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Demidov A.A.,Bryansk State Technical University | Volkov D.V.,Moscow State University
Physics of the Solid State | Year: 2011

The magnetic properties of an antiferromagnet with trigonal symmetry, namely, HoFe3(BO3)4, have been investigated theoretically. The calculations have been performed in the molecular field approximation and in the framework of the crystal field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of HoFe3(BO3)4 have been interpreted and good agreement between theory and experiment has been achieved using the obtained theoretical dependences. The spontaneous spin-reorientation transition and the spin-reorientation transition induced by a magnetic field B {norm of matrix} a from the easy-axis to easy-plane state, as well as the spin-flop transition in a magnetic field B {norm of matrix} c, have been described. It has been shown that the spontaneous spin-reorientation transition is a magnetic analog of the Jahn-Teller effect. The temperature dependences of the initial magnetic susceptibility at temperatures ranging from 2 to 300 K, the nonlinear curves of magnetization for B {norm of matrix} c and B ⊥ c in a magnetic field up to 1. 2 T (which indicate the occurrence of first-order phase transitions), and their evolution with variations in the temperature have been described, as well as the temperature and field dependences of the magnetization in a magnetic field up to 9 T. The parameters of the trigonal crystal field for the rare-earth ion Ho3+ and the parameters of the Fe-Fe and Ho-Fe exchange interactions have been determined in the course of interpretation of the experimental data. © 2011 Pleiades Publishing, Ltd. Source


Andriyanov A.I.,Bryansk State Technical University
Journal of Computer and Systems Sciences International | Year: 2016

The nonlinear dynamics of a closed automatic control system with sinusoidal pulse-width modulation is analyzed. As a result of the studies, maps of dynamic modes and bifurcation diagrams are constructed. New types of Border-collision bifurcations are discover. The concept of a design mode for systems of the considered class is introduced. The results of the work make it possible to extend the classification of Border-collision bifurcations. © 2016, Pleiades Publishing, Ltd. Source


Zhusubaliyev Z.T.,Kursk State University | Mosekilde E.,Technical University of Denmark | Andriyanov A.I.,Bryansk State Technical University | Shein V.V.,Kursk State University
Physica D: Nonlinear Phenomena | Year: 2014

The development of switch-mode operated power electronic converter systems has provided a broad range of new effective approaches to the conversion of electric power. In this paper we describe the transitions from regular periodic operation to quasiperiodicity and high-periodic resonance behavior that can be observed in a pulse-width modulated DC/AC converter operating with high feedback gain. We demonstrate the occurrence of two different types of torus birth bifurcations and present a series of phase portraits illustrating the appearance of phase-synchronized quasiperiodicity. Our numerical findings are verified through comparison with an experimental inverter system. The results shed light on the transitions to quasiperiodicity and to various forms of three-frequency dynamics in non-smooth systems. © 2013 Elsevier B.V. All rights reserved. Source


Demidov A.A.,Bryansk State Technical University | Gudim I.A.,RAS Kirensky Institute of Physics | Eremin E.V.,RAS Kirensky Institute of Physics
Journal of Experimental and Theoretical Physics | Year: 2012

The magnetic properties of ferroborate single crystals with substituted compositions Nd 1 - xDy xFe 3(BO 3) 4 (x = 0.15, 0.25) with competing exchange Nd-Fe and Dy-Fe interactions are investigated. For each composition, we observed a spontaneous spin-reorientation transition from the easy-axis to the easy-plane state and step anomalies on the magnetization curves for the spin-flop transition induced by a magnetic field B ∥ c. The measured parameters and effects are interpreted using a unified theoretical approach based on the molecular field approximation and on calculations performed in the crystal-field model for the rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility from T = 2 K to T = 300 K, anomalies on the magnetization curves for B ∥ c in fields up to 1.8 T, and their evolution with temperature, as well as temperature and field dependences of magnetization in fields up to 9 T are described. In the interpretation of experimental data, the crystal-field parameters in trigonal symmetry for the rare-earth subsystem are determined, as well as the parameters of Nd-Fe and Dy-Fe exchange interactions. © Pleiades Publishing, Inc., 2012. Source


Demidov A.A.,Bryansk State Technical University
Physica B: Condensed Matter | Year: 2014

The magnetic properties of trigonal Ho0.5Nd0.5Fe 3(BO3)4 substituted compound with the competitive Ho-Fe and Nd-Fe exchange interactions have been investigated theoretically. The spontaneous spin-reorientation transition near 9 K has been described. The increase in temperature of the spin-reorientation transition in Ho0.5Nd0.5Fe3(BO3)4 to 9 K in comparison with 5 K in HoFe3(BO3)4 was explained. The calculations were performed using a molecular-field approximation and a crystal-field model for the rare-earth subsystem. A good agreement between the experimental and calculated temperature dependences of magnetic susceptibility and heat capacity has been achieved. © 2014 Elsevier B.V. Source

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