Magnetic Textures Stabilized by Strong Spin-Orbit Interactions
Utkan Güngördü, Rabindra Nepal, Kirill Belashchenko, and Alexey Kovalev
Institute for Materials Research, Tohoku University, Japan
Recent progress in material science has resulted in the realization of new magnetic materials in which the magnetization vector follows complex patterns, including magnetic spirals and skyrmion lattices. Magnetic skyrmion is a vortex like configuration of magnetic moments where they reverse their direction in the core by forming a whirling twist (see figure). Because skyrmions are stable at finite temperatures and can be manipulated by electric currents and fields, realization of magnetic skyrmions may open new possibilities for applications in magnetic memories and logic devices.
An underlying requirement for the formation and stability of these complex magnetic patterns is a strong spin-orbit coupling, a relativistic effect that refers to the coupling of electron spin with the orbital angular momentum. The strong spin-orbit coupling may be achieved, for example, in layered magnetic/non-magnetic thin films, layered oxide heterostructures, and in thin ferromagnetic layers deposited on topological insulators – emerging materials which have non-trivial electronic properties.
Nebraska MRSEC researchers in collaboration with a researcher from Tohoku University are performing a theoretical modeling of complex magnetic patterns, which may occur in these systems. Their results demonstrate a rich phase diagram of stable magnetic configurations as functions of crystalline anisotropies, spin-orbit interaction and magnetic field, revealing regions of the phase diagram that have not previously been analyzed. These phases include spirals and skyrmionic lattices of differing symmetries (see figure). These results provide a new insight into complex magnetic configurations and their control through materials properties.
These programs are supported by the National Science Foundation, Division of Materials Research, Materials Research Science and Engineering Program, Grant 1420645.
Left: Direction of the magnetization vector in a skyrmion. The magnetization in the core of the skyrmion is opposite to the magnetization on the outskirts. Right: direction of the magnetization vector, forming a skyrmion lattice, with 4-fold (top) and 6-fold symmetry (bottom).
Highlight InfoDate: Aug. 2015