Fractal spin structures as origin of 1/f magnetic noise in   superconducting circuits
  We analyze recent data on the complex inductance of dc SQUIDs that show 1/f inductance noise highly correlated with conventional 1/f flux noise. We argue that these data imply a formation of long range order in fractal spin structures. We show that these structures appear naturally in a random system of spins with wide distribution of spin-spin interactions. We perform numerical simulations on the simplest model of this type and show that it exhibits $1/f^{1+\zeta}$ magnetization noise with small exponent $\zeta$ and reproduces the correlated behavior observed experimentally. 
K. Kechedzhi, L. Faoro, and L. B. Ioffe
cond-mat.mes-hall cond-mat.dis-nn