Ab Initio Exchange Interactions and Magnetic Properties of Intermetallic Compound Gd(2)Fe(17-x)Ga(x)

Intermetallic compounds R2Fe17 are perspective for applications as permanent magnets. Technologically these systems must have Curie temperature Tc much higher than room temperature and preferably have easy axis anisotropy. At the moment highest Tc among stoichiometric R2Fe17 materials is 476 K, which is not high enough. There are two possibilities to increase Tc: substitution of Fe ions with non-magnetic elements or introduction of light elements into interstitial positions. In this work we have focused our attention on substitution scenario of Curie temperature rising observed experimentally in Gd(2)Fe(17-x)Ga(x) (x=0,3,6) compounds. In the framework of the LSDA approach electronic structure and magnetic properties of the compounds were calculated. Ab initio exchange interaction parameters within the Fe sublattice for all nearest Fe ions were obtained. Employing the theoretical values of exchange parameters Curie temperatures Tc of Gd(2)Fe(17-x)Ga(x) within mean-field theory were estimated. Obtained values of Tc agree well with experiment. Also LSDA computed values of total magnetic moment coincide with experimental ones.Comment: 4 pages, 4 figures, 4 tables, Proceedings for EASTMAG-2010, June 28 - July 2 2010, Ekaterinburg, Russi

Magnetization and magnetic entropy change of a three-dimensional isotropic ferromagnet near the Curie temperature in the random phase approximation

The behavior of a three-dimensional isotropic Heisenberg ferromagnet in the presence of a magnetic field H is investigated in the random phase approximation (RPA) near the Curie temperature Tc. It is shown that the magnetization M at the Curie temperature Tc is described by the law M(T=Tc)∼H1/5 and the initial magnetic susceptibility χ0 at temperatures T≥Tc is given by χ0(T≥Tc)∼(T-Tc)-2. It means that in the RPA the critical exponents for a three-dimensional Heisenberg ferromagnet coincide with the critical exponents for the Berlin-Kac spherical model of a ferromagnet rather than with the critical exponents of the mean field approximation (MFA). Hence it follows as well that, when a magnetic field H is risen from H=0 to H=Ha, the magnetic entropy SM will be decreased as ΔSM(T=Tc)∼-Ha 4/5 at the Curie temperature Tc and as ΔS M(T>Tc)∼-(T-Tc)-3H a 2 at temperatures T>Tc. © 2013 Elsevier B.V

Theoretical investigation of TbNi_{5-x}Cu_x optical properties

In this paper we present theoretical investigation of optical conductivity for intermetallic TbNi_{5-x}Cu_x series. In the frame of LSDA+U calculations electronic structure for x=0,1,2 and on top of that optical conductivities were calculated. Disorder effects of Ni for Cu substitution on a level of LSDA+U densities of states (DOS) were taken into account via averaging over all possible Cu ion positions for given doping level x. Gradual suppression and loosing of structure of optical conductivity at 2 eV together with simultaneous intensity growth at 4 eV correspond to increase of Cu and decrease of Ni content. As reported before [Knyazev et al., Optics and Spectroscopy 104, 360 (2008)] plasma frequency has non monotonic doping behaviour with maximum at x=1. This behaviour is explained as competition between lowering of total density of states on the Fermi level N(E_F) and growing of number of carriers. Our theoretical results agree well with variety of recent experiments.Comment: 4 pages, 3 figure

Ab initio exchange interactions and magnetic properties of Gd2Fe17 iron sublattice: rhombohedral vs. hexagonal phases

In the framework of the LSDA+U method electronic structure and magnetic properties of the intermetallic compound Gd2Fe17 for both rhombohedral and hexagonal phases have been calculated. On top of that, ab initio exchange interaction parameters within the Fe sublattice for all present nearest and some next nearest Fe ions have been obtained. It was found that for the first coordination sphere direct exchange interaction is ferromagnetic. For the second coordination sphere indirect exchange interaction is observed to be weaker and of antiferromagnetic type. Employing the theoretical values of exchange parameters Curie temperatures Tc of both hexagonal and rhombohedral phases of Gd2Fe17 within Weiss mean-field theory were estimated. Obtained values of Tc and its increase going from the hexagonal to rhombohedral crystal structure of Gd2Fe17 agree well with experiment. Also for both structures LSDA+U computed values of total magnetic moment coincide with experimental ones.Comment: 20 pages, 2 figures; V2 as published in PR

Трансформация системы защитных механизмов психики в системе "Экзистенциальный кризис – субъект»

Статья посвящена исследованию защитных механизмов человека, находящегося в экзистенциальном кризисе. Предложено рассматривать защитные механизмы и совладающее поведение в контексте объединения двух подходов, а именно, психоаналитического и экзистенциального, что делает возможным расширение взгляда на человека и его жизнь. В ходе исследования определившихся кризисных групп, были выделены основные защитные механизмы и coping поведение. Благодаря процедуре факторного анализа были выявлены латентные конструкты, определяющие содержание фактора «защитное поведение». В ходе проведения экзистенциальноаналитического тренинга были исследованы защитные механизмы, их взаимосвязь и трансформация.The article is devoted to researching of defense mechanisms of person who is in an existential crisis. To consider defense mechanisms and coping behavior in the context of combining two approaches, namely, the psychoanalytic and existential, which makes it possible to expand the view of person and his life was proposed. During the study of crisis groups which were determined, the main defense mechanisms and coping behavior were identified. Due to the procedure of factor analysis the latent constructs which determined the content of the factor "defense behavior" were revealed; it’s have become not only defense mechanisms and coping behavior, but the values of normative ideals (negative values). Using ANOVA, dataset obtained in the analysis of defense mechanisms and coping behaviors that are actualized during the existential crisis was analyzed. Has been determined that the main coping behavior is self-control. Besides defense mechanisms that are specific to each of the represented crisis groups were identified. During research the effect of passing the existential-analytical training on respondents who are in different crisis groups, as well as studying the defense mechanisms the crisis group was determined. In this group with the help of regression analysis the systemic relationship between the indicator of the "crisis in the past" and psychological defenses were revealed. Actual defense mechanisms are: reaction formation, regression and displacement, which are directly related to the experience and the overcoming of existential crisis

Training of junior high school students with respiratory diseases in special medical groups

Представлена система обучения учащихся младших классов имеющих заболевания органов дыхания в специальных медицинских группахFind the system of teaching in junior classes of diseases of the respiratory system in special medical group