Magnetic excitations in the spinel compound Lix[Mn1.96Li0.04]O4 (x=0.2,0.6,0.8,1.0): How a classical system can mimic quantum critical scaling

We present neutron-scattering results on the magnetic excitations in the spinel compounds Lix Mn1.96Li0.04 O4 x=0.2, 0.6, 0.8, 1.0 . We show that the dominant excitations below T 70 K are determined by Mn ions located in clusters, and that these excitations mimic the dynamic scaling found in quantum critical systems that also harbor magnetic clusters, such as CeRu0.5Fe1.5Ge2. We argue that our results for this classical spinel compound suggest that the unusual response at low temperatures as observed in quantum critical systems that have been driven to criticality through substantial chemical doping is at least partially the result of the fragmentation of the magnetic lattice into smaller units.This research is supported by the U. S. Department of Energy, Office of Basic Energy Sciences, and the Division of Materials Sciences and Engineering under Grant No. DEFG02-07ER46381. J. G. is supported by the University of Missouri Research Board Grant No. RB-07-52 . T.V. is supported by the National Science Foundation Grant No. DMR-0339147 and the Research Corporation