Magnetic properties of two-dimensional triangular arrays of Ni ions in nickel phyllosilicates

Synthetic phyllosilicates, with nickel replacing the magnesium atoms, have been prepared under autogenous pressures at 220 °C. Both 1:1 phyllosilicate, having interlayer spacing of 7 Å, and 2:1 phyllosilicate with 9.4 Å spacing were obtained depending on the metal to silicon ratio. The latter was also expanded to 13.2 Å by use of an amine substituted silicon alkoxide. Dissolution of the silicate precursors was achieved in the presence of fluoride as NH4F or HF. The microcrystalline products were characterised by X-ray diffraction, thermal analysis, transmission microscopy and chemical analyses. All the samples show long range ferromagnetic order below 28 K accompanied by a rounded maximum in the specific heat measurements. At 4 K they show hysteresis in the magnetisation, with a remnant value ranging from 0.8 to 1.5 µB depending on orientation of the applied field and coercive fields up to 3240 Oe.