Frustrated magnetic helices in MnSi-type crystals

The spiral magnetic order in cubic MnSi-type crystals is considered using the model of classical Heisenberg ferromagnetics with an extra interaction of the Dzyaloshinskii-Moriya (DM) type between neighboring atoms. It is found how the wave vector of magnetic helices depends on DM vector. The wave number k determines both the sign and strength of global spiraling whereas locally, within a unit cell, the helical order can be strongly frustrated so that the twist angles between neighboring ferromagnetic layers may be even of different signs. Conical deformations of helices caused by an arbitrary directed external magnetic field is also considered within the same model. The critical field of helix unwinding is found and it is shown that even in the unwound state there remains a residual periodic splay of magnetic moments which can be measured by diffraction methods. It is also demonstrated how the usually used continuous picture of moment distribution can be obtained from the discrete one in a coarse grain approximation.Comment: 22 pages, 2 figure

The neural network art which uses the Hamming distance to measure an image similarity score

This study reports a new discrete neural network of Adaptive Resonance Theory (ART-1H) in which the Hamming distance is used for the first time to estimate the measure of binary images (vectors) proximity. For the development of a new neural network of adaptive resonance theory, architectures and operational algorithms of discrete neural networks ART-1 and discrete Hamming neural networks are used. Unlike the discrete neural network adaptive resonance theory ART-1 in which the similarity parameter which takes into account single images components only is used as a measure of images (vectors) proximity in the new network in the Hamming distance all the components of black and white images are taken into account. In contrast to the Hamming network, the new network allows the formation of typical vector classes representatives in the learning process not using information from the teacher which is not always reliable. New neural network can combine the advantages of the Hamming neural network and ART-1 by setting a part of source information in the form of reference images (distinctive feature and advantage of the Hamming neural network) and obtaining some of typical image classes representatives using learning algorithms of the neural network ART-1 (the dignity of the neural network ART-1). The architecture and functional algorithms of the new neural network ART which has the properties of both neural network ART-1 and the Hamming network were proposed and investigated. The network can use three methods to get information about typical image classes representatives: teacher information, neural network learning process, third method uses a combination of first two methods. Property of neural network ART-1 and ART-1H, related to the dependence of network learning outcomes or classification of input information to the order of the vectors (images) can be considered not as a disadvantage of the networks but as a virtue. This property allows to receive various types of input information classification which cannot be obtained using other neural networks

Weak antiferromagnetic ordering and pure magnetic reflections induced by Dzyaloshinskii-Moriya interaction in MnSi-type crystals

Symmetry analysis of the Dzyaloshinskii-Moriya (DM) interaction in MnSi-type cubic crystals demonstrates that the magnetic moments are tilted periodically, producing a weak antiferromagnetic pattern, when the helix is unwound by magnetic field. The tilt angles of four Mn sublattices are determined by a component of the DM vector perpendicular to that one responsible for helical spiraling; both components have been evaluated using a simple model. It is shown that the tilting should induce pure magnetic reflections 00l, l=2n+1 in neutron or x-ray magnetic scattering, and the structure factors of these "forbidden" reflections are calculated for arbitrary field orientations.Comment: 6 pages, submitted to PR

Neural networks art: solving problems with multiple solutions and new teaching algorithm

A new discrete neural networks adaptive resonance theory (ART), which allows solving problems with multiple solutions, is developed. New algorithms neural networks teaching ART to prevent degradation and reproduction classes at training noisy input data is developed. Proposed learning algorithms discrete ART networks, allowing obtaining different classification methods of input

Obtaining neodymium from melts by electrolysis

The mechanism of electrode reactions at electrochemical obtaining neodymium and neodymium-iron alloy from fluoride oxide systems has been studied. Current-voltage dependences of electrochemical processes in melts containing fluorine salts of lithium, potassium, sodium and neodymium oxide were analyzed. Neodymium current yield values, optimal process variables: current density, temperature, melt composition were determined. Electrolyzers constructions were optimized, experimental-industrial electrolyzer was designed, process instrument flow diagram was develope