ANOMALOUS SPIN-GLASS BEHAVIOR IN THE GEOMETRICALLY FRUSTRATED MAGNET NI-0.75-FLUORMICA

We report the magnetic properties of a fluormica clay intercalated wit h magnetic Ni2+ ions. The composition of the fluormica host is careful ly selected to result in three-quarters Ni2+ filling of a triangular l attice of possible cation gallery sites. Although three-quarters filli ng is consistent with formation of a (2 x 2)R0 degrees superlattice (e .g the kagome lattice), X-ray diffraction studies of the Ni-0.75:fluor mica material show no evidence for superlattice ordering of the Ni2+ i ons. The nearest-neighbor magnetic interaction is antiferromagnetic wi th a Weiss temperature Theta(w) = -8 K. As a consequence of the triang ular coordination of the magnetic ions, Ni-0.75:fluormica has geometri c magnetic frustration. A spin-glass-like transition occurs at T-G = 4 .5 K. We observe anomalous dynamical properties in this glass, includi ng a region of temperature independent magnetization relaxation remini scent of systems in which quantum fluctuations drive the dynamics. We compare and contrast these results with prior experimental and theoret ical work on the analogous compositionally ordered system, the 2D kago me antiferromagnet.