atmosphere are known to be partially ionized because of their relatively low temperature. In this Letter, we address the long-standing problem of how the neutral component of the plasma in prominences is supported against gravity. Using the multiple-fluid approach, we solve the time-dependent equations in two dimensions considering the frictional coupling between the neutral and ionized components of the magnetized plasma representative of a solar prominence embedded in a hot coronal environment. We demonstrate that given an initial density enhancement in the two fluids, representing the body of the prominence, the system is able to relax in the vicinity of magnetic dips to a stationary state in which both neutrals and ionized species are dynamically suspended above the photosphere. Two different coupling processes are considered in this study: collisions between ions and neutrals and charge exchange interactions. We find that for realistic conditions, ions are essentially static, while neutrals have a very small downflow velocity. The coupling between ions and neutrals is so strong at the prominence body that the behavior is similar to that of a single fluid with an effective density equal to the sum of the ion and neutral species. We also find that the charge exchange mechanism is about three times more efficient at sustaining neutrals than elastic scattering of ions with neutrals.
Shubnikov-de Haas oscillations are studied in 8-nm-wide HgTe/CdHgTe quantum wells with an electron concentration of (1.7–13) × 10{sup 11} cm{sup –2} in the temperature range from 1.6 to 40 K. The gaps between Landau levels and the quantum relaxation time are determined from the temperature dependence of the oscillation amplitude at integer filling factors. The experimental gap values are found to be in good agreement with the results of the single-particle calculation of the level energies using the 8-band Kane model. The experimental widths of the density of states are indicative of profound screening of the exchange interaction in HgTe/CdHgTe quantum wells.
The structural and magnetic properties of thin-film Fe/poly(diphenylene phthalide) (PDP)/Fe systems are studied, along with the behavior of these systems in magnetic fields. The mean surface roughness of the studied samples is around 5–8 nm, and local near-surface magnetic properties show variation within 10%. The samples are characterized by two-step hysteresis loops, the step size depending on the thickness of the polymer layer and the difference in the thickness between the magnetic layers. The results are explained by the effects the exchange interaction between the magnetic layers, mediated by the PDP interlayer, has on the behavior of our samples in a magnetic field.
We present the results of magnetic properties and entanglement for kagome lattice using Heisenberg model with two- and three-site exchange interactions in strong magnetic field. Kagome lattice correspond to the third layer of fluid {sup 3}He absorbed on the surface of graphite. The magnetic properties and concurrence as a measure of pairwise thermal entanglement are studied by means of variational mean-field like treatment based on Gibbs-Bogoliubov inequality. The system exhibits different magnetic behaviors depending on the values of the exchange parameters (J{sub 2}, J{sub 3}). We have obtained the magnetization plateaus at low temperatures. The central theme of the paper is comparing the entanglement and magnetic behavior for kagome lattice. We have found that in the antiferromagnetic region behavior of the concurrence coincides with the magnetic susceptibility one.
The refinement of the Bi{sub 2}O{sub 3}–Fe{sub 2}O{sub 3}–Sb{sub 2}O{sub 5} system phase diagram has been performed and the existence of the two ternary compounds has been confirmed. The first one with a pyrochlore-type structure (sp. gr. Fd 3-barm) exists in the wide solid solution region, (Bi{sub 2−x}Fe{sub x})Fe{sub 1+y}Sb{sub 1−y}O{sub 7±δ}, where x=0.1–0.4 and y=−0.13–0.11. The second one, Bi{sub 3}FeSb{sub 2}O{sub 11}, corresponds to the cubic KSbO{sub 3}-type structure (sp. gr. Pn 3-bar) with unit cell parameter a=9.51521(2) Å. The Rietveld structure refinement showed that this compound is characterized by disordered structure. The Bi{sub 3}FeSb{sub 2}O{sub 11} factor group analysis has been carried out and a Raman spectrum has been investigated. According to magnetization measurements performed at the temperature range 2–300 K it may be concluded that the Bi{sub 3}FeSb{sub 2}O{sub 11} magnetic properties can be substantially described as a superposition of strong short-range antiferromagnetic exchange interactions realizing inside the [(FeSb{sub 2})O{sub 9}] 3D-framework via different pathways. - Graphical abstract: The refinement of the Bi{sub 2}O{sub 3}–Fe{sub 2}O{sub 3}–Sb{sub 2}O{sub 5} system phase diagram has been performed and the existence of the solid solution with a pyrochlore-type structure (sp. gr. Fd 3-barm) and Bi{sub 3}FeSb{sub 2}O{sub 11}, correspond of the cubic KSbO{sub 3}-type structure (sp. gr. Pn 3-bar has been confirmed. The structure refinement, Raman spectroscopy as well as magnetic measurements data of Bi{sub 3}FeSb{sub 2}O{sub 11} are presented. - Highlights: • The Bi{sub 2}O{sub 3}–Fe{sub 2}O{sub 3}–Sb{sub 2}O{sub 5} system phase diagram refinement has been performed. • The Bi{sub 3}FeSb{sub 2}O{sub 11} existence along with pyrochlore structure compound is shown. • It was determined that the Bi{sub 3}FeSb{sub 2}O{sub 11} is of disordered cubic KSbO{sub 3}-type structure. • Factor group analysis of Bi{sub 3}FeSb{sub 2}O{sub 11} vibrational spectrum has been performed. • Short-range antiferromagnetic interactions govern Bi{sub 3}FeSb{sub 2}O{sub 11} magnetic behavior.
We investigate the electron spin dynamics of n-type c-axis oriented bulk zinc oxide (ZnO) by using time-resolved Kerr rotation and resonant spin amplification measurements. Calculating resonant spin amplification using an anisotropic spin dephasing model reveals that there are two species involved in the spin dynamics, which we attribute to conduction and impurity-bound electron spins, respectively. We find that the impurity-bound electron spin dephasing mechanism is strongly anisotropic due to anisotropic exchange interactions. The identification of the two spin species and their dephasing mechanisms is further supported by the temperature, power, and wavelength dependence of the spin coherence measurements.
A theoretical study of the interrelation of the crystal structure, charge, orbital, and magnetic subsystems in R{sub 1 – x}A{sub x}MnO{sub 3} charge-ordered manganites has been carried out (where R{sup 3+} is the rare earth ion, A{sup 2+} is the alkaline earth metal ion, x = 0.5, 2/3). The model of orbital-dependent exchange interactions and single-ion anisotropy is used. The presence of quasi-low-dimensional magnetic structures is exhibited. The spin waves spectra and antiferromagnetic resonance spectra are calculated.
In this work, we treat spin-selective recombination of a geminate radical pair (RP) in a spherical “microreactor,” i.e., of a RP confined in a micelle, vesicle, or liposome. We consider the microreactor model proposed earlier, in which one of the radicals is located at the center of the micelle and the other one undergoes three-dimensional diffusion inside the micelle. In addition, we suggest a two-dimensional model, in which one of the radicals is located at the “pole” of the sphere, while the other one diffuses on the spherical surface. For this model, we have obtained a general analytical expression for the RP recombination yield in terms of the free Green function of two-dimensional diffusion motion. In turn, this Green function is expressed via the Legendre functions and thus takes account of diffusion over a restricted spherical surface and its curvature. The obtained expression allows one to calculate the RP recombination efficiency at an arbitrary magnetic field strength. We performed a comparison of the two models taking the same geometric parameters (i.e., the microreactor radius and the closest approach distance of the radicals), chemical reactivity, magnetic interactions in the RP and diffusion coefficient. Significant difference between the predictions of the two models is found, which is thus originating solely from the dimensionality effect: for different dimensionality of space, the statistics of diffusional contacts of radicals becomes different altering the reaction yield. We have calculated the magnetic field dependence of the RP reaction yield and chemically induced dynamic nuclear polarization of the reaction products at different sizes of the microreactor, exchange interaction, and spin relaxation rates. Interestingly, due to the intricate interplay of diffusional contacts of reactants and spin dynamics, the dependence of the reaction yield on the microreactor radius is non-monotonous. Our results are of importance for (i) interpreting experimental data for magnetic field effects on RP recombination in confined space and (ii) for describing kinetics of chemical reactions, which occur predominantly on the surfaces of biomembranes, i.e., lipid peroxidation reactions.
The competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction is investigated in a double quantum dots system, coupled via a central open conducting region. A perpendicular magnetic field induces the formation of Landau Levels which in turn give rise to the so-called Kondo chessboard pattern in the transport through the quantum dots. The two quantum dots become therefore chirally coupled via the edge channels formed in the open conducting area. In regions where both quantum dots exhibit Kondo transport the presence of the RKKY exchange interaction is probed by an analysis of the temperature dependence. The thus obtained Kondo temperature of one dot shows an abrupt increase at the onset of Kondo transport in the other, independent of the magnetic field polarity, i.e. edge state chirality in the central region.
The structural, optical and magnetic properties of pure and Cr doped ZnS nanoparticles were studied at room temperature. X-ray diffraction analysis confirmed the absence of any mixed phase and the cubic structure of ZnS in pure and Cr doped ZnS nanoparticles. Fourier transfer infrared spectra confirmed the Zn-S stretching bond at 664 cm{sup −1} of ZnS in all prepared nanoparticles. The UV-Visible absorption spectra showed blue shift which became even more pronounced in Cr doped ZnS nanoparticles. However, at relatively higher Cr concentrations a slower red shift was shown by the doped nanoparticles. This phenomenon is attributed to sp-d exchange interaction that becomes prevalent at higher doping concentrations. Further, magnetic hysteresis measurements showed that Cr doped ZnS nanoparticles exhibited ferromagnetic behavior at room temperature.
This study sheds light on the intermolecular interactions between imidazole derive molecules (2-methyl-imidazole, 2-ethyl-imidazole and benzimidazole) intercalated in T[Ni(CN){sub 4}] layers to form a solid of formula unit T(ImD){sub 2}[Ni(CN){sub 4}]. These hybrid inorganic–organic solids were prepared by soft chemical routes and their crystal structures solved and refined from X-ray powder diffraction data. The involved imidazole derivative molecules were found coordinated through the pyridinic N atom to the axial positions for the metal T in the T[Ni(CN){sub 4}] layer. In the interlayers region ligand molecules from neighboring layers remain stacked in a face-to-face configuration through dipole–dipole and quadrupole–quadrupole interactions. These intermolecular interactions show a pronounced dependence on the substituent group and are responsible for an ImD-pillaring concatenation of adjacent layers. This is supported by the structural information and the recorded magnetic data in the 2–300 K temperature range. The samples containing Co and Ni are characterized by presence of spin–orbit coupling and pronounced temperature dependence for the effective magnetic moment except for 2-ethyl-imidazole related to the local distortion for the metal coordination environment. For this last one ligand a weak ferromagnetic ordering ascribed to a super-exchange interaction between T metals from neighboring layers through the ligands π–π interaction was detected. - Graphical abstract: In the interlayers region imidazole derivative molecules are oriented according to their dipolar and quadrupolar interactions and minimizing the steric impediment. Highlights: • Imidazole derivatives intercalation compounds. • Intermolecular interaction between intercalated imidazole derivatives. • Hybrid inorganic–organic solids. • Pi–pi interactions and ferromagnetic coupling. • Dipolar and quadrupolar interactions between intercalated imidazole derivatives.
Y 2 Co 3 is a newly discovered antiferromagnetic (AFM) compound with distorted kagome layers. Here, previous investigations via bulk magnetization measurements suggested a complex non-collinear magnetic behavior, with magnetic moments primarily anti-aligned along the b axis and some canting towards the ac plane. In this study, we report the magnetic structure of Y 2 Co 3 to be an A-type AFM structure with ferromagnetic (FM) interactions within the distorted kagome plane and an inter-plane antiferromagnetic interaction, as determined by single crystal neutron diffraction. The magnetic moments align along the b axis, with minimal canting towards the c axis, at odds with the previous interpretation of bulk magnetization measurements. The magnetic moments on the two distinct Co sites are (0, -0.68, 0) μB and (0, 1.25, 0.07) μ B . We attribute the previously reported ”non-collinear” behavior to the considerable temperature dependence of itinerant AFM exchange interactions, induced by thermal contraction along the b axis. Additionally, our examination of lattice constants through pressure studies reveals compensating effects on FM and AFM interactions, resulting in negligible pressure dependence of T N .
We have prepared Zn{sub 1−x}Co{sub x}S nanoparticles (NPs) and studied their local-geometric, electronic, and magnetic properties. X-ray diffraction analyses have indicated that NPs with average crystallite sizes of 2.2 ∼ 2.9 nm are single phase and crystallize in the zincblende-type structure. Cobalt ions with oxidation state + 2 (Co{sup 2+}) replaced for Zn{sup 2+} and almost unchanged the zincblende-type structure of the ZnS host lattice. Interestingly, all samples show room-temperature ferromagnetism and ferromagnetic order increases with increasing Co content (x) in Zn{sub 1−x}Co{sub x}S NPs. With the results obtained from analyzing the local-geometric structures at Zn and Co K-edges and photoluminescence spectra, we believe that ferromagnetism in Zn{sub 1−x}Co{sub x}S NPs is related to intrinsic defects and exchange interactions between Co{sup 2+} ions. We have also reviewed the recent studies on ZnS-based dilute-magnetic materials.
Heat capacity, Mössbauer and Raman spectra as well as magnetic properties of fluoride CsFe{sub 2}F{sub 6} with defect pyrochlore structure were studied. In addition to recently found above room temperature three successive structural transformations Pnma-Imma-I4{sub 1}amd-Fd-3m, phase transition of antiferromagnetic nature with the 13.7 K Neel temperature and a broad heat capacity anomaly with a maximum at about 30 K were observed. The room temperature symmetry Pnma is unchanged at least down to 7 K. Simple model of indirect bond used to estimate the exchange interactions and to propose a magnetic structure model. - Graphical abstract: The ordered arrangement of Fe{sup 2+} and Fe{sup 3+} ions in high-spin states as well as antiferromagnetic phase transition followed by significant magnetic frustrations were found in pyrocholore-related CsFe{sup 2+}Fe{sup 3+}F{sub 6}. A magnetic structure was proposed using a simple model of indirect bonds. - Highlights: • The Pnma structure in pyrocholore CsFe{sub 2}F{sub 6} is stable down to helium temperature. • Mössbauer spectra confirmed the ordering of Fe{sup 2+} and Fe{sup 3+} ions. • Antiferromagnetic transformation and significant magnetic frustrations are found. • Experimental magnetic entropy agrees with entropy for Fe ions in high-spin state. • Superexchange interactions were calculated and a magnetic structure was proposed.