  Mn1.4PtSn is the first material in which antiskyrmions have been observed in
ultra-thin single crystalline specimens. While bulk crystals exhibit fractal
patterns of purely ferromagnetic domain ordering at room temperature,
ultra-thin Mn1.4PtSn lamellae clearly show antiskyrmion lattices with lattice
spacings up to several $\mu$m. In the work presented here, we systematically
investigate the thickness region from 400 nm to 10 $\mu$m using 100 $\times$
100 $\mu$m$^2$ -wide Mn1.4PtSn plates, and identify the critical
thickness-to-width aspect ratio $\alpha_0 = 0.044$ for the ferromagnetic
fractal domain to the non-collinear texture phase transition. Additionally, we
also explore these non-collinear magnetic textures below the critical aspect
ratio $\alpha_0$ above and below the spin-reorientation transition temperature
$T_{SR}$ while applying variable external magnetic fields. What we find is a
strong hysteresis for the occurrence of an antiskyrmion lattice, since the
antiskyrmions preferentially nucleate by pinching them off from helical stripes
in the transition to the field polarized state.

Materials Science;Strongly Correlated Electrons;Applied Physics