Spin dynamics of quasi-two-dimensional Heisenberg antiferromagnetic Eu2CuO4

Uniform (with wave vector q=0) well defined (with damping γ<<ω0) excitation spectra with ω0 frequency in wide temperature range, including temperatures, exceeding Neel one TN, were revealed in dielectric crystal Eu2CuO4 in SHF range of electromagnetic waves. Antiferromagnetic resonance was observed in critical region, when two-dimensional antiferromagnetic spin fluctuations with large correlation radius ξ were observed in the crystal. Existence of well defined uniform spin excitations in quasi-two-dimensional Heinsenberg antiferromagnetic materials is possible, if strong anisotropy of a certain symmetry is taken into account. Particular mechanisms of anisotropy are discussed for Eu2CuO4 crystals. Phase state diagram was constructed. 19 refs.; 6 figs