Hysteresis in the RF-Induced Flux Lattice Annealing (RIFLA) of the superconducting state in Pr$_{1.85}$Ce$_{0.15}$CuO$_{4-y}$

We report hysteresis in flux lattice (FL) annealing by an rf magnetic field for the cuprate superconductor Pr$_{1.85}$Ce$_{0.15}$CuO$_{4-y}$. A strained FL is formed by placing the sample in the coil (inductance $L)$ of a tuned NMR probe circuit and rotating the coil and sample in a fixed \textbf{\textit{B}} at low temperature. A series of rf pulses in the coil generates an alternating magnetic field that anneals the FL. It decreases the sample's rf skin depth, which reduces $L$ and increases the resonant frequency ($f)$ of the probe. Rotation in small steps about an axis parallel to the CuO planes and perpendicular to \textbf{\textit{B}} with annealing after each step generates a peak in $f$ whose shape is the same for rotation in both directions (no rotation hysteresis) and is a maximum for \textbf{\textit{B}} parallel to the CuO planes. When rotation is done in both directions without annealing, the substantial hysteresis reported here occurs. This work was supported at UCLA by NSF Grants DMR-0334869 and DMR-0804625, and at U. Maryland by NSF Grant DMR- 0653535.