in-plane spin texture
of the Co dots (purple arrows) is imprinted into an irradiated Co/Pd region
(light blue)
underneath the dots (tilted blue arrows). Green and yellow arrows indicate the
moments in
the Co/Pd underlayer
and the core region of the (imprinted) vortex, respectively. Major in-plane
(open symbols) and
perpendicular (solid symbols) hysteresis loops are shown for (b) the Co/Pd
underlayer as grown, (c)
the irradiated Co/Pd witness sample and (d) the hybrid Co+Co/Pd sample.
(October 8, 2015)
Abstract
The topological nature of magnetic skyrmions leads to
extraordinary properties that provide new insights into fundamental problems of
magnetism and exciting potentials for novel magnetic technologies. Prerequisite
are systems exhibiting skyrmion lattices at ambient conditions, which have been
elusive so far. Here, we demonstrate the realization of artificial Bloch
skyrmion lattices over extended areas in their ground state at room temperature
by patterning asymmetric magnetic nanodots with controlled circularity on an
underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled
by a tailored magnetic field sequence and demonstrated in magnetometry
measurements. The vortex structure is imprinted from the dots into the
interfacial region of the underlayer via suppression of the PMA by a critical
ion-irradiation step. The imprinted skyrmion lattices are identified directly
with polarized neutron reflectometry and confirmed by magnetoresistance
measurements. Our results demonstrate an exciting platform to explore
room-temperature ground-state skyrmion lattices.
introduction
The unique spin texture in magnetic skyrmions leads to a
host of fascinating phenomena due to the topologically protected quantum state
and emergent electromagnetic field, offering great potential for novel concepts
in low-dissipation magnetic information storage or skyrmionics. For example,
the recent experimental observation that current-driven skyrmion crystal motion
only requires current densities that are several orders of magnitude smaller
than that necessary for typical current-driven domain wall motion, has sparked
intense interest in the field.