Complex Chiral Modulations in FeGe close to Magnetic Ordering

Abstract

We report on small-angle polarized neutron scattering on the cubic helimagnet FeGe under an external field in the vicinity of the onset of long-period spiral magnetic order at $T_c = 278.7$ K. Magnetic field was applied either along the scattering vector or along the neutron beam. We have mapped the $A$-phase boundaries in the field-temperature ($H$-$T$) phase diagram revealed as a hexagonal pattern of Bragg spots. The small angle neutron scattering ascribed to the form-factor of a single skyrmion was observed below $T_c$ in the field range [$H_{Sk1}, H_{Sk2}$] covering the $A$-phase over. Contrary to the $A$-phase boundaries, the values of $H_{Sk1}$ and $H_{Sk2}$ do not depend on either temperature nor the field direction.