Through the use of Heisenberg spin-spin interactions, we provide analytical representations for inelastic neutron scattering eigenstates and excitation cross sections of the general S sub(1) - S ...sub(2) spin dimeric systems. Using an exact diagonalization approach to the spin Hamiltonian, we analyze various spin coefficients to provide general representations for the neutron scattering cross sections of two interacting spins. We also provide a generalized method for the determination of S sub(z)-polarized excitations, which produces an approximation for the spin excitations within an applied z-axis magnetic field. These calculations enhance the general understanding of the interactions between two individual or compound spin systems, which can help provide insight into condensed matter systems such as molecular magnets, quantum dots, and spintronic systems, as well as particle physics investigations into quark matter and meson interactions.
This work develops a generalized technique for determining the static and dynamic properties of any non-collinear magnetic system. By rotating the spin operators into the local spin reference frame, ...we evaluate the zeroth, first, and second order terms in a Holstein-Primakoff expansion, and through a Green's functions approach, we determine the structure factor intensities for the spin-wave frequencies. To demonstrate this technique, we examine the spin-wave dynamics of the generalized Villain model with a varying interchain interaction. The new interchain coupling expands the overall phase diagram with the realization of two non-equivalent canted spin configurations. The rotational Holstein-Primakoff expansion provides both analytical and numerical results for the spin dynamics and intensities of these phases.
Assuming Heisenberg interactions and the symmetric case of a spin S-S' pentamer, the energy eigenstates can be determined exactly. With the energies known, the inelastic neutron scattering ...intensities are then calculated for the special case of a 1-1/2 pentamer. Through an analysis of these results, two main insights are gained. (1) Because of symmetry constraints, not all ΔS(tot) = ±1 transitions are accessible by inelastic neutron scattering (INS). This constrains the standard selections rules for magnetic excitations. (2) The INS signatures of magnetic clusters are directly dependent on the state and component that is excited.
Using polarized neutron reflectometry, we observe an induced magnetization of 75 ± 25 kA/m at 10 K in a La(0.7)Sr(0.3)MnO(3) (LSMO)/BiFeO(3) superlattice extending from the interface through several ...atomic layers of the BiFeO(3) (BFO). The induced magnetization in BFO is explained by density functional theory, where the size of band gap of BFO plays an important role. Considering a classical exchange field between the LSMO and BFO layers, we further show that magnetization is expected to extend throughout the BFO, which provides a theoretical explanation for the results of the neutron scattering experiment.
We examine the presence and evolution of magnetic Dirac nodes in the Heisenberg honeycomb lattice. Using linear spin theory, we evaluate the collinear phase diagram as well as the change in the spin ...dynamics with various exchange interactions. We show that the ferromagnetic structure produces bosonic Dirac and Weyl points due to the competition between the interactions. Furthermore, it is shown that the criteria for magnetic Dirac nodes are coupled to the magnetic structure and not the overall crystal symmetry, where the breaking of inversion symmetry greatly affects the antiferromagnetic configurations. The tunability of the nodal points through variation of the exchange parameters leads to the possibility of controlling Dirac symmetries through an external manipulation of the orbital interactions.
In this study, we examine the thermodynamics and spin dynamics of spin-1/2 and spin-3/2 heptamers. Through an exact diagonalization of the isotropic Heisenberg Hamiltonian, we find the closed-form, ...analytical representations for thermodynamic properties, spin excitations, and neutron-scattering structure factors. Furthermore, we investigate the clusterlike excitations of quantum spin heptamer in the three-dimensional pyrochlore lattice material MgCr2O4. Using a spin mapping of the spin-1/2 heptamer excitations, the calculated structure factors of the spin-3/2 heptamer are to be determined, which provides clarification for the spin excitations in MgCr2O4. Overall, this study demonstrates the ability to use the spin mapping of structure factors for small spin systems to analyze more complex structures.
This study examines the effect of distorted triangular magnetic interactions in the kagome lattice. Using a Holstein-Primakoff expansion, we determine the analytical solutions for classical energies ...and the spin-wave modes for various magnetic configurations. By understanding the magnetic phase diagram, we characterize the changes in the spin waves and examine the spin distortions of the ferromagnetic, antiferrimagnetic, and 120° phases that are produced by variable exchange interactions and lead to various noncollinear phases, which provides a deeper understanding of the magnetic fingerprints of these configurations for experimental characterization and identification.
Abstract Steroid hormones have been widely overlooked as controllers of gene expression. Through the mechanisms of gene expression (DNA methylation, histone methylation, and RNAi), we discuss the ...impact of normal reproductive templates on the pulsatility and amplitude of potential gene-regulating treatment protocols. By examining the interactions of estradiol (E2) and progesterone (P4) in women, we propose that changes in physiologic reproductive hormone templates of exposure and timing can affect fertility and even cancer through the silencing or amplification of gene products; such as P53 and Bcl-2 in women. We suggest that uncontrolled hormone levels, due to aging and/or the environment, may be restored to a normal youthful template of gene expression through the fluctuating exogenous application of E2 and P4 that mimic the normal hormonal milieu of reproductive health. Furthermore, we hypothesize that restoration of normal hormone levels may lead to a lower risk of the chronic illnesses of aging and a better quality of life in patients suffering those conditions.
We investigate the effects of two electronic bands at the negative electronic compressibility (NEC) in a two-dimensional electron gas (2DEG). We use a simple homogeneous model with Coulombic ...interactions and first-order multiband coupling to examine the role of effective mass and relative permittivity in relation to the critical carrier density, where compressibility turns negative. We demonstrate that the population of a second band, along with the presence of interband coupling, can dramatically change the crossover carrier density. Given the difficulty in determining and confirming multiband electronic systems, this model provides a potential method for identifying multiband electronic systems using precise bulk electronic properties measurements. To help illustrate this method, we apply our results to the observed NEC in the 2DEG at the LaAlO3/SrTiO3 (LAO/STO) interface and determine that, for the known parameters of LAO/STO, the system is likely a realization of a two-band 2DEG. Furthermore, we provide general limits on the interband coupling with respect to the electronic band population.
We examine the spin-wave (SW) dynamics of Dy/Y multilayers in order to separate the contribution of the Dy-Y interface from that of bulk Dy. The SW frequencies and intensities of bulk Dy are ...determined analytically. When the Dy layers in a multilayer geometry are decoupled, the SW dispersion relations are discontinuous with discrete excitations. With a Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction coupling through the Y spacer, the discrete excitations become dispersive and the main SW branches split due to the multilayer geometry. Regardless of the strength of the intermediate RKKY interaction, the dispersion signature of the bulk remains.
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