A refined theory of magnetoelastic buckling matches experiments with ferromagnetic and superparamagnetic rods.

In its simplest form the magnetoelastic buckling instability refers to the sudden bending transition of an elastic rod experiencing a uniform induction field applied at a normal angle with respect to its long axis. This fundamental physics phenomenon was initially documented in 1968, and, surprisingly, despite many refinements, a gap has always remained between the observations and the theoretical expectations. Here, we first renew the theory with a simple model based on the assumption that the magnetization follows the rod axis as soon as it bends.

Phase conjugation with a single bubble.

It is recalled how the nonlinear interaction between a gas bubble and an external extra pressure can yield phase conjugation. Using the Glauber representation, we show that the effect of the latter is formally analogous to that of a pi pulse in nuclear magnetic resonance, so that the acoustic equivalent of spin echoes may be expected in a bubble cloud. An experimental attempt to observe phase conjugation is reported in the single-bubble case.