Skyrmions at the interface

Phys. Rev. Lett. 112, 067202 (2014)

Magnetism has been observed at the conductive interface of insulating oxide heterostructures such as LaAlO₃/SrTiO₃. However, its microscopic origin remains controversial. Several explanations have been proposed, ranging from the formation of local magnetic moments to itinerant magnetism. Regardless of the specific mechanism that gives rise to magnetic order, Xiaopeng Li and colleagues have now shown that it is possible to describe the magnetism in oxide heterostructures with a phenomenological model based on symmetry arguments, under the assumption that the spin–orbit coupling is weak.

The researchers — who are based at the University of Pittsburgh, University of California, Santa Barbara, and the Chinese Academy of Sciences — first derive the free energy of the system, and then minimize it to find a phase diagram that features a variety of magnetic phases below a spin-ordering transition temperature. The phase diagram is rather complex and includes in-plane ferromagnetic, spiral, cone and skyrmion lattice phases, the appearance of which depend on the strength of a phenomenological coupling parameter g. Of particular interest, the skyrmion state differs from that found in non-centrosymmetric materials such as helimagnetic MnSi, in that it has nodal points that are protected by geometrical and time-reversal symmetries. Magnetic and transport experiments will be able to confirm the presence of these magnetic phases in LaAlO₃/SrTiO₃ heterostructures.