### Browsing by Author "Ivanov, A. V."

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Item Fast and robust algorithm for energy minimization of spin systems applied in an analysis of high temperature spin configurations in terms of skyrmion density(Elsevier Science B.V., 2021-03) Ivanov, A. V.; Uzdin, V. M.; Jónsson, H.; Department of Applied Physics; Multiscale Statistical and Quantum Physics; University of Iceland; St. Petersburg State UniversityAn algorithm for the minimization of the energy of magnetic systems is presented and applied to the analysis of thermal configurations of a ferromagnet to identify inherent structures, i.e. the nearest local energy minima, as a function of temperature. Over a rather narrow temperature interval, skyrmions appear and reach a high temperature limit for the skyrmion density. In addition, the performance of the algorithm is further demonstrated in a self-consistent field calculation of a skyrmion in an itinerant magnet. The algorithm is based on a geometric approach in which the curvature of the spherical domain is taken into account and as a result the length of the magnetic moments is preserved in every iteration. In the limit of infinitesimal rotations, the minimization path coincides with that obtained using damped spin dynamics while the use of limited-memory quasi-newton minimization algorithms, such as the limited-memory Broyden–Fletcher–Goldfarb–Shanno (LBFGS) algorithm, significantly accelerates the convergence.Item Tip-surface interaction and rate of magnetic transitions(2016-09-15) Ivanov, A. V.; Bessarab, P. F.; Uzdin, V. M.; Jónsson, H.; University of Iceland; KTH Royal Institute of Technology; St. Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO); Department of Applied PhysicsCalculations of the interaction between a magnetic tip of an atomic force microscope with a magnetic surface using the non-collinear extension of the Alexander-Anderson model are described. The mechanism and rate of thermally activated magnetic transitions in a cluster of atoms at the tip is investigated. The results are compared with experimental data and found to be in good agreement with measured lifetimes [R. Schmidt et. al., Phys. Rev. B 86, 174402 (2012).]. The results are also compared with previously reported density functional theory calculations.