Theoretical seminar | 21 February 2023

Dr. Mariia Trukhanova
Lomonosov Moscow State University, Faculty of Physics, Department of General Physics, Nuclear Safety Institute, Russian Academy of Sciences.
Theoretical Description of the Magnetoelectric Effect of Spin Origin Based on the Many-Particle Quantum Hydrodynamics Method

There is a version of the Landau-Lifshitz equation that takes into account the exchange interaction between atoms. It contains the vector product of the magnetization by the second spatial derivative of the magnetization. We propose a fundamental microscopic derivation of such an equation as part of a system of equations for the evolution of macroscopic characteristics of the medium. Despite the fact that we are considering a crystal lattice in which ions do not move in an ordered manner in space, the resulting equations have the form of the hydrodynamic equations. Based on the Schrodinger-Pauli equation, which describes the dynamics of atoms in the medium, the equations of the evolution of the magnetic moment, which include the contribution of the exchange interaction of particles with spin S=1/2 or S=1, are obtained. Along with the term described above, an additional contribution is obtained from the nematic tensor, which is the average value of the anticommutator of the spin operators for atoms with spin S=1. For magnetic systems with noncollinear spins subject to antisymmetric exchange interactions, we introduce a microscopic expression for the electric polarization vector and derive an equation for the evolution of polarization in an external magnetic field.

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