Topological States in Matter

Topologically nontrivial spin textures, mesoscopic spin configurations that cannot be continuously transformed to an elementary magnetic configuration such as a ferromagnet or antiferromagnet, are of interest due to their ability to exhibit magnetic solitons, with topological protection. Such properties have the potential for applications in future data storage and communication devices. For example, spin textures found in materials such as MnSi, Cu2OSe3, Co-Zn-Mn alloys, and GaV4S8, commonly known as skyrmions, are driven by the interplay of atomic-scale exchange interactions, single-ion anisotropy, and an applied magnetic field. Of particular importance to this class of materials is the presence of a Dyaloshinski Moriya interaction allowed by the noncentrosymmetric crystal structures of the aforementioned materials. In this work, we are presenting the experimental efforts that seek to uncover and understand a new class of skyrmion materials that have been predicted to occur due to frustrated exchange interactions. One of the materials we have pursued in this attempt is the element Neodymium which has a double hexagonal crystal structure (space group P63/mmc). We have performed Small-Angle Neutron Scattering studies which have revealed a previously unobserved set of magnetic Bragg peaks with a hexagonal scattering pattern characteristic of a magnetic skyrmion lattice. We have studied the temperature and field dependence of this pattern as well as its appearance in higher Brillouin zones. Another material we have studied is cobalt-doped NiBr2 which is a layered compound with CdCl2 crystal structure (space group R¯3m) with the potential to host a magnetic vortex lattice nucleated by impurities. Through neutron diffraction studies on this compound, we have observed a ring of magnetic scattering appearing around (1 0 0.5) lattice point that becomes more pronounced with higher cobalt doping. With our recent interest in exploring topological states of matter in kagome systems, we have synthesized ScV6Sn6. The compound ScV6Sn6 crystalizes in R6/mmm space group. Here we present our results in finding evidence for the presence of a charge density wave with a modulation vector [1/3 1/3 1/3] below 92 K.

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