Multi-q Mesoscale Magnetism in CeAuSb₂

We report the discovery of a field driven transition from a single-q to multi-q spin density wave (SDW) in the tetragonal heavy fermion compound CeAuSb₂. Polarized along c, the sinusoidal SDW amplitude is 1.8(2)μ_B/Ce for T<<T_N=6.25(10)K with a wave vector q₁=(η,η,1/2) [η=0.136(2)]. For H || c, harmonics appearing at 2q₁ evidence a striped magnetic texture below μ₀H₁=2.78(1) T. Above H₁, these are replaced by coupled harmonics at q₁+q₂=(2η,0,0)+c^* until μ₀H₂=5.42(5)T, where satellites vanish and magnetization nonlinearly approaches saturation at 1.64(2)μ_B/Ce for μ₀H≈7T.