Experimental study of microwave magnetostatic waves in thin-film yttrium-iron-garnet with a new magnetic-induction probe

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Abstract
A new high spatial-resolution magnetic-induction probe that measures microwave magnetic field patterns of magnetostatic waves in ferrite thin films has been developed. The probe’s sensing element is either a strand of 25.4-μm-diam gold wire wrapped around a plastic support or an aluminum rectangular loop photolithographically fabricated on glass. The gold wire method yielded a smallest size of 120 μm, and the aluminum loops achieved a highest resolution of 45 μm. The probe is designed for studies of amplitude profiles, dispersion relations, and phase-propagation direction. Investigations of magnetostatic surface waves (MSSW) and backward volume waves (MSBVW) propagating in liquid-phase epitaxially (LPE) grown yttrium-iron-garnet (YIG) were conducted. The LPE-YIG sample used was 4.5 μm thick with the [111] direction perpendicular to the surface of the sample. MSSW and MSBVW of 2–4 GHz microwave frequency were launched in the LPE-YIG, 4.1° from the [01̄1] direction. Studies of MSSW were done under uniform and nonuniform in-plane magnetic bias fields. When contrasted to expected spreading due to diffraction, MSSW in uniform bias fields were found to ‘‘focus’’ as the wave propagated. The ‘‘focusing’’ effect was determined by measurement of the microwave magnetic field profile, transverse to the phase-propagation direction, as a function of propagation distance. As the MSSW propagated, the peak value of the profile increased while the profile width decreased until a maximum profile amplitude occurred, after which the MSSW decreased in amplitude and the width increased. With MSSW and MSBVW in constant uniform bias fields, direct measure of the wavelengths at various microwave frequencies yielded the dispersion relation for each type of wave. Determination of the dispersion relation of MSBVW confirmed the backward nature of these waves.