Spins in the Vortices of a High Temperature Superconductor
  Neutron scattering is used to characterise the magnetism of the vortices for the optimally doped high-temperature superconductor La(2-x)Sr(x)CuO(4) (x=0.163) in an applied magnetic field. As temperature is reduced, low frequency spin fluctuations first disappear with the loss of vortex mobility, but then reappear. We find that the vortex state can be regarded as an inhomogeneous mixture of a superconducting spin fluid and a material containing a nearly ordered antiferromagnet. These experiments show that as for many other properties of cuprate superconductors, the important underlying microscopic forces are magnetic. 
B Lake (Oak Ridge Natl Lab), G Aeppli (NEC Research Inst), KN Clausen   (Risoe Natl Lab), DF McMorrow (Risoe Natl Lab), K Le...