  We report the experimental observation of micron-scale magnetic skyrmions at
room temperature in several Pt/Co-based thin film heterostructures designed to
possess a low exchange stiffness, perpendicular magnetic anisotropy, and a
modest interfacial Dzyaloshinskii-Moriya interaction (iDMI). We find both
experimentally and by micromagnetic and analytic modeling that the combined
action of low exchange stiffness and modest iDMI eliminates the energetic
penalty associated with forming domain walls in thin film heterostructures.
When the domain wall energy density approaches negative values, the remanent
domain morphology transitions from a uniform state to a labyrinthian stripe
phase. A low exchange stiffness, indicated by a reduction in the Curie
temperature below 400 K, is achieved in Pt/Co, Pt/Co/Ni, and Pt/Co/Ni/Re
structures by reducing the Co thickness to the ultrathin limit (< 0.3 nm). A
similar effect occurs in thicker Pt/Co/NixCu1-x structures when the Ni layer is
alloyed with Cu. At this transition in domain morphology, skyrmion phases are
stabilized when a small (< 1 mT) perpendicular magnetic field is applied and
current-induced skyrmion motion including the skyrmion Hall effect is observed.
The temperature and thickness-induced morphological phase transitions observed
are similar to the well-studied spin reorientation transition that occurs in
the ultrathin limit, but we find that the underlying energy balances are
substantially modified by the presence of an iDMI.
