Magnetoelastic standing waves induced in UO2 by microsecond magnetic field pulses

Magnetoelastic dilatometry of the piezomagnetic antiferromagnet UO2 was 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 microsecond timescales, pulsed-magnetic fields excite mechanical resonances at temperatures ranging from 10 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-µs observation window, are attributed to the strong magnetoelastic coupling in UO2 combined with the high crystalline quality of the single crystal samples. They compare well with mechanical resonances obtained by a resonant ultrasound technique and superimpose on the known nonmonotonic magnetostriction background. A clear phase shift of π in the lattice oscillations is observed in the antiferromagnetic state when the magnetic field overcomes the piezomagnetic switch field Hc=−18 T. We present a theoretical argument that explains this unexpected behavior as a result of the reversal of the antiferromagnetic order parameter at Hc.

Resonant Ultrasound Spectroscopy: Sensitivity Analysis for Anisotropic Materials with Hexagonal Symmetry

Resonance ultrasound spectroscopy (RUS) is a non-destructive technique for evaluating elastic and an-elastic material properties. The frequencies of free vibrations for a carefully crafted sample are measured, and material properties can be extracted from this. In one popular application, the determination of monocrystal elasticity, the results are not always reliable. In some cases, the resonant frequencies are insensitive to changes in certain elastic constants or their linear combinations. Previous work has been done to characterize these sensitivity issues in materials with isotropic and cubic symmetry. This work examines the sensitivity of elastic constant measurements by the RUS method for materials with hexagonal symmetry, such as titanium-diboride. We investigate the reliability of RUS data and explore supplemental measurements to obtain an accurate and complete set of elastic constants.

Resonant ultrasound spectroscopy of silicon carbide ceramics SiC‒AlN

The paper discusses the possibility of using resonant ultrasonic spectroscopy (RUS) as a source of information for the physics and technology of obtaining silicon carbide ceramics by the example of samples of the composition SiC ‒ 25 % AlN, obtained by the method of spark plasma sintering. The possibility of obtaining a complete set of elastic moduli (EM) of samples with an error of less than 1 % is shown. At the same time, the requirements for surface quality are significantly reduced. The revealed functional relationship between EM and porosity makes it possible to create a non-destructive method of porosity control and calculate the elastic moduli at zero porosity (i. e., the elastic modulus of the ceramic matrix EM0). Comparison of EM0 samples obtained at different parameters of the technological process allows determining their optima values..