Anomalous anisotropic spin-wave propagation in thin manganite films with uniaxial magnetic anisotropy

Manipulation of the spin-wave coherent length is highly desirable to overcome intrinsic damping and to improve functionalities of magnonics materials and devices. In this work, based on angle-resolved propagating spin-wave spectroscopy and micro-focused Brillouin light scattering, we report a giant anisotropy of spin wave propagation in a 20 nm-thick La0.67Sr0.33MnO3 film grown on a NdGaO3 substrate. Vanishing of such anisotropic features in reference experiments where the La0.67Sr0.33MnO3 film is grown on SrTiO3 suggests that the anisotropic spin-wave propagation might be originated from different lattice mismatches of the LSMO film with these two substrates. Interestingly, the decay length and the relaxation time of spin waves are found to be largest when the wavevector is along the [110] crystalline orientation, which is neither at easy nor hard axis related to the in-plane uniaxial magnetic anisotropy. This suggests the possibility of individual control of the magnetic anisotropy and spin-wave anisotropy via strain engineering. Our discovery may enrich the material systems for anisotropic spin wave behavior and promote strain engineering and optimization of versatile magnonic devices.