The low-dimensional spin magnet CaCu2O3 probed by high-field ESR

Abstract Magnetization and high-field electron spin resonance (ESR) response of the s = 1 2 -Heisenberg pseudo-ladder magnet CaCu 2 O 3 is dominated at low temperatures by a few percent of ‘extra’ Cu-spin states arising due to the structural disorder. These ‘extra’ spins interact with the bulk spins and jointly order antiferromagnetically at T N = 26 K . At T T N ESR data reveal a small magnon anisotropy gap of the order of ≲ 1 meV . Substitution of 15% of nonmagnetic Zn for Cu reduces the concentration of ‘extra’ spins and results in the suppression of the magnetic order and closing of the magnon gap. These results support the scenario with a significant role of the ‘extra’ spins for stabilization of the magnetic order in this frustrated quantum magnet.