Investigation of multiferroic magnetic systems by ultrasonic velocity measurements

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We are principally interested in the study of multiferroic compounds which are simultaneously antiferromagnetic, ferroelectric, and ferroelastic. Besides the fundamental scientific interest, this class of magnetoelectric materials (materials that show a coupling between their magnetic and ferroelectric properties) can potentially be used as an alternative means for controlling the magnetization in future electronic memory devices, as well as for actuators, switches, and magnetic field sensors. The interest in this field has been trigger by recent results which suggest that triangular lattice antiferromagnets, which favour non-collinear spin configuration due to magnetic frustration, are good candidates for the observation of strong magnetoelectric effects. Thus, the objective of this program of research is to investigate the magnetic, ferroelectric, and elastic properties of a series of frustrated multiferroic compounds which display ferroelectricity induced upon the stabilization of a helical magnetic structure at low or even high temperatures in the case of CuO (T = 230 K) and BiFeO3 (T = 643 K). The fundamental elastic properties of this class of materials are accessed using high resolution ultrasonic velocity measurements. Our laboratory offers a flexible way to investigate the elastic properties of single crystals under hydraulic pressure as a function of temperature and magnetic field. We are one of the few groups in the world capable of measuring elastic properties and phase diagrams as a function of these three external parameters over a wide range (2 - 300 K, 0 - 15 Tesla, and 0 - 15 kbar). Our approach holds potential for the acquisition of significant results in order to clarify the nature of the coupling between elastic, electric, and magnetic properties observed in this family of compounds. These results will also provide guidance for theoretical models developed by our group. This work should therefore contribute to a better understanding of the properties of magnetoelectric compounds and could lead to the development of new materials for technological applications.