Electron Spin Resonance in One Dimensional Antiferromagnet KCuF₃

Abstract

Magnetic properties of one dimensional antiferromagnet KCuF 3 were investigated by electron spin resonance using microwaves of 10∼70 GHz regions in the temperature range from 1.5 to 400°K. Two types of the resonances were discriminated corresponding to two crystal modifications (a) and (d). The Néel temperatures T N for these crystals were estimated to be 40±3°K and 20±3°K, respectively in accord with the data of neutron diffractions. Above T N , the line width showed a strong temperature dependence which could not be explained theoretically. The g -values obtained are, g a =2.28±0.01 and g c =2.16±0.01 for type (a) crystal and g a =2.25±0.01 and g c =2.16±0.01 for type (d), respectively. The resonance observed below T N can be explained by an antiferromagnetic resonance of orthorhombic symmetry except the presence of an extremely short and field dependent relaxation time which gives rise to quenching of the resonance below 30 GHz. In addition to a strong anisotropy along the spin hard c -axis, small anisotropy fields of 2.4±0.5 (type (a)) and 7.2±0.5 (type (d)) Oersteds were found in the c -plane. The interchain exchange interaction was determined to be ferromagnetic.