Abstract
RMnO3 (R is rare earth) crystallizes in a hexagonal structure when the ionic radius of R is small (R=Ho-Lu, Y, Yb, Tm and Sc). In this hexagonal structure, each Mn3+ ion with S=2 is surrounded by three in-plane and two apical oxygen ions, and thus is subject to a trigonal crystal field. These MnO5 blocks are two-dimensionally connected with each other on their corners, and the triangular lattice of the Mn3+ ions is formed. Based on such a triangular lattice, these compounds experience several characteristic distortions. One is Mn trimers, which are characterized by the shift of three Mn3+ ions surrounding one oxygen ion toward the oxygen. Another one is the displacement of ions along the c axis (perpendicular to the triangular-lattice plane) causing a ferroelectric polarization. Since the ferroelectric transition temperature of these compounds is fairly high (>900 K), they have potential use for application, for example, ferroelectric gate FETs. Here, we show the dielectric anomalies at around Néel point of YMnO3 epitaxial films deposited by pulsed laser deposition method. The relationship between the magnetic structure and the dielectric properties are discussed in terms of the temperature dependences of magnetization and dielectric permittivity. Eventually, the control of ferroelectric domain switching by applying external magnetic field is presented.
