Direct observation of anisotropic magnetic field response of the spin helix in FeGe thin films

Abstract

Spiral spin orders often produce various fascinating phenomena via interaction with electronic structures. Examples include, but are not limited to, multiferroicity and skyrmion formation. Among them, a deformed spiral spin structure, which can be viewed as a periodic sequence of 2$\ensuremath{\pi}$ spin-rotation kinks, can exhibit the functionality of information transmission owing to its phase coherence. This is the chiral magnetic soliton lattice (CSL). Here, the authors have succeeded in building a spin spiral in a thin film of the chiral magnet FeGe, and revealed its characteristic magnetic responses. Magnetic anisotropy and boundary conditions inherent to the epitaxial thin film secure the alignment of the spiral winding direction along the film normal, even under external magnetic fields. This constraint leads to the anisotropic deformation of the spin spiral with respect to the magnetic field direction. Especially, the CSL, which is realized under an in-plane magnetic field, transforms with field between states with different numbers of kinks. The authors clearly demonstrate the deformation by direct observation of the spiral propagation vector by use of the small-angle neutron scattering technique.