Ferromagnetic resonance probe liftoff suppression apparatus

Claim 1

A liftoff suppression apparatus for a ferromagnetic probe comprising in combination: a ferromagnetic resonance probe comprising a sphere of yttrium iron garnet, a loop wire in close proximity to and substantially surrounding said sphere to couple with but not in contact with said sphere, means for applying an RF current to said loop of wire, said ferromagnetic resonance probe having a microwave frequency associted therewith, and a magnet to apply a constant magnetic field to said sphere, a liftoff sensing coil located in close proximity to said sphere but not coupling with the microwave frequency field associated with said sphere due to the RF current flowing in said loop of wire around said sphere, said liftoff sensing coil measuring the amount of liftoof to said ferromagnetic resonance probe from the surface under test and providing a liftoff signal in proportion thereto, a means for measuring eddy currents, said eddy current measuring means receiving said liftoff signal from said liftoff sensing coil, said eddy current measuring means providing a current driver signal in response to said liftoff signal, a current driver means receiving said current driver signal from said eddy current measuring means, said current driver means generating a bias signal in response to said current driver signal, and, a bias field modulating coil positioned around said ferromagnetic resonance probe so that it will couple with said sphere, said bias field modulating coil receiving said bias signal from said current driver means, said bias signal modulating said bias field modulating coil to modulate the bias field of said ferromagnetic resonance probe so as to counteract the liftoff of said ferromagnetic resonance probe.