Photothermal investigation of magnetostatic modes in yttrium iron garnet at high microwave power levels

Laterally resolved magnetostatic mode spectra in an yttrium-iron-garnet single-crystal (0.98 mm×8.40 mm×4.40 mm) were obtained by microwave spectroscopy using the photothermal laser beam deflection technique. For a microwave frequency of 9.33 GHz and a power of 2.2 W, both magnetostatic surface and magnetostatic backward volume wave modes were observed. The lateral variation of these modes can be explained by a modified WKB approximation for the magnetostatic potential and by taking into account the presence of an inhomogeneous demagnetization field inside the sample. At high incident microwave power, a foldover effect in the range of the surface wave modes and one distinctly larger volume wave mode peak occur. The photothermal signal phase provides information on the penetration depth of the surface wave modes