Submillimeter Wave ESR Study of Magnetic Excitations in the Ising Ferromagnetic Chain CoNb2O6

Abstract

Magnetic excitations in the Ising ferromagnetic chain CoNb 2 O 6 have been studied by submillimeter wave electron spin resonance in strong transverse magnetic fields. A distinct non-linear field dependence of the resonance branches and also zero field splittings have been observed. A large residual intensity of the spin-cluster resonance was found which was caused by the strong mixing among the different n -fold spin-clusters. In addition to a series of n -fold spin-cluster excitations, we also discovered a new set of spin-cluster excitation which can be attributed to non-integer n such as n ∼1.5 or n ∼2.5 for the first time. This effect is explained by the change of the quantization axis of the system in strong transverse magnetic fields. These new aspects of spin-cluster excitation show the significant effect of transverse magnetic fields on the magnetic excitation in an Ising ferromagnetic chain.