Metamagnetic transitions of Lu 2 Cu 2 O 5 studied by submillimeter-wave ESR measurement

Lu 2 Cu 2 O 5 is a related substance of Y 2 Cu 2 O 5 which is an unusual copper oxide with two successive metamagnetic transitions. We have performed the antiferromagnetic resonance (AFMR) measurements of Lu 2 Cu 2 O 5 in the millimeter and submillimeter wave region with the pulsed magnetic field up to 16 T at 1.8 K. Our measurements this time are very detailed frequency dependence measurements compared to the previous measurement and we found new AFMR modes which were not observed previously. From the analysis of the observed AFMR modes, we found that the magnetic phase above H cl = 3.1 T in Lu 2 Cu 2 O 5 is different from that in Y 2 Cu 2 O 5 .