Response of the Skyrmion Lattice in MnSi to Cubic Magnetocrystalline Anisotropies

We report high-precision small angle neutron scatteringof the orientation of the skyrmionlattice in a spherical sample of MnSi under systematic changes of the magnetic field direction. For all field directions the skyrmionlattice may be accurately described as a triple-$\vec{Q}$ state, where the modulus $\vert \vec{Q} \vert$ is constant and the wave vectors enclose rigid angles of $120^{\circ}$. Along a great circleacross $\langle 100\rangle$, $\langle 110\rangle$, and $\langle 111\rangle$ the normal to the skyrmion- lattice planevaries systematically by $\pm3^{\circ}$ with respect to the field direction, while the in-plane alignment displays a reorientation by $15^{\circ}$ for magnetic field along $\langle 100\rangle$. 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 anisotropieson the skyrmionlattice in MnSi.