We report resistivity and Hall effect measurements in the chiral antiferromagnet EuPtSi. Depending on the magnetic field orientation with respect to the crystallographic axes, EuPtSi presents different topological magnetic phases below the Néel temperature $T_N=4.05\mathrm{K}$. In particular, for a field $H\parallel$ [111], it exhibits the well-known skyrmion lattice A phase inside the conical phase between $T=0.45\mathrm{K}$ and $T_N$ in the field range 0.8–1.4 T. Further outstanding features of EuPtSi are the nanoscale size of its skyrmions (placing EuPtSi in the less common regime of nonadiabatic electron-skyrmion scattering) and its substantial topological Hall effect. Remarkably, the skyrmion phase can be extended down to very low temperatures (lower than 0.1 K) through field-cooling regardless of the cooling rate and of the magnetic history. Similarly the metastability of the A' and B phases ($H\parallel$ [100]) at low temperature is evidenced by our measurements. These results suggest that EuPtSi is a peculiar example where the competition between topological stability and thermal agitation can lead to a metastable quantum skyrmion state.

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• Magnetic order
• Magnetic texture
• Magnetism
• Skyrmions
• Topological order
• Transport phenomena
• Antiferromagnets
• Chiral magnets
• Resistivity measurements