Ultrasonic study of structural instabilities in nickel induced by magnetic fields

Abstract

The ultrasonic phase velocity was measured on a high purity nickel single crystal with a bias magnetic field in cooling and heating runs over the interval of temperatures from approximately 100 to 325 K. An evident anomaly of the phase velocity was observed in both branches of the temperature cycle. The temperature of the anomaly in the heating run was always greater than that in the cooling run, indicating the presence of a hysteretic mechanism. The observed changes are attributed to dimensional alignment of the nickel single crystal twins which are able to distort the crystalline network. The temperature of the anomalies and its hysteretic behavior depend on the synergy between the direction and strength of the magnetic field, the direction of the ultrasonic wave propagation, the internal friction between the domains and the crystallographic orientation. The frictions between magnetic domains that do not contribute to the velocity anomaly produce a hysteretic loop. The process can be easily inhibited by disorientation of the magnetic field.

Polar orientation and extension in a novel crystallographic model for PbTiO3-based perovskites explaining the experimental ferroelectric thermal anomalies

“…The Pb 0.55 Ca 0.45 TiO 3 sample was prepared in a cylindrical geometry, 10 mm in diameter and height. The measurement faces were carefully mechanically polished until good parallelism was achieved, as described in previous reports (Moreno-Gobbi et al, 2008;Favre et al, 2012). Ultrasonic velocity and attenuation were simultaneously measured using the conventional pulse-echo method (Truell et al, 1969).…”