instituto de matemáticas universidad de sevilla
Antonio de Castro Brzezicki
Curvature–induced effects in ferromagnet nanowires and nanoshells
The influence of the curvilinear geometry on the transport and electromagnetic properties of matter is a hot topic in condensed matter and field theories. In this respect, the investigation of physical effects governing the responses of curved magnetic nanoobjects to electric and magnetic fields is of strong fundamental interest but is also technologically appealing. One can distinguish two groups of curvatureinduced effects in nanomagnets: (i) magnetochiral effects unite the phenomena of curvature-induced chiral symmetry breaking and (ii) topologically induced magnetization patterning appears in curvilinear magnets, where orientation of the effective anisotropy axis is determined by the geometry. We develop a general fully 3D approach to study dynamical and static properties of arbitrary curved ferromagnet nanowires and nanoshells. According to this approach two additional interaction terms appear in the exchange energy functional due to the curvature and torsion in wires (Gaussian and mean curvatures in the case of shells): an effective Dzyaloshinskii-Moriya (DMI) interaction term and a geometrically induced anisotropy term. The magnetochiral effects are originated from the effective DMI while the magnetization patterning is related to the effective anisotropy. Using such an approach we predict the coupling between the geometrical chirality of the system and magnetochirality of magnetization structure, and a series of new effects such as torsion induced modification of the ground state magnetization, the DMI caused splitting in the spin-wave spectrum, the domain wall pinning, the appearance of curvature stabilized skyrmions. The curvature and torsion effects can be efficiently used to control domain walls in curved nanowires by spin currents