Strong Coupling of an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>Fe</mml:mi></mml:math> - <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>Co</mml:mi></mml:math> Alloy with Ultralow Damping to Superconducting Co-planar Waveguide Resonators

We report on the strong coupling between a metallic ferromagnetic Fe75Co25 thin film patterned element and range of superconducting Nb half-wavelength co-planar waveguide (CPW) resonators. By varying volume ferromagnet we demonstrate that rate scales linearly with square root number spins achieve over 700 MHz, approaching ultrastrong regime. Experiments center conductor width while maintaining constant magnetic verify decreasing increases cooperativity. Our results show frequency dependence is linear fundamental higher order odd harmonics CPW, but differing efficiencies. The promise for scaling planar resonator/magnetic hybrid systems to smaller dimensions.