Abstract
Magnetic skyrmions are topologically protected nanoscale spin textures with particle-like properties. In bulk cubic helimagnets, they appear under applied magnetic fields and condense spontaneously into a lattice in a narrow region of the phase diagram just below the magnetic ordering temperature, the so-called A-phase. Theory, however, predicts skyrmions to be locally stable in a wide range of magnetic fields and temperatures. Our neutron diffraction measurements reveal the formation of skyrmion states in large areas of the magnetic phase diagram, from the lowest temperatures up to the A-phase. We show that nascent and disappearing spiral states near critical lines catalyze topological charge changing processes, leading to the formation and destruction of skyrmionic states at low temperatures, which are thermodynamically stable or metastable depending on the orientation and strength of the magnetic field. Skyrmions are surprisingly resilient to high magnetic fields: the memory of skyrmion lattice states persists in the field polarized state, even when the skyrmion lattice signal has disappeared. These findings highlight the paramount role of magnetic anisotropies in stabilizing skyrmionic states and open up new routes for manipulating these quasi-particles towards energy-efficient spintronics applications.
Highlights
Skyrmions were introduced into science by T.H.R
A ring of scattering appears at μ0H = 14 mT, which evolves with increasing magnetic field into a weak pattern with the six-fold symmetry characteristic of skyrmion lattices (SkLs) scattering.[8]
This is a remarkable result because it implies that a memory of the SkL phase persists at magnetic fields high enough to suppress the SkL
Summary
Skyrmions were introduced into science by T.H.R. Skyrme who has put forward a non-linear meson model in which baryons, such as protons and neutrons, emerge as topological solitons.[1] Importantly, he identified the baryon number with the topological charge of configurations of the meson field. The Skyrme model was applied to describe physical properties of baryons and atomic nuclei,[2] as well as creation and annihilation of baryons assisted by monopoles.[3] Related topological objects have been discovered in many branches of science, including condensed matter physics.[4,5,6,7] The recent observation of magnetic skyrmions,[8,9] which are topologically protected nanoscale spin textures, initiated a new rapidly expanding field of research, called skyrmionics. The use of skyrmions as information bits holds promise of fast, energyefficient and high-density magnetic memory devices.[10,11,12,13,14]
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