Response of the skyrmion lattice in MnSi to cubic magnetocrystalline anisotropies

Abstract

We report high-precision small angle neutron scattering of the orientation of the skyrmion lattice in a spherical sample of MnSi under systematic changes of the magnetic field direction. For all field directions the skyrmion lattice may be accurately described as a triple-$\vec{Q}$ state, where the modulus $|\vec{Q}|$ is constant and the wave vectors enclose rigid angles of $120^{\circ }$. Along a great circle across $⟨100⟩$, $⟨110⟩$, and $⟨111⟩$ the normal to the skyrmion-lattice plane varies systematically by $\pm 3^{\circ }$ with respect to the field direction, while the in-plane alignment displays a reorientation by $15^{\circ }$ for magnetic field along $⟨100⟩$. Our observations are qualitatively and quantitatively in excellent agreement with an effective potential, that is determined by the symmetries of the tetrahedral point group $T$ and includes contributions up to sixth-order in spin-orbit coupling, providing a full account of the effect of cubic magnetocrystalline anisotropies on the skyrmion lattice in MnSi.