Emergent topological spin structures in the centrosymmetric cubic perovskiteSrFeO3

Abstract

The skyrmion crystal (SkX) characterized by a multiple-q helical spin modulation has been reported as a unique topological state that competes with the single-q helimagnetic order in noncentrosymmetric materials. Here we report the discovery of a rich variety of multiple-q helimagnetic spin structures in the centrosymmetric cubic perovskite SrFeO 3 . On the basis of neutron diffraction measurements, we have identified two types of robust multiple-q topological spin structures that appear in the absence of external magnetic fields: an anisotropic double-q spin spiral and an isotropic quadruple-q spiral hosting a three-dimensional lattice of hedgehog singularities. The present system not only diversifies the family of SkX host materials, but furthermore provides an experimental missing link between centrosymmetric lattices and topological helimagnetic order. It also offers perspectives for integration of SkXs into oxide electronic devices.

Itinerancy-dependent noncollinear spin textures in SrFeO3, CaFeO3 , and CaFeO3/SrFeO3Rogge1, Green2, Sutarto3 et al. 2019Phys. Rev. Materials285150View full textAdd to dashboardCite

“…2(a). Additionally, the reduction in hysteresis at lower temperatures suggests that the critical field for domain rotation increases with decreasing temperature below 40 K and is consistent with previous measurements that showed a critical field of ∼15 T at 4.2 K [14,25]. Similar MR measurements for CaFeO 3 were not possible due to its large resistivity below its Néel temperature (100 K).…”

“…In the first scenario, a second, symmetric scattering peak forms at slightly higher q values, and grows in intensity with decreasing temperature. Such a scenario would be consistent with Ishiwata et al's [14] proposal of a multidomain, double-q structure in Phase I, where each domain includes both a proper screw (q 1 ) and a vertical cycloid (q 2 ) ordering along one of the four 111 directions, where q 1 and q 2 are along different 111 directions, and the magnitude of q 1 is approximately equal to the magnitude of q 2 . In this picture, the two scattering peaks measured along the same [111] direction arise from ordering in different domains: q 1 of proper screw along [111] of one domain orientation and q 2 of vertical cycloid along [111] of another domain orientation.…”

“…Via resonant soft x-ray magnetic diffraction (RXMD), we show that the magnetic Bragg peaks of CaFeO 3 and SrFeO 3 exhibit significantly different behavior as a function of temperature. We discuss the SrFeO 3 results in context of the recently proposed multi-q structures [14], and from this we conclude that our results are consistent with insulating CaFeO 3 supporting a simple multi-domain, single-q structure. By synthesizing CaFeO 3 /SrFeO 3 superlattices with different SrFeO 3 layer thicknesses, we find the CaFeO 3 helical structure is coherent through a single unit cell-thick SrFeO 3 layer but is not coherent when the SrFeO 3 layer is increased to 6 unit cells, even though both compounds support helical mag-netic structures albeit with slightly different wavevector magnitudes.…”

“…However, some materials have neither a DM interaction nor a frustrated lattice, yet still exhibit multi-q spin textures. These include elemental Nd [11], actinide monopnictides such as USb [12,13], and, as very recently demonstrated, the cubic perovskite SrFeO 3 [14]. The underlying source of the multi-q behavior in these materials is unclear but is critical to understand in order to tune the properties of multi-q spin textures.…”

The 2020 skyrmionics roadmap

“…When these challenges are solved chiral non-collinear spin textures could herald the dawn of new all solid-state spintronic memory-storage devices that would have storage capacities, performance and reliability that go well beyond today's technologies. 27…”