Instability of magnons in two-dimensional antiferromagnets at high magnetic fields

摘要

Spin dynamics of the square lattice Heisenberg antiferromagnet, Ba_2MnGe_2O_7, is studied by a combination of bulk measurements, neutron diffraction, and inelastic neutron-scattering techniques. Easy plane type anti-ferromagnetic order is identified at T≤4.0 K. The exchange interactions are estimated as J_1 =27.8(3) μeV and J_2 = 1.0(1) μeV, and the saturation field H_C is 9.75 T. Magnetic excitation measurements with high experimental resolution setup by triple axis neutron spectrometer reveals the instability of one magnon excitation in the field range of 0.7H_C approx