Antiferromagnetic resonance in the multiferroic frustrate YMnO₃

Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Using THz-range FEL- and BWO-based electron spin resonance (ESR) spectroscopy techniques, the frequency-field dependence of magnetic excitations in the hexagonal multiferroic YMnO₃ in the antiferromagnetically (AFM) ordered phase has been studied. A slope of the frequency-field dependences of AFM resonance modes, ~ 0.5 cm⁻¹/T, is explaned in terms of the triangular AFM model. A gap in the excitation spectrum, ~ 42 cm−1, was observed directly. A fine structure of AFM resonance absorption observed by as is a clear signature of a finite interaction between the neighboring Mn³⁺ layers. The interplane exchange interactions constants, J₁ = -510 mK and J₂ = -350 mK, have been estimated.