Magnetoelastic standing waves induced in UO$_{2}$ by microsecond magnetic field pulses

Abstract

Magnetoelastic measurements in the piezomagnetic antiferromagnet UO2 were performed via the fiber Bragg grating method in magnetic fields up to 150 T generated by a single-turn coil setup. We show that in short timescales, order of a few micro seconds, pulsed-magnetic fields excite mechanical resonances at temperatures ranging from 10 K to 300 K, in the paramagnetic as well as within the robust antiferromagnetic state of the material. These resonances, which are barely attenuated within the 100 ms observations, are attributed to the strong magnetoelastic coupling in UO2 combined with the high crystallographic quality of the single crystal samples. They compare well with mechanical resonances obtained by a resonant ultrasound technique and superimpose on the known non-monotonic magnetostriction background. A clear phase-shift of π in the lattice oscillations is, unexpectedly, observed in the antiferromagnetic state when the magnetic field overcomes the piezomagnetic switch-field Hc −18 T. We further present simulations and a theoretical argument to explain the observed phenomena.