Magnetic phase transition of high-pressure phase (VO)2P2O7 studied by high-field ESR measurements

The high-pressure phase of (VO)2P2O7 (HP-VOPO) is a S=((1)/(2)) Heisenberg antiferromagnetic alternating chain compound with one spin gap. The high-field ESR measurements of the HP-VOPO single crystal have been performed using the pulsed magnetic field up to 30 T. Small anomaly is observed in ESR mode for both a- and b-axis. The linewidth became broad around Bc=20 T when the field is applied along the a- and b-axis. The magnetic state of HP-VOPO above Bc will be discussed