Search results for "Ferro"
showing 10 items of 2451 documents
Temperature and pressure dependence of the optical absorption in hexagonal MnTe
2000
The absorption edge of hexagonal (NiAs structure) antiferromagnetic MnTe has been measured by means of light transmission experiments carried out at different temperatures in the range 16--420 K $(P=1\mathrm{bar})$ and hydrostatic pressures up to 9 GPa $(T=295\mathrm{K}).$ An indirect band gap has been found, in agreement with previous band-structure calculations, with an energy of ${E}_{\mathrm{ig}}=1.272\ifmmode\pm\else\textpm\fi{}0.013\mathrm{eV}$ at room temperature and pressure. The temperature dependence of the absorption edge is linear above the N\'eel temperature ${T}_{N}=310\mathrm{K},$ with a temperature coefficient $dE/dT=\ensuremath{-}(3.5\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode…
Properties of small antiferromagnetic Ising clusters
1997
Magnetic properties of small antiferromagnetic clusters have been studied by using the Ising model with nearest-neighbour interactions. The number of atoms in the clusters varied between 6 and 30. Several cluster geometries were analysed in detail with the result that there is no generic phase diagram. In an external magnetic field magnetisation can increase with increasing temperature in a considerable temperature range. Magnetisation was found to strongly depend on both the overall geometry of the cluster and on the symmetry of the underlaying lattice structure.
Corner wetting in the two-dimensional Ising model: Monte Carlo results
2003
Square L ? L (L = 24?128) Ising lattices with nearest neighbour ferromagnetic exchange are considered using free boundary conditions at which boundary magnetic fields ? h are applied, i.e., at the two boundary rows ending at the lower left corner a field +h acts, while at the two boundary rows ending at the upper right corner a field ?h acts. For temperatures T less than the critical temperature Tc of the bulk, this boundary condition leads to the formation of two domains with opposite orientations of the magnetization direction, separated by an interface which for T larger than the filling transition temperature Tf (h) runs from the upper left corner to the lower right corner, while for T …
Classical Heisenberg antiferromagnets with nearest and next-nearest neighbor interactions on the face-centered cubic lattice: a model for EuTe?
1989
Magnetic properties of the Heisenberg antiferromagnet with spin quantum numberS→∞ on the face-centered cubic lattice are studied as function of temperature and magnetic field, using molecular field approximation and Monte Carlo methods. In order to model Europiumtelluride, we use isotropic exchange interactions between nearest- and nextnearest neighbors; the values of these exchange constants are taken from experiments. In addition, a pseudo-dipolar anisotropy (truncated after the next-nearest neighbor distance) is included; the molecular field calculations also are performed with the full dipolar of real EuTe in two respects: the structure in zero magnetic field involves 8 sublattices in t…
Ferromagnetism in small clusters.
1991
Magnetization of small ferromagnetic clusters at finite temperatures has been studied using the Ising model and Monte Carlo techniques. The magnetization of finite clusters is reduced from the bulk value, and increases with the external magnetic field and with the cluster size. The results explain qualitatively the recent observations by de Heer, Milani, and Chatelain of the reduction with decreasing cluster size of the average magnetic moment in small iron clusters.
Carrier-induced ferromagnetism in two-dimensional magnetically doped semiconductor structures
2021
We show theoretically that the magnetic ions, randomly distributed in a two-dimensional (2D) semiconductor system, can generate a ferromagnetic long-range order via the RKKY interaction. The main physical reason is the discrete (rather than continuous) symmetry of the 2D Ising model of the spin-spin interaction mediated by the spin-orbit coupling of 2D free carriers, which precludes the validity of the Mermin-Wagner theorem. Further, the analysis clearly illustrates the crucial role of the molecular field fluctuations as opposed to the mean field. The developed theoretical model describes the desired magnetization and phase-transition temperature ${T}_{c}$ in terms of a single parameter, na…
MAGNETIC INTERACTIONS OF CHAINS FORMED BY FERROMAGNETIC SPHERES
2002
General properties of sphere-chain and chain-chain structures are analysed for homogeneously magnetized spheres. For field aligned structures the local maximum of the magnetic force is observed at H0/MS ≈ 0.5. The magnetic saturation effects are accounted by the Frölich-Kennelly law. Outlines of the approximate methodology of multi-chain interaction are given together with the test results.
Mesoscopic Scale Structural Instability in Ferroelectrics
2009
First-principles statistics addressed to structural phase transitions and temperature development of ferroelectric response is derived within the framework of the Fokker-Planck (Smoluchowsky) equation as complementary to the Monte Carlo [R.D King-Smith., D Vanderbilt, Phys. Rev. B 49, 5828–5844 (1994)] and molecular dynamics [T. Nishimatsu, U. V Waghmare, Y. Kawazoe., D. Vanderbilt, arXiv:0804.1853v2] simulations. Illustrative example of is given for 5 × 5 × 5 BaTiO 3 supercell.
Multiferroics by Rational Design: Implementing Ferroelectricity in Molecule-Based Magnets
2012
Multiferroics (MF) are materials that exhibit simultaneouslyseveral ferroic order parameters. Among the multiferroicmaterials, those combining antiferro- or ferroelectricity (FE)and antiferro-, ferri-, or ferromagnetism (FM) within thesame material are highly desirable: the coexistence of thepolar and magnetic orders paves the way towards four-levelmemories while their interactions through the magnetoelec-tric effect makes it possible to control the magnetization byelectric fields and hence to develop electronically tuneablemagnetic devices, which are an essential feature for spin-tronics.
Crystal time-reversal symmetry breaking and spontaneous Hall effect in collinear antiferromagnets
2020
Identification of a previously overlooked spontaneous Hall effect mechanism creates opportunities in low-dissipation spintronics.