MAGNETIC-PROPERTIES OF THE 2-DIMENSIONAL TRIANGLES-IN-TRIANGLES KAGOME LATTICE CU9X2(CPA)6 (X=F,CL,BR)

Magnetic properties of the isostructural series of compounds known as Cu9X2(cpa)6 (cpa=carboxypentonic acid; X=F,Cl,Br) are reported as a function of the mu3-halide ion. The interconnection topology within each layer is a hexagonal arrangement of trimeric units, i.e., a ''triangles-in-triangles'' Kagome lattice. Magnetic field dependent susceptibility data in the range 1.7-250 K demonstrate that all three compounds have a magnetic ground state which is highly field dependent at lower temperatures, but that phase transitions to long-range order are not observed down to 1.7 K. Development of 2-D antiferromagnetic models appropriate for the chemical nature and symmetry of the Cu9X2(cpa)6 lattice will require a two J-value solution (intratrimer and intertrimer), and although theoretical results for this type of lattice are as yet unknown, analogies can be clearly drawn to the Kagome problem. The Curie-Weiss temperatures in the range of -250 K strongly suggest spin frustration in the absence of any traditional long-range order. Magnetization studies exhibit an intermediate saturation level corresponding to a ground state of one unpaired spin per unit cell at field values well below 1.0 kG, supporting the conclusion that the two J values are antiferromagnetic.