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Register a new userTuning of magnetic structures topology via single-ion anisotropy and magnetic field in frustrated 2D semiconductors
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The effects of competing magnetic interactions in stabilizing different spin configurations are drawing a renewed attention in order to both unveil emerging topological spin textures and to highlight microscopic mechanisms leading to their stabilization. The possible key role of the two-site exchange anisotropy in selecting specific helicity and vorticity of skyrmionic lattices has only recently been proposed. In this work we explore the phase diagram of a frustrated localized magnet on a two-dimensional centrosymmetric triangular lattice, focusing on the interplay between the two-ion anisotropy (TIA) and the single-ion anisotropy (SIA). The effects of an external magnetic field applied perpendicularly to the magnetic layer are also investigated. By means of Monte Carlo simulations, we find a profusion of different spin configurations, going from trivial to high-order Q skyrmionic and meronic lattices. In closer detail, we find that a dominant role is played by the two-ion over the single-ion anisotropy in determining the planar spin texture, whereas the strength and sign of SIA, together with the magnitude of the magnetic field, tune the perpendicular spin components, mostly affecting the polarity (and, in turn, the topology) of the spin-texture. Our analysis confirms the crucial role of anisotropic symmetric exchange in systems with dominant short-range interactions, at the same time predicting a rich variety of complex magnetic textures that may arise from a fine tuning of competing anisotropic mechanisms.
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The tunability of high-mobility organic semi-conductors (OSCs) holds great promise for molecular spintronics. In this study, we show this extreme variability - and therefore potential tunability - of the molecular gyromagnetic coupling (g-) tensor with respect to the geometric and electronic structure in a much studied class of OSCs. Composed of a structural theme of phenyl- and chalcogenophene (group XVI element containing, five-membered) rings and alkyl functional groups, this class forms the basis of several intensely studied high-mobility polymers and molecular OSCs. We show how in this class the g-tensor shifts, $Delta g$, are determined by the effective molecular spin-orbit coupling (SOC), defined by the overlap of the atomic spin-density and the heavy atoms in the polymers. We explain the dramatic variations in SOC with molecular geometry, chemical composition, functionalization, and charge life-time using a first-principles theoretical model based on atomic spin populations. Our approach gives a guide to tuning the magnetic response of these OSCs by chemical synthesis.
Artificial tuning of dielectric parameters can result from interface conductivity in polycrystalline materials. In ferroelectric single crystals, it was already shown that ferroelectric domain walls can be the source of such artificial coupling. We show here that low temperature dielectric losses can be tuned by a dc magnetic field. Since such losses were previously ascribed to polaron relaxation we suggest this results from the interaction of hopping polarons with the magnetic field. The fact that this losses alteration has no counterpart on the real part of the dielectric permittivity confirms that no interface is to be involved in this purely dynamical effect. The contribution of mobile charges hopping among Fe related centers was confirmed by ESR spectroscopy showing maximum intensity at ca Tsim40 K.
The propagation of edge localized spin waves (E-SWs) in yttrium iron garnet (YIG) microstripes with/without the proximate magnetic microstructures is investigated by micromagnetic simulations. A splitting of the dispersion curve with the presence of permalloy (Py) stripe is also observed. The E-SWs on the two edges of YIG stripe have different wavelengths, group velocities, and decay lengths at the same frequencies. The role of the Py stripe was found to be the source of the inhomogeneous static dipolar field without dynamic coupling with YIG. This work opens new perspectives for the design of innovative SW interference-based logic devices.
We report the low-temperature coexistence in NdFe3(BO3)4 of an incommensurate magnetic phase with a strained commensurate magnetic phase that is primarily at the surface of the crystal. Increasing the temperature or magnetic field decreases the incommensurability and stabilizes the commensurate magnetic phase above Tic ~14 K or Hic = 0.9 T. A comparison to published studies indicates the onset of longitudinal magnetostriction and electric polarization at the magnetic-field-induced transition, which may arise due to a basal plane spin-flop and canting of the moments along the field direction.
In order to control the dimensionality and the topology of the arrangement of magnetic Ru ions, NaCl-type lithium ruthenates have been investigated. Three types of lithium ruthenates, Li$_{3}$RuO$_{4}$, Li$_{2}$RuO$_{3}$, and cubic-Li$_{x}$RuO$_{1+x}$, were synthesized using a hydrothermal method. All of them have NaCl-type structure, but the arrangements of the cations, Li$^{+}$ and Ru$^{5+}$ (or Ru$^{4+}$), differ from each other. Li$_{3}$RuO$_{4}$ with one-dimensional zigzag chains of Ru ions undergoes an antiferromagnetic transition at 66 K and exhibits an irreversibile magnetism below 32 K, where the zero-field-cooled susceptibility differs from the field-cooled susceptibility. Li$_{2}$RuO$_{3}$ with a two-dimensional honeycomb network of Ru ions demonstrates a paramagnetism almost independent of temperature. A novel ruthenate cubic-Li$_{x}$RuO$_{1+x}$, in which Ru and Li randomly occupy the cation sites of NaCl lattice, undergoes a spin-glass transition at 10 K.
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