Collective magnetism at multiferroic vortex domain walls

Topological defects have been playgrounds for many emergent phenomena in complex matter such as superfluids, liquid crystals, and early universe. Recently, vortex-like topological defects with six interlocked structural antiphase and ferroelectric domains merging into a vortex core were revealed in multiferroic hexagonal manganites. Numerous vortices are found to form an intriguing self-organized network. Thus, it is imperative to find out the magnetic nature of these vortices. Using cryogenic magnetic force microscopy, we discovered unprecedented alternating net moments at domain walls around vortices that can correlate over the entire vortex network in hexagonal ErMnO3 The collective nature of domain wall magnetism originates from the uncompensated Er3+ moments and the correlated organization of the vortex network. Furthermore, our proposed model indicates a fascinating phenomenon of field-controllable spin chirality. Our results demonstrate a new route to achieving magnetoelectric coupling at domain walls in single-phase multiferroics, which may be harnessed for nanoscale multifunctional devices.Comment: 18 pages, 10 figure

Development of the high-temperature phase of hexagonal manganites

Quantum Matter and Optic

Magnetic ordering in HoB12 below and above TN

We present results of neutron scattering experiments on frustrated antiferromagnet HoB12 above and below Ne el temperature TN. Diffuse scattering patterns indicate that above TN 7.4K pronounced correlations between neighboring magnetic moments of Ho ions appear, similar to one dimensional 1D magnets. Moreover, the diffuse scattering patterns show a symmetry reduction from fcc to simple cubic. Analogous behavior in three dimensional 3 D systems is not known, although it was predicted by theory. Results below TN and in applied magnetic field, on the other hand, reveal three amplitude modulated incommensurate magnetic structures in this compound. The role of various interactions leading to this behavior above and below TN is being discussed. Additional attention is paid also to r T resistivity dependencies in various magnetic fields close to and above the quantum critical point. PACS 72.15. v; 75.50.Ee; 78.90. t Keywords Rare earth compound; Magnetic structure; Neutron scattering; Electrical resistivit

Perturbed angular correlations investigations on YMnO3 multiferroic manganite

International audienceThe Perturbed Angular Correlation (PAC) technique was applied to study the yttrium local environment in YMnO3 multiferroic manganite. The electric field gradients (EFG) at the Y site have been measured as function of temperature, covering both ferroelectric and magnetic transitions. The results were compared with point charge model (PCM) calculations. The experimental results show two different EFG distributions for all temperatures. Only one can be directly attributed to the yttrium crystalline site in the hexagonal structure

Influence of magnetic on ferroelectric ordering in LuMnO₃

We have studied the influence of antiferromagnetic ordering on the local dielectric moments of the MnO_5 and LuO_7 polyhedra by measuring neutron powder diffraction patterns of LuMnO_3 at temperatures near T_N. We show that the coupling is weak, because the magnetic exchange coupling is predominantly in the ab-plane of the MnO_5 trigonal bipyramids, and the electric dipole moments, originating in the LuO_7 polyhedra, are oriented along the hexagonal c-axis. Anomalies in the dielectric properties near T_N are thus caused by the geometric constraints between the MnO_5 and the LuO_7 polyhedra