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, 1.0͒. These systems display dynamical scaling originating from the presence of magnetic clusters that form below ϳ70 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 ͑AF͒ ordering sets in below ϳ70 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 Շ 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 -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. © 2010 American Institute of Physics. ͓doi:10.1063/1.3367976͔We present ac susceptibility measurements on the series 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, 1.0͒. The interest in this family of materials is twofold. First, there is the practical importance owing to their use as components of light-weight batteries; 1 ease of Li extraction and high voltage properties make them an attractive cathode material. Second, they have become of interest to the quantum critical point ͑QCP͒ community as they have been shown to mimic 2,3 the dynamical scaling observed in some ͑disor-dered͒ QCP systems. [4][5][6] These scaling properties are believed to be directly associated with the presence of magnetic clusters similar to those observed in quantum critical systems. 2 Indications of such cluster formation and freezing out of the dynamics associated with these clusters in Li x ͓Mn 1.96 Li 0.04 ͔O 4 have been seen in neutron scattering measurements; 7 however, neutrons are not able to detect the onset of cluster formation nor easily observe their freezing out. In this paper we explore this magnetic landscape of Li x ͓Mn 1.96 Li 0.04 ͔O 4 via ac susceptibility measurements, and we show that the neutron scattering based inferences regarding the magnetic clusters are born out by our susceptibility measurements.We briefly review what is known about short and longrange magnetism in Li x ͓Mn 1.96 Li 0.04 ͔O 4 and in its parent compound LiMn 2 O 4 . The structure 8 of the parent compound LiMn 2 O 4 , a network of eightfold Mn 4+ rings surrounded by Mn 3+ ions, shows that clusters are present even in nominally pure samples. Neutron scattering measuremen...