High field ESR measurements of spin gap system MCu2(PO4)2

Submillimeter and millimeter wave ESR measurements of spin gap systems SrCu2(PO4)2 and PbCu2(PO4)2, which have four kinds of dimers, have been performed to investigate the magnetic properties of spin gap systems using the pulsed magnetic field up to 35T. The observed ESR spectra of powder sample SrCu2(PO4)2 show sharp and single peak in the temperature range from 4.2 to 80 K. The anisotropy of the g-values turned out to be very small compared to the usual anisotropic powder spectra of copper compounds. The dynamical properties will be discussed from the temperature dependence measurements.