A DMI Guide to Magnets Micro-World

Journal of Experimental and Theoretical Physics - Dzyaloshinskii–Moriya interaction, DMI in short, represents an antisymmetric type of magnetic interactions that favor orthogonal orientation...     

Quantum theory as a description of robust experiments: Derivation of the Pauli equation

It is shown that the Pauli equation and the concept of spin naturally emerge from logical inference applied to experiments on a charged particle under the conditions that (i) space is homogeneous (ii) the observed events are logically independent, and (iii) the observed frequency distributions are robust with respect to small changes in the conditions under which the experiment is carried out. The derivation does not take recourse to concepts of quantum theory and is based on the same principles which have already been shown to lead to e.g. the Schrödinger equation and the probability distributions of pairs of particles in the singlet or triplet state. Application to Stern–Gerlach experiments with chargeless, magnetic particles, provides additional support for the thesis that quantum theory follows from logical inference applied to a well-defined class of experiments.     

Simulation of operation modes of a centrifugal conductive magnetohydrodynamic pump

A mathematical model of a centrifugal conductive magnetohydrodynamic (MHD) pump that calculates the distributions of velocity, current density, and pressure along the channel is developed. The viscous forces in the original system of MHD equations are taken into account on the basis of the known square law of the drag for a turbulent flow in a pipe, generalized for the case of plane flows in a channel. Dependences of the drag coefficient on the main governing parameters (metal flow rate, current intensity, and intensity of magnetic induction), which provide the agreement of the calculated and experimental data on the pressure at the pump outlet for different operation modes, are obtained. It is shown that these dependences have a universal character and the proposed model can be used to design pumps of this type and to manage their operation in production industry.     

γ-Mn at the border between weak and strong correlations

We investigate the role of magnetic fluctuations in the spectral properties of paramagnetic γ-Mn. Two methods are employed. The Local Density Approximation plus Dynamical Mean-Field Theory together with the numerically exact quantum Monte-Carlo solver is used as a reference for the spectral properties. Then the same scheme is used with the computationally less demanding perturbative spin-polarized fluctuation-exchange solver in combination with the Disordered Local Moment approach, and photoemission spectra are calculated within the one-step model. It is shown that the formation of local magnetic moments in γ-Mn is very sensitive to the value of Hund’s exchange parameter. Comparison with the experimental photoemission spectra demonstrates that γ-Mn is a strongly correlated system, with the Hubbard band formation, which cannot be described by the perturbative approach. However, minor change of parameters would transform it into a weakly correlated system.     

The Function cosh {(\sqrt{a\,t^2+b})} is Exponentially Convex

Given positive numbers a and b, the function \({\sqrt{at^2+b}}\) is exponentially convex function of t on the whole real axis. Three proofs of this result are presented.     

Ultrafast spin dynamics in multisublattice magnets

We propose a general theoretical framework for ultrafast laser-induced spin dynamics in multisublattice magnets. We distinguish relaxation of relativistic and exchange origin and show that when the former dominates, nonequivalent sublattices have distinct dynamics despite their strong exchange coupling. Even more interesting, in the exchange dominated regime sublattices can show highly counterintuitive transitions between parallel and antiparallel alignment. This allows us to explain recent experiments with antiferromagnetically coupled sublattices, and predict that such transitions are possible with ferromagnetic coupling as well. In addition, we predict that exchange relaxation enhances the demagnetization speed of both sublattices only when they are antiferromagnetically coupled.     

On the structural and magnetic properties of amorphous Fe84−x W x B16 alloys in dependence of W content

A series of rapidly solidificated amorphous Fe_84?x W _x B₁₆ (x=0–5) alloys have been studied. A strictly linear decrease ofH _eff versus concentration of W has been observed by Mössbauer spectroscopy.     

Atomistic processes and the strain distribution in the early stages of thin film growth

Structural relaxations in small Co islands on the Cu(001) surface are investigated performing atomistic calculations. We demonstrate that the strain relief at the metal interface in the early stages of heteroepitaxy is more complicated than suggested by simple considerations based on the small mismatch between the Co and Cu bulk metals. We found that the strain distribution in the surface region near the islands varies strongly on an atomic scale. The effect of strain on the shape of the Co islands is revealed. Diffusion on the top of strained islands and edge diffusion are considered. Received: 10 April 2000 / Accepted: 15 May 2000 / Published online: 7 March 2001