Hybrid Bloch-Néel spiral states in ${\mathrm{Mn}}_{1.4}\mathrm{PtSn}$ probed by resonant soft x-ray scattering

Multiple intriguing phenomena have recently been discovered in tetragonal Heusler compounds, where $D_{2d}$ symmetry sets a unique interplay between Dzyaloshinskii-Moriya (DM) and magnetic dipolar interactions. In the prototype $D_{2d}$ compound ${\mathrm{Mn}}_{1.4}\mathrm{PtSn}$, this has allowed the stabilization of exotic spin textures, such as first-reported antiskyrmions or elliptic Bloch-type skyrmions. Although less attention has so far been given to the low-field spiral state, this remains extremely interesting as a simplest phase scenario on which to investigate the complex hierarchy of magnetic interactions in this materials family. Here, via resonant small-angle soft x-ray scattering experiments on high-quality single crystals of ${\mathrm{Mn}}_{1.4}\mathrm{PtSn}$ at low temperatures, we evidence how the underlying $D_{2d}$ symmetry of the DM interaction in this material is reflected in its magnetic texture. Our studies reveal the existence of a novel and complex metastable phase, which possibly has a mixed character of both the Néel-type cycloid and the Bloch-type helix, that forms at low temperature in zero fields upon the in-plane field training. This hybrid spin-spiral structure has a remarkable tunability, allowing to tilt its orientation beyond high-symmetry crystallographic directions and control its spiral period. These results broaden the richness of the exotic magnetic phase diagram of Heusler $D_{2d}$ materials and extend their tunability, thus, enhancing a relevant playground for further fundamental explorations and potential applications in energy-saving technologies.

Figure 1

REXS patterns measured at 100 K in the (a) initial state (“S0”) and (b) after the in-plane field training (“SI”). The ex situ training field direction is shown in panel (b). (c) Radial and (d) azimuthal (in detector's plane) intensity profiles of the REXS patterns taken in S0 and SI states. $\varphi ={90}^{\circ }$ corresponds to $\mathbf{Q}\parallel [\overline{1}00$]. The solid dark-gray (dashed yellow) curves show the raw (smoothed) data. The curves are offset for clarity. The radial cuts were taken at the azimuthal angles that correspond to the maximal intensity of the Bragg peaks as rectangular stripes with a width of $\mathrm{\Delta }Q\approx 6\times {10}^{-4}$ Å. The azimuthal profiles correspond to the intensity integrated over a thin ring enclosing the peaks.

Figure 2

(a) REXS patterns measured in the state SI at 100, 50, and 20 K. (b) REXS patterns measured on zero-field warming (ZFW) after preparing the SI state at 20 K. (c) Azimuthal profiles of the REXS intensity (integrated within a thin ring enclosing the peaks) extracted from the patterns shown in (a). The data are offset for clarity. (d) Temperature dependence of the azimuthal position ${\varphi }_{\text{c}}$ and width $W_{\varphi }$ of the spiral Bragg peak in the SI state (solid symbols) and on ZFW from the SI state of 20 K (open symbols). The error bars are smaller than the symbol size.

Figure 3

(a) Zero-field REXS pattern measured at 50 K in the SI state with the high-field background subtracted. (b) Radial profiles of the REXS intensity extracted from the horizontal (top curves) and vertical (bottom curves) cuts of the two-dimensional map. The data are offset for clarity. The smoothed signal (dotted orange line) is shown along with the raw data (solid dark-gray line).