Stabilizing spin spirals and isolated skyrmions at low magnetic field exploiting vanishing magnetic anisotropy

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.

Topological Hall effect and emergent skyrmion crystal at manganite-iridate oxide interfaces

“…The easy-plane anisotropy for LSMO films has been found to be AS 2 ≈0.21 meV [46] which gives A≈0.09 meV with S=3/2. Therefore, the critical DM interaction strength to realize the skyrmion crystal D c ∼ √ JA [47][48][49] appears in a range 0.3meV D c 0.6 meV. LSMO also has a weak antiferromagnetic coupling [34] which has not been included in our description.…”

Majorana bound states in magnetic skyrmions imposed onto a superconductor

“…The supercurrent that emerges as a consequence of a domain wall in a superconductor-ferromagnet bilayer (we may view skyrmions as a limiting case of general domain wall structures in this regard by continuously shrinking a circular domain to a skyrmion core) will be bounded by J max = cM (d F /δ) [73], where c is the speed of light, M the saturation magnetization, d F the thickness of the magnetic layer, and δ the width of the domain wall (here: related to the skyrmion radius). As we focus on d F δ, where d F may correspond to monoatomic layer thickness [48] whereas δ will be on the order of 10 -100 nanometers, we can expect that J max is insignificant in the thin-film limit. In this limit, vortices may not form spontaneously, but can still be induced by an external out-of-plane magnetic field [67].…”

“…The idea of having an MBS captured inside a skyrmion is very appealing, because the existing tools for skyrmion manipulation could potentially be employed to navigate single Majorana modes. It is particularly note-worthy that a recent experiment [48] has demonstrated the possibility to move individual skyrmions in the plane with a scanning tunneling microscope tip. In that way, one could envision explicit real-space braiding operations with MBS.…”

B–T phase diagram of Pd/Fe/Ir(111) computed with parallel tempering Monte Carlo

“…Skyrmions are also present in Fe (ultra-)thin-films, e.g., Fe monolayer on Ir(111) [20], Pd/Fe bilayer on Ir(111) [9,10,[30][31][32], 3 monolayers of Fe on Ir(111) [33] and Co ultrathin film Co/Ru(0001) [34]. In that case, magnetic interactions can be tuned by the choice of the magnetic film [35,36], the hybridization with the different substrates [11,35,37,38], or optional overlayers [9].…”