Dzyaloshinskii-Moriya-type interaction and Lifshitz invariant in Rashba 2D electron gas systems

The origin of chiral magnetic structures in ultrathin films of magnetic metals is analyzed. It is shown that the Lifshitz-type invariant term in the macroscopic thermodynamic potential can be derived from spin-orbit Rashba Hamiltonian in two dimensional electron gas (2DEG). The former is the prerequisite for existence of spin cycloid, skyrmions and other chiral phenomena observed in thin films. The estimation of the period of spin cycloid gives the value of an order of 10 nm that agrees well with the results of scanning probe microscopy observation reported in the literature

Novel Magnetic Photonic Crystal Structures for Magnetic Field Sensors and Visualizers

Optimized one-dimensional (1-D) magnetophotonic crystals greatly increase the sensitivity of magnetooptical sensors, which are widely used in magnetooptical imaging to observe the magnetic domain patterns in magnetic materials, to observe the vortex states in superconductors, to detect small bits in magnetooptical recording media, to visualize defects in ferromagnetic objects, and to measure the value and spatial distribution of stray magnetic fields. This paper examines the properties of such devices operating in the optimized reflection (doubled Faraday rotation) mode and discusses the use of 1-D magnetophotonic crystals as sensors

Unusual magnetoelectric effect in paramagnetic rare-earth langasite

Violation of time reversal and spatial inversion symmetries has profound consequences for elementary particles and cosmology. Spontaneous breaking of these symmetries at phase transitions gives rise to unconventional physical phenomena in condensed matter systems, such as ferroelectricity induced by magnetic spirals, electromagnons, non-reciprocal propagation of light and spin waves, and the linear magnetoelectric (ME) effect - the electric polarization proportional to the applied magnetic field and the magnetization induced by the electric field. Here, we report the experimental study of the holmium-doped langasite, Ho$_{x}$La$_{3-x}$Ga$_5$SiO$_{14}$, showing a puzzling combination of linear and highly non-linear ME responses in the disordered paramagnetic state: its electric polarization grows linearly with the magnetic field but oscillates many times upon rotation of the magnetic field vector. We propose a simple phenomenological Hamiltonian describing this unusual behavior and derive it microscopically using the coupling of magnetic multipoles of the rare-earth ions to the electric field.Comment: 8 pages, 3 figure

On the problem of coexistence of the weak ferromagnetism and the spin flexoelectricity in multiferroic bismuth ferrite

On the example of the prototypical multiferroic bismuth ferrite the microscopic origin of the spin flexoelectricity responsible for the spin cycloid ordering is analyzed. It is shown how the three basic structural distortions corresponding to the frozen-phonon modes of an ideal perovskite lattice result in the coexistence of the spin canting and the spin cycloidal ordering. On the basis of a simple formula for the antisymmetric Dzyaloshinskii-Moriya superexchange the inhomogenous magnetoelectric contribution to the theromodynamic potential is derived and the values of the microscopic parameters corresponding to the spin canting and the spin cycloid are determined