ac susceptibility of the quantum critical point mimicking series Li_xMn_(1.96)Li_(0.04)O_4 (x= 0.0,0.1,0.2,0.35,0.5,0.6,0.8,1.0)

摘要

The present work elucidates the series of magnetic phase transitions present in the series of spinel compounds Li_x[Mn_(1.96)Li_(0.04)]O_4 (x=0.0,0.1,0.2,0.35,0.5,0.6,0.8,1.0). These systems display dynamical scaling originating from the presence of magnetic clusters that form below ～70 K. This scaling is similar to what has been observed in the 122 quantum critical point materials containing intrinsic disorder. We study this system using ac susceptibility in order to understand how disorder leads to fragmentation of the magnetic lattice. The Li doped system's antiferromagnetic (AF) ordering sets in below ～70 K; however, for x= 1 this ordering is limited to clusters of Mn~(4+) ions that are weakly coupled to each other. For the intermediate Li concentrations we observe the formation of individual spin clusters consistent with neutron scattering experiments and we find evidence for the coaligning of these clusters for T<20 K. A maximum in the peak of the susceptibility versus Li content between x=0.5 and x=0.35 indicates a crossover from a regime dominated by the cluster dynamics to one in which the long-range order of the delithiated λ-MnO_2 phase begins to emerge. We discuss the magnetic phase diagram pertaining to short-range order in relationship to the dynamic response of these systems as measured by inelastic neutron scattering experiments.