Nonlinear interactions of longitudinal acoustic modes in magnets near the antiferromagnetic-ferromagnetic phase transition

The effective elastic anharmonicity induced by exchange magnetoelastic interaction is investigated for easy plane antiferromagnets, in which an antiferromagnetic-ferromagnetic phase transition takes place. Near the transition point this anharmonicity can be manifested in nonlinear interactions of longitudinal acoustic modes, resulting in magnetoacoustic mode-frequency conversion effects. It is shown that these effects are amplified in the vicinity of the phase transition, because the effective third-order elastic constants increase by several orders of magnitude. The generation of longitudinal acoustic second harmonics is analyzed as an example.