Reversible ordering and disordering of the vortex lattice in UPt3

When studied by small-angle neutron scattering, the vortex lattice (VL) in UPt3 undergoes a gradual disordering as a function of time due to U-235 fission. This temporarily heats regions of the sample above the critical temperature, where, upon recooling, the vortices remain in a quenched disordered state. The disordering rate is proportional to the magnetic field, suggesting that it is governed by collective VL properties such as the elastic moduli. An ordered VL can be re-formed by applying a small field oscillation, showing that the fission does not cause detectable radiation damage to the UPt3 crystals, even after long exposure.