Magnetoelectric measurement and analysis under cryogenic conditions
Interest into multiferroic materials have been increasing in popularity in recent years due to their many technical applications, particularly magnetoelectrics. The concept of using magnetoelectrics for low-field sensor application in the aeronautics and space industry is a novel idea but first must be studied as a function of temperature. Doing so requires a measurement system that can expose a material to either an electric field or magnetic field over a broad temperature range and be able to record the resultant property of this exposure. In this thesis, a systematic approach was taken to establishing such a system as well testing the system and taking measurements of magnetoelectric materials. First, basic instrumentation was set up in the form of large DC powered electro magnets for magnetic field exposure and lock-in amplifier for voltage measurement. Secondly, a temperature controller and vacuum pump and chamber were used for cryogenic cooling of the material sample so that measurements could be recorded as both a function of magnetic field and temperature. A custom designed and built Helmholtz coil was established for the exposure of a dynamic AC magnetic field. A magnetoelectric composite material composed of layered magnetostrictive and piezoelectric was then used to test the measurement system and the results were compared to experimental data found in literature. The data was in good agreement with literature. Subsequently, measurements were done on the effective permittivity and tan(ä) of NiFe2O4/Pb(Zr-Ti)O3/NiFe2O4 magnetoelectric sample as a function of field and temperature that demonstrated the magnetodielectric effect in the material. Lastly, the orientation dependence of the material was measured at room temperature and exhibited results that agreed with the literature.