Topologically protected spin textures, such as skyrmions1,2 and vortices3,4,
are robust against perturbations, serving as the building blocks for a range of
topological devices5-9. In order to implement these topological devices, it is
necessary to find ultra-small topological spin textures at room temperature,
because small size implies the higher topological charge density, stronger
signal of topological transport10,11 and the higher memory density or
integration for topological quantum devices5-9. However, finding ultra-small
topological spin textures at high temperatures is still a great challenge up to
now. Here we find ultra-small topological spin textures in Fe78Si9B13 amorphous
alloy. We measured a large topological Hall effect (THE) up to above room
temperature, indicating the existence of highly densed and ultra-small
topological spin textures in the samples. Further measurements by small-angle
neutron scattering (SANS) reveal that the average size of ultra-small magnetic
texture is around 1.3nm. Our Monte Carlo simulations show that such ultra-small
spin texture is topologically equivalent to skyrmions, which originate from
competing frustration and Dzyaloshinskii-Moriya interaction12,13 coming from
amorphous structure14-17. Taking a single topological spin texture as one bit
and ignoring the distance between them, we evaluated the ideal memory density
of Fe78Si9B13, which reaches up to 4.44*104 gigabits (43.4 TB) per in2 and is 2
times of the value of GdRu2Si218 at 5K. More important, such high memory
density can be obtained at above room temperature, which is 4 orders of
magnitude larger than the value of other materials at the same temperature.
These findings provide a unique candidate for magnetic memory devices with
ultra-high density.Comment: 26 pages, 4 figure