  Recent years have witnessed significant progresses in realizing skyrmions in
chiral magnets1-4 and asymmetric magnetic multilayers5-13, as well as their
electrical manipulation2,7,8,10. Equally important, thermal generation,
manipulation and detection of skyrmions can be exploited for prototypical new
architecture with integrated computation14 and energy harvesting15. It has yet
to verify if skyrmions can be purely generated by heating16,17, and if their
resultant direction of motion driven by temperature gradients follows the
diffusion or, oppositely, the magnonic spin torque17-21. Here, we address these
important issues in microstructured devices made of multilayers:
(Ta_CoFeB_MgO)15, (Pt_CoFeB_MgO_Ta)15 and (Pt_Co_Ta)15 integrated with on-chip
heaters, by using a full-field soft X-ray microscopy. The thermal generation of
densely packed skyrmions is attributed to the low energy barrier at the device
edge, together with the thermally induced morphological transition from stripe
domains to skyrmions. The unidirectional diffusion of skyrmions from the hot
region towards the cold region is experimentally observed. It can be
theoretically explained by the combined contribution from repulsive forces
between skyrmions, and thermal spin-orbit torques in competing with magnonic
spin torques17,18,20,21 and entropic forces22. These thermally generated
skyrmions can be further electrically detected by measuring the accompanied
anomalous Nernst voltages23. The on-chip thermoelectric generation,
manipulation and detection of skyrmions could open another exciting avenue for
enabling skyrmionics, and promote interdisciplinary studies among spin
caloritronics15, magnonics24 and skyrmionics3,4,12.

Mesoscale and Nanoscale Physics;Materials Science