Abstract
Skyrmions are topologically protected non-collinear magnetic structures. Their stability is ideally suited to carry information in, e.g., racetrack memories. The success of such a memory critically depends on the ability to stabilize and manipulate skyrmions at low magnetic fields. The non-collinear Dzyaloshinskii-Moriya interaction originating from spin-orbit coupling drives skyrmion formation. It competes with Heisenberg exchange and magnetic anisotropy favoring collinear states. Isolated skyrmions in ultra-thin films so far required magnetic fields as high as several Tesla. Here, we show that isolated skyrmions in a monolayer of Co/Ru(0001) can be stabilized down to vanishing fields. Even with the weak spin-orbit coupling of the 4d element Ru, homochiral spin spirals and isolated skyrmions were detected with spin-sensitive scanning tunneling microscopy. Density functional theory calculations explain the stability of the chiral magnetic features by the absence of magnetic anisotropy energy.
Highlights
Skyrmions are topologically protected non-collinear magnetic structures
As the spin spirals observed in this work are strongly modified even with small fields, we introduce an alternative method to investigate the chirality employing a combination of tunneling anisotropic magnetoresistance (TAMR) and tunneling magnetoresistance (TMR)
The spin spiral ground state we report results from the competition between Heisenberg exchange and DzyaloshinskiiMoriya interaction (DMI)
Summary
Skyrmions are topologically protected non-collinear magnetic structures Their stability is ideally suited to carry information in, e.g., racetrack memories. The non-collinear Dzyaloshinskii-Moriya interaction originating from spin-orbit coupling drives skyrmion formation It competes with Heisenberg exchange and magnetic anisotropy favoring collinear states. Isolated skyrmions have been observed in a wide range of polycrystalline metallic films such as [Pt/Co/Ir]n11, CoFeB/Ta14 or in systems consisting of dipolar coupled magnetic films, with each of the films having non-symmetric interfaces[15,16]. In these polycrystalline systems, skyrmion mobility can be limited by pinning to the large amount of structural defects. As it has been shown in several theoretical works[1,2,23], a critical DMI Dc is necessary to form spin spirals: pffiffiffiffiffi
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