FESHBACH RESONANCE AND EXPLOSIVE INSTABILITY OF MAGNETOELASTIC WAVES

摘要

Periodic modulation of a nonlinear material parameter is an efficient mechanism of the explosive instability in acoustics. In contrast to the conventional absolute parametric instability having the exponential development scenario, the explosive instability manifests as a singularity in the wave amplitude at some finite propagation time. Our case study concerns the explosive instability of magnetoelasic Lamb waves in a magnetic material subject to the electromagnetic modulation of the third order elastic modulus. The instability occurs due to the effect of the three-phonon coupling by means of electromagnetic field. In a general many-body problem, in particular in the problem of ultra cold atoms, it is known that particles interaction is enhanced by the Feshbach resonance. In solid-state acoustics, the resonance of Feshbach type corresponds to the nonlinear interaction of traveling elastic waves with electromagnetic pumping via an acoustic mode of discrete spectrum. This mode under the appropriate resonant conditions provides a positive feedback of the traveling waves on the pumping. The effect is predicted in an antiferromagnetic material with the "easy plane" type magnetic anisotropy. In this material, the magnetoelastic interaction induces the giant acoustic nonlinearity that can be controlled by the external magnetic field. We analyze the threshold conditions for the explosive instability and numerically simulate the explosive scenario of wave amplification over the threshold. It is shown that the explosive scenario can occur with a very low level of the incident Lamb wave amplitude comparable to the spontaneous acoustic noise. The considered mechanism of nonlinearity modulation is extendable onto systems of different physical nature and potentially applicable in acousto-electronics, electro- and hydrodynamics and in microsystems designing.