Photothermal characterization of inhomogeneous ferromagnetic resonance absorption in ferrites

The depth and lateral dependence of ferromagnetic resonance (FMR) microwave absorption of a plate of sintered Ni ferrite has been studied at 9.35 GHz using photoacoustic detection and the photothermal laser-beam deflection technique. The photoacoustic response of the sample has been measured with a microwave input of 200 mW at modulation frequencies from 10 Hz to 5 kHz, corresponding to thermal depths of 200 to 9 μm. A significant depth dependence of the absorbed microwave power density contributing to a conventionally recorded FMR spectrum has been found. Lateral resolved resonance spectra from the same ferrite have been obtained by using the photothermal laser-beam deflection technique with a power input up to 7 W. Spatial dependences of standing-wave body-resonance modes as well as local variations of the demagnetization field inside the sample were observed. The lateral resolution achieved was about 200 μm.