Content area
Full Text
ARTICLES
PUBLISHED ONLINE: 24 OCTOBER 2016 | DOI: http://dx.doi.org/10.1038/nphys3914
Web End =10.1038/NPHYS3914
Spiral spin-liquid and the emergence of a vortex-like state in MnSc2S4
Shang Gao1,2, Oksana Zaharko1*, Vladimir Tsurkan3,4, Yixi Su5, Jonathan S. White1,
Gregory S. Tucker1,6, Bertrand Roessli1, Frederic Bourdarot7, Romain Sibille1,8, Dmitry Chernyshov9,
Tom Fennell1, Alois Loidl3 and Christian Regg1,2
Spirals and helices are common motifs of long-range order in magnetic solids, and they may also be organized into more complex emergent structures such as magnetic skyrmions and vortices. A new type of spiral state, the spiral spin-liquid, in which spins uctuate collectively as spirals, has recently been predicted to exist. Here, using neutron scattering techniques, we experimentally prove the existence of a spiral spin-liquid in MnSc2S4 by directly observing the spiral surfacea continuous surface of spiral propagation vectors in reciprocal space. We elucidate the multi-step ordering behaviour of the spiral spin-liquid, and discover a vortex-like triple-q phase on application of a magnetic eld. Our results prove the eectiveness of the J1J2 Hamiltonian on the diamond lattice as a model for the spiral spin-liquid state in MnSc2S4, and also demonstrate a new way to realize a magnetic vortex lattice through frustrated interactions.
Magnetic frustration, where magnetic moments (spins) are coupled through competing interactions that cannot be simultaneously satisfied1, usually leads to highly cooper
ative spin fluctuations2,3 and unconventional long-range magnetic order4,5. An archetypal ordering in the presence of frustration is the spin spiral. Competing interactions and spiral orders give rise to many phenomena in magnetism, including the multitudinous magnetic phases of rare earth metals6, domains with multiferroic properties7,8, and topologically non-trivial structures such as the emergent skyrmion lattice912.
Recently, a new spiral statea spiral spin-liquid in which the ground states are a massively degenerate set of coplanar spin spiralswas predicted to exist in the J1J2 model on the diamond lattice (see Fig. 1a)1315. Although the diamond lattice is bipartite, and therefore unfrustrated at the near-neighbour (J1) level, the second-neighbour coupling (J2) can generate strong competition. For classical spins, mean-field calculations show that when
[notdef]J2/J1[notdef]>0.125 the spiral spin-liquid appears, and that it is signified
by an unusual continuous surface of propagation vectors q in re
ciprocal space (see Fig. 1b for the spiral surface of [notdef]J2/J1[notdef]=0.85).
At finite temperature, thermal fluctuations might select some...