Paramagnetic and antiferromagnetic resonances in the diamagnetically diluted Haldane magnet PbNi2V2O8

Abstract

The impurity-induced antiferromagnetic ordering of the doped Haldane magnet Pb(Nil-xMgx)2V2O8 (0 ≤x≤0.06) was studied by electron-spin resonance (ESR) on ceramic samples in the frequency range 9-110 GHz. Below the Néel temperature a transformation of the ESR spectrum was found, indicating an antiferromagnetic-resonance mode of spin precession. The excitation gap of the spin-wave spectrum increases with increasing Mg concentration x in the same manner as the Néel temperature, reaching its maximum value of 80 GHz at x≥0.04. At small concentrations x<0.02 the signals of antiferromagnetic resonance were found to coexist with the signal of the paramagnetic resonance indicating a microscopic separation of the magnetic phases.