Distinct magnetotransport and orbital fingerprints of chiral bobbers

While chiral magnetic skyrmions have been attracting significant attention in the past years, recently, a new type of chiral particle emerging in thin films—a chiral bobber—has been theoretically predicted and experimentally observed. Here, based on theoretical arguments, we uncover that these novel chiral states possess inherent transport fingerprints that allow for their unambiguous electrical detection in systems comprising several types of chiral states. We reveal that unique transport and orbital characteristics of bobbers root in the nontrivial magnetization distribution in the vicinity of the Bloch points, and demonstrate that tuning the details of the Bloch point topology can be used to drastically alter the emergent response properties of chiral bobbers to external fields, which bears great potential for spintronics applications and cognitive computing.

Figure 1

Spin structures of the considered systems. (a) The magnetic structure of the skyrmion tube. The isosurface indicates regions of in-plane magnetization. The color of the spins indicates the polar angle of the magnetization according to the color scale on the right. $h_{\mathrm{S}}$ indicates the slab thickness. (b) The magnetic structure of the twin surface bobber ($h_{\text{B}}=5$). The close-up on the single-surface bobber is shown in (d). $h_{\mathrm{B}}$ stands for the thickness of the bobber and $d_{\mathrm{BB}}$ stands for the distance between the Bloch points of the twin-surface bobber. In (c) the central column of spins of the structure in (b) is shown. (e) Eight nearest spins around the Bloch point at the bottom of a single-surface bobber in (d).

Figure 2

Hall transport properties of chiral bobbers versus skyrmion tubes. (a) Hall conductivity of the ST (black), SSB (red), and TSB (blue) is shown for $h_{\mathrm{S}}=30$ and $h_{\mathrm{B}}=5$ as a function of the Fermi energy $E_{\mathrm{F}}$. (b) Hall conductivity at $E_{\mathrm{F}}=2.1\mathrm{eV}$, marked with a thin dashed line in (a), is plotted as a function of the slab thickness $h_{\mathrm{S}}$. The color code is the same as in (a). The inset shows ${\sigma }_{xy}$ of SSB and TSB textures as a function of the distance between the Bloch points. (c) ${\sigma }_{xy}$ is shown as a function of the height $h_{\mathrm{B}}$ of the SSB (open blue circles) and TSB (solid black circles). $M$ is indicated by the axis on the right as a function of $h_{\mathrm{B}}$ for the SSB (open red squares) and TSB (solid green squares). For very large values of $h_{\mathrm{B}}$ both the SSB and TSB will transform into ST-like systems, thus converging to a common value of the HC.

Figure 3

(a) The magnitude of the Hall conductance of a three-layer slice of the 17-layer-thick film containing a ST, and a SSB ($h_{\mathrm{B}}=5$), as a function of the position of the slice in the film (see text for details). (b) A cut of the local DOS through the middle of the unit cell integrated from $-1.8\mathrm{eV}$ to $-1.7\mathrm{eV}$ [indicated in green in Fig. 2] for a ST, SSB, and TSB with $h_{\mathrm{S}}=30$ and $h_{\mathrm{B}}=5$.