Force-Force Correlations in Disordered Magnets

We study experimentally the force-force correlator in Barkhausen experiments. We observe two distinct universality classes, depending on the range of spin interactions. For short-ranged elasticity, we find the universal correlator predicted by the functional renormalization group in $d=2$. For long-ranged elasticity we observe its 1-loop solution. In all cases force-force correlations grow linearly at small distances, as is assumed in the ABBM model, but in contrast to the latter are bounded at large distances. As a consequence, avalanches are anti-correlated, i.e. reduced in size, at short distances.