High frequency ESR measurements of antiferromagnetic state in quantum spin system Cu2CdB2O6

Abstract The coexistence of a nearly spin-singlet state and antiferromagnetic long-range order (AFLRO) were found in Cu 2 CdB 2 O 6 . The high frequency ESR measurements have been performed by using a millimeter wave vector network analyzer (MVNA; ABmm) with a small cavity in the frequency of 35–100 GHz. The external magnetic field was applied by using a superconducting magnet. Below the temperature of T N = 9.8 K , ESR absorptions were observed. The frequency–field diagram of ESR absorption lines was obtained by the multiple frequency ESR measurements at the temperature of 1.5 K. We analysed these frequency–field relations based on antiferromagnetic resonance (AFMR) of the two-sublattice antiferromagnet with uniaxial type anisotropy. The AFMR mode at zero magnetic field has a finite antiferromagnetic gap of about 38 GHz. The spin-flop magnetic field H c = 1.38 T was estimated. These results are consistent with the coexistence model of a nearly spin-singlet state and AFLRO in Cu 2 CdB 2 O 6 .