Antiskyrmions and their electrical footprint.

Skyrmionic materials hold the potential for future information technologies. Systems are needed that exhibit high tunability and scalability, with stored data being easy to read and write by means of all-electrical techniques. The electrical detection of antiskyrmions has been challenging to date.
Published in Materials
Antiskyrmions and their electrical footprint.

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Skyrmions are vortex-like magnetic structures that can form in magnetic materials and could be used for data storage. So-called antiskyrmions had also been predicted and recently discovered in Heussler magnets. These can even be stabilized at room temperature in the magnetic field. Scalability plays a major role in technological applications.

In the Heusler material studied, MnPt1.4Sn, the spatial extension of the antiskyrmions (ASKs) is related to the sample thickness and can be deliberately controlled via the sample shape. Thus, they are not detectable in a larger piece of the starting material, but suddenly appear when the material is cut into small pieces of mesoscopic sizes. Unambiguous detection and identification of these antiskyrmions is still quite laborious. Our work describes the path to detect them by means of electrical Hall-effect measurements. We clarify the material thicknesses at which ASKs start emerging in MnPt1.4Sn.

a Schematic visualization of thickness-dependent ASKs induced by magnetic field, Hc axis, in a step-like sample with applied current along the a axis. b False-color SEM images of FIB devices A and B with meander-shape (three thicknesses: d = 11.2, 8.4, and 2.7 μm) and Hall-bar geometry (d = 1.0 μm), respectively, contacted via sputter-deposited gold contacts. (Further details of all investigated devices, dimensions, and fabrication are presented in Supplementary Notes 13). c Hall-resistivity loop of samples A, B, and C with different thicknesses, d, along the c direction with Hc at T = 300 K. d Greyscale MOKE images of Hall-bar transport device F (d = 0.8 μm) at four different fields for up and down sweep, respectively. e In situ Hall loop for the left and right contacts of device F marked by red and black color, respectively.

Due to their unique topology, skyrmions cause an additional voltage in the electrical conduction of the material, i.e., the topological Hall effect. Here we demonstrate for the first time that an unambiguous signature in the Hall effect is detectable, once the ASK phase establishes in crystalline mesoscale structures of Mn1.4PtSn. In a short video sequences (see supplement, link) we showcase the combined visualization and detection of the emergence of the ASK phase by means of magneto-optical Kerr-effect microscopy and electrical transport measurements at room temperature. The signature revealed is comprised of anomalous and topological Hall components, difficult to disentangle unambiguously. Thus, experiments with further reduced dimensions in combination with magnetosensitive techniques such as Lorentz TEM are highly desirable.

Our atomistic spin-dynamic calculations capture the underlying complex magnetism of Mn1.4PtSn, inevitably linked to the emergence of ASKs at high temperatures. The unique interrelation of Ferromagnetic, Antiferromagnetic and Dzyaloshinskii–Moriya interactions render Mn1.4PtSn an exciting magnetic compound with a complex temperature-field phase diagram.  As has been demonstrated before multiple species of skyrmonic textures can emerge depending on the temperature range, the field strength and orientation.

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