Computational modeling of sublattice magnetizations of nano-magnetic layered materials

In the present work, we model the salient magnetic properties of the alloy layered ferrimagnetic nanostructures $[Co_{1-c}Gd_c]_{\ell^{\prime}}[Co]_\ell[Co_{1-c}Gd_c]_{\ell^{\prime}}$ between magnetically ordered cobalt leads. The effective field theory (EFT) Ising spin method is used to compute reliable $J_{Co-Co}$ and $J_{Gd-Gd}$ exchange values for the pure cobalt and gadolinium materials in comparison with experimental data. Using the combined EFT and mean field theory (MFT) spin methods, the sublattice magnetizations of the $Co$ and $Gd$ sites on the individual hcp basal planes of the layered nanostructures, are calculated and analyzed. The sublattice magnetizations, effective magnetic moments per site, and compensation characteristics on the individual hcp atomic planes of the embedded nanostructures are presented as a function of temperature and the thicknesses of the layered ferrimagnetic nanostructures, for different stable eutectic concentrations $c\leq$ 0.5. In the absence of first principles calculations for these basic physical variables for the layered nanostructures between cobalt leads, the combined EFT and MFT approach, and appropriate magnetic modeling of the well-defined interfaces of these systems, yield the only available information for them at present. These magnetic variables are necessary for spin dynamic computations, and for the ballistic magnon transport across embedded nanojunctions in magnonics. The model is general, and may applied directly to other composite magnetic elements and embedded nanostructures

Magnons localised on surface steps: a theoretical model

PACS. 75.70.Ak Magnetic properties of monolayers and thin films - 76.70.Hb Optically detected magnetic resonance (ODMR) - 75.30.Et Exchange and superexchange interactions,

Ground state Jahn-Teller effects for V3+ : Al2O 3

A computer analysis of the current experimental data available for ground states of V3+ ions in Al2O3 has been undertaken. It is shown that the new data are satisfactorily accounted for on a multimode lattice Jahn-Teller model in which coupling to the E(Eg) modes dominates.Une analyse à l'ordinateur de l'ensemble des données expérimentales actuelles sur l'état fondamental du système V3+ : Al2O3 est présentée. On montre que ces données sont expliquées de manière satisfaisante par un modèle de l'effet Jahn-Teller du réseau dans lequel le couplage aux modes E(Eg ) est prépondérant

Magnons coherent transmission and its heat transport at ultrathin insulating ferromagnetic nanojunctions

A model calculation is presented for the magnons coherent transmission and corresponding heat transport at magnetic insulating nanojunctions. The system consists of a ferromagnetically ordered ultrathin insulating junction between two semi-infinite ferromagnetically ordered leads. Spin dynamics are analyzed using the equations of motion for the spin precession displacements, valid for the range of temperatures of interest. Coherent scattering cross-sections at the junction boundary are calculated using the phase field matching theory, for all the incidence angles on the boundary from the lead bands, for arbitrary angles of incidence, at variable temperatures, and for different nano thicknesses of the ultrathin junction. The model is general; it is applied in particular to the Fe/Gd/Fe system with a sandwiched ferromagnetic Gd junction. It yields also the thermal conductivity due to the magnons coherent transmission between the two leads when these are maintained at slightly different temperatures. The calculation is carried out for state of the art values of the exchange constants, and elucidates the relation between the coherent scattering transmission of magnons and their thermal conductivity, for different thicknesses

Magnons coherent transmission and its heat transport at ultrathin insulating ferromagnetic nanojunctions

A model calculation is presented for the magnons coherent transmission and corresponding heat transport at magnetic insulating nanojunctions. The system consists of a ferromagnetically ordered ultrathin insulating junction between two semi-infinite ferromagnetically ordered leads. Spin dynamics are analyzed using the equations of motion for the spin precession displacements, valid for the range of temperatures of interest. Coherent scattering cross-sections at the junction boundary are calculated using the phase field matching theory, for all the incidence angles on the boundary from the lead bands, for arbitrary angles of incidence, at variable temperatures, and for different nano thicknesses of the ultrathin junction. The model is general; it is applied in particular to the Fe/Gd/Fe system with a sandwiched ferromagnetic Gd junction. It yields also the thermal conductivity due to the magnons coherent transmission between the two leads when these are maintained at slightly different temperatures. The calculation is carried out for state of the art values of the exchange constants, and elucidates the relation between the coherent scattering transmission of magnons and their thermal conductivity, for different thicknesses

Spin dynamics across an inhomogeneous atomic boundary separating ultrathin Heisenberg ferromagnetic films

A theoretical model is presented for the study of the scattering and the localisation of spin-waves at an extended inhomogeneous structural and magnetic boundary separating ultrathin Heisenberg ferromagnetic films. The model system consists of two different magnetic materials A and B with different thickness of two and three atomic layers, on either side of a defect atomic step. The matching technique is used with nearest neighbour magnetic exchange to analyse both the localisation and the scattering spin dynamics. The localised spin states that manifest themselves as Rayleigh branches, and the local densities of spin states are calculated on this boundary. The coherent reflection and transmission scattering properties of spin-waves incident from the interior of the ultrathin films on the inhomogeneous boundary are also calculated. The numerical calculations are applied in particular to a system of three Fe ferromagnetic atomic layers and two Gd ferromagnetic atomic layers, across a defect atomic step. The results illustrate the occurrence of Fano resonances in the transmitted spectra due to the localised spin states on the inhomogeneous boundary. An interesting physical effect is observed for this magnetic and atomic step boundary, namely the frequency selective conductance of the spin-waves via Fano resonances, by an appropriate choice of the angle of spin-wave incidence on the boundary

ON THE THERMAL AND ELECTRICAL CONDUCTIVITY OF V3Si AND V5Si3

Thermal conductivity and electrical resistivity measurements have been performed on V3Si and V5Si3 single crystals. Thermal conductivity anomalies are observed on both compounds and seem likely to be related to the resistivity "saturation" behaviour exhibited by these two compounds