Doping effects on the two-dimensional spin dimer compound SrCu2(BO3)(2)

A series of compounds M0.1Sr0.9Cu2(BO3)(2) with Sr substituted by M=Al, La, Na, and Y and YxSr1-xCu2(BO3)(2) with x=0.06, 0.08, 0.10, 0.20, and 0.30 were prepared by solid state reaction. X-ray diffraction analysis showed that these doping compounds are isostructural to SrCu2(BO3)(2). The resistivity at room temperature, the magnetic susceptibility from 1.9 to 300 K in an applied magnetic field of 1.0 T and the specific heat from 1.9 to 25 K in applied fields up to 14 T were measured, respectively. The spin gap is deduced from the low temperature susceptibility as well as the specific heat. It is found that the spin gap is strongly suppressed by magnetic fields and the doping content. No superconductivity is observed in all doping samples.