Figure 1: Skyrmions in PdFe/Ir(111) (a) Sketch of the experimental setup of a spin-polarized tip probing a magnetic skyrmion. (b) SP-STM topographic image of radially symmetric skyrmions in a perpendicular field of B =-1.5 Tesla (U=+200 mV, I=1 nA, T=2.2 K). (c) Theoretical skyrmion size and shape as a function of the external magnetic field. The magnetic parameters, like the DMi, can be determined by a fit to the experimental magnetic field-dependent data.

Figure 2: Detecting skyrmions with non-magnetic probe tips via NCMR. Sketches of the (a) tunnel magnetoresistance (b) tunneling anisotropic magnetoresistance and the newly discovered (c) non-collinear magnetoresistance. (d) dI/dU map of two skyrmions at B=-2.5 T (U=700 mV, I=1 nA, T=4 K) (e) The local magnetic non-collinearity inside the skyrmion leads to drastic changes of the differential conductance, dI/dU, compared to the collinear ferromagnetic background. Density functional theory (DFT) and tight-binding calculations (CAU) show that the responsible mechanism is the mixing of electronic bands with different spin character.

Figure 3 : Skyrmion lattice phase in Pd/Fe/Ir(111), imaged with NCMR (dI/dU map, U=700 mV). In canted magnetic fields, 1.3 Tesla perpendicular plus (a) 1 Tesla to the left, (b) 1 Tesla to the right, the skyrmions are asymmetrically distorted. This allows to determine the rotational sense (clock-wise rotating), which is in agreement with DFT calculations (CAU).

Figure 4: Distorting skyrmions with magnetic clusters. (a) Undistorted skyrmion. (b,c) Skyrmion pinned by three Co clusters at the same magnetic field (dI/dU maps, U= +700 mV, I=1 nA, T=4.2 K).

Figure 5: Moving skyrmions with magnetic clusters at B=2.1 T, T=8 K. (a) STM topography (b-e) dI/dU maps at +700 mV. The skyrmion is pinned to the Co cluster and closely follows when the cluster is moved by the STM tip, see red circle.

Figure 6: Deleting and writing magnetic skyrmions in three Fe layers on Ir(111) with local electric fields. (a) Deleting with local voltage ramps up to -3 V and (b) writing with +3 V. (c) Model of the spin configuration. The skyrmion shape reflects the symmetry of the atomic lattice. (d) Typical skyrmion spin configuration in an isotropic film.

Figure 7: Interfacial DMi in asymmetric magnetic multilayers. a, Top left: the DMi for two magnetic atoms (grey spheres) close to an atom with a large spin–orbit coupling (blue sphere) in the Fert–Levy picture. Top right: zoom-in on a single trilayer. It is composed of a magnetic layer (FM, grey) between two different heavy metals A (blue) and B (green) inducing the same chirality (same orientation of D) when A is below and B above the magnetic layer. The bottom shows a zoom-in of an asymmetric multilayer made of several repetitions of the trilayer. b–e), A 1.5 × 1.5 µm2 out-of-plane magnetization (mz ) map obtained by STXM on a (Ir|Co|Pt)x10 multilayer at r.t. for in-situ out-of-plane magnetic fields of 8 (b), 38 (c), 68 (d) and 83 (e) mT. The actual image size of the insets is 360 nm. In f) we see the X-ray magnetic circular dichroism (XMCD) signal through a magnetic circular domain (skyrmion) observed at 22 mT (black dots). The blue dashed curve is the magnetization profile of an ideal 60-nm-diameter skyrmion and the red curve derives from the model described in the text. G) We show the same at 58 mT and the corresponding simulation of a 40-nm-diameter skyrmion. The data from f) and g) come from the same skyrmion evolution under the magnetic field.

Figure 8: Magnetic skyrmions in patterned nanoscale disks and tracks. a) Magnetic field evolution of the skyrmion size derived from micromagnetic simulations realized for A = 10 pJ.m–1 (lines for different |D| values) and the experimentally determined sizes of the observed skyrmions (squares) for 500-nm-diameter disks. B) Left: Room temperature (R.T.) out-of-plane magnetization map of 300-nm- diameter disks at a bias out-of-plane external field of µ0H? = 8 mT. Right: 200-nm-wide nanowires (“racetracks”) at µ0H? ˜ 55 mT that display several isolated skyrmions.

Figure 9: Thermal stability investigation of skyrmions by X-ray imaging at variable sample temperatures. a) Curved nanowire and adjacent nucleation pads made from ||Pt10|(Ir1|Co0,8|Pt1)x20|Pt8 (thickness in nanometers). B) A 6x6 µm magnetic image at 80 bias perpendicular field where a skyrmion state has been nucleated at room temperature (300K). In c) we image the part of the wire indicated in the red square at a very low temperature (100K). We observe the same skyrmion state. We are able to “freeze” the skyrmion temperature from room temperature down to low temperature.

Figure 10: a) Patterned disc-shaped dots and adjacent microcoil. The patterned dots are made of ||Pt10|(Ir1|Co0.6|Pt1)x20|Pt3. The resulting field pulses are perpendicular to the sample plane. b) and c) Scanning transmission X-ray microscopy images, acquired at the Co L3 edge, with a temporal resolution of 100 picoseconds. We see here the initial frame. b) A disc-shaped adjacent to the micro-coil is imaged. It exhibits a multi-skyrmion state. The pulsing scheme excitation uses a 6ns pulse. In c) the excitation uses a longer, 20 ns, pulse and has resulted in loss of magnetic contrast due to heating.

Figure 11: Scanning transmission X-ray microscopy images, acquired at the Co L3 edge, of a Ta(46 Å)/Pt(75 Å)/[Co(4 Å)/Ir(5 Å)/Pt(23 Å)]×10 Ir(13 Å) (a) thin film, and a 1000 nm diameter nanodisc of the same film at (b) 0 mT and (c) -50 mT. Fields are applied perpendicular to the sample plane.

Figure 12: (a) HAADF image of cross-section of 10x multilayer structure showing layers and area (green) for EELS analysis. (b) Elemental distribution in region defined in (a) highlighting well defined active Pt, Ir and Co layers plus substrate (N) and protective layer (Cu). (c) Linetraces of variation of active elements in ML stack.

Figure 13: Schematic of (a) Bloch and (b) Néel wall in thin film with perpendicular magnetic anisotropy. Schematic of Fresnel images of (c) Bloch wall in untilted film and (d) Néel wall in tilted film. The tilt axis is shown by the green line and arrow.

Figure 14 (a) Untilted Fresnel image from 10x multilayer structure showing no magnetic contrast. (b) Fresnelimage from same area as (a) but tilted by 25o in the direction indicated by the by the green axis and arrow,showing magnetic contrast.

Figure 15 (a) Tilted Fresnel image from 10x multilayer structure showing magnetic contrast. (b) Fast Fourier Transform of (a) showing distinct spatial frequency associated with magnetic structure allowing estimate of domain size.

Figure 16. Tilted Fresnel images from 20x multilayer structure showing evolution of domain structure. The objective lens field applied for the different images here is (a) 1040 Oe, (b) 709 Oe, (c) 626 Oe, (d) 545 Oe and(e) 463 Oe.

Figure 17: (top) : the magnetic tip of the MFM is scanning a sample with several perpendicular magnetic domains. (Middle), the shift in the phase induced by the interaction between the tip and the stray-field of the sample. (bottom) : Magnetic contrast obtained with MFM.

Figure 18: (a) Hysteresis loop and 3×3 µm² MFM image after demagnetization and at remanence of Pt10|{Ir1|Co0.6|Pt1}x3/Pt3 and (b) Hysteresis loop and 3×3 µm² MFM image after demagnetization and at remanence of Pt10|{Ir1|Co0.6|Pt1}x20/Pt3.

Figure 19: Room temperature MFM images (3×3 µm²) obtained (a) Pt10|{Ir1|Co0.6|Pt1}x5/Pt3 and (b) Pt10|{Ir1|Co0.6|Pt1}x10/Pt3 under different applied magnetic fields. Before imaging a relatively large negative fiel dis applied and then the field is slowly increased to enable the nucleation of magnetic skyrmions. We can notice here that the field value for which skyrmions are stabilized two multilayers are responding quite differently to out-of-plane magnetic field.

Figure 20: Hysteresis loop and room temperature MFM image (3×3µm²) after demagnetization and at remanence of Pt10|{Ir1|Co0.6|Pt1}x5/Pt3, (b) Hysteresis loop and MFM image after demagnetization and at remanence of Pt10|{Ir1|Co0.8|Pt1}x5/Pt3 and (b) Hysteresis loop and MFM image after demagnetization and at remanence of Pt10|{Ir1|Co1|Pt1}x5/Pt3.

Figure 21: Room temperature MFM image after demagnetization in a 700 nm wide track fabricated in Ta/Pt/[Co0.8/Ir1/Pt1]x20 multilayers.

Figure 22: (Left) Room temperature MFM image at zero field in a 2 µm wide track fabricated in Pt/{W1/Co0.6/Pt1}x10 multilayers (Middle) MFM images in an array of dots made from the same multilayers at very small perpendicular field; (Right) Isolated skyrmion stabilized at room temperature in a 600 nm diameter dot.

Figure 23 : MFM image at RT in a 500 nm width Hall device made from Pt/{AlOx1/Co0.6/Pt1}x5. By applying magnetic field along the z-direction is possible to stabilize a discrete number of magnetic skyrmion arranged as a chain in the middle of the track.