Amplitude-dependent magnetic stiffness of melt-quenched YBa₂Cu₃O_7-δ superconductors

Experimental results are reported on the differential levitation forces (magnetic stiffness) between permanent rare-earth magnets and high-temperature superconductors. Using a clamped beam cantilever, the amplitude-dependent magnetic stiffness for five configurations of the test magnets has been investigated for the melt-quenched YBa²Cu³O^7-δ(Y123) superconductors in a range of 1 μm-1 mm. The configuration where the moment of the magnet and the direction of motion are perpendicular to the upper surface of the superconductor has the highest stiffness value among the five configurations. Compared with the data from a sintered Y123 superconductor, the magnetic stiffness for the melt-quenched materials has a much higher value and a much weaker dependence on the oscillation amplitudes. The results are compared with the current experimental and theoretical results.