### Browsing by Author "Liashko, S. Y."

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Item Energy surface and transition rates in a hexagonal element of spin ice(2017-10-28) Liashko, S. Y.; Uzdin, V. M.; Jónsson, H.; University of Iceland; St. Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO); Department of Applied PhysicsThe energy surface of a hexagonal element of Kagome spin ice consisting of six prolate magnetic islands is investigated as a function of applied magnetic field. Minimum energy paths for magnetic reversals are determined to estimate energy barriers and the transition rates estimated using harmonic transition state theory for magnetic systems. The overall transition rate between equivalent ground states is calculated using the stationary state approximation including all possible transition paths. The calculated transition rates are in close agreement with reported experimental measurements taken in the absence of an applied field. Predictions are made for the change in the energy landscape and transition rates as a magnetic field is applied.Item Models of the energy landscape for an element of shakti spin ice(ST PETERSBURG NATL RESEARCH UNIV INFORMATION TECHNOLOGIES, MECH & OPTICS, 2018-12) Arnalds, U. B.; Liashko, S. Y.; Bessarab, P. F.; Uzdin, V. M.; Jonsson, H.; University of Iceland; St. Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO); St. Petersburg State University; Multiscale Statistical and Quantum Physics; Department of Applied PhysicsMicromagnetic calculations are compared with faster model calculations of interacting nanoscopic magnetic islands representing an element of a shakti spin ice lattice. Several pathways for transitions between equivalent ground states are studied. The model calculations describe the interaction between the islands either with the point dipole approximation, or with a dumbbell approximation where the distance between the two poles is optimized to match the micromagnetic results. The closest agreement in the energy of both local minima as well as transition state configurations where one macrospin has rotated by 90 degrees is obtained with a dumbbell model where the distance between the poles is ca. 20 % smaller than the island length.Item Rate of thermal transitions in kagome spin ice(2016-09-15) Liashko, S. Y.; Uzdin, V. M.; Jónsson, H.; St. Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO); St. Petersburg State University; Department of Applied PhysicsThe rate of thermal transitions in a kagome spin ice element is calculated using harmonic transition state theory for magnetic systems. Each element consists of six prolate magnetic islands. Minimum energy paths on the multidimensional energy surface are found to estimate activation energy. Vibrational frequencies are also calculated to estimate the rate of the various transitions. An overall transition rate between equivalent ground states is calculated by using the stationary state approximation including all possible transition paths. The resulting transition rate is in a good agreement with experimentally measured lifetime.