Effects of Al substitution on the multiferroic properties of TbMnO 3

Abstract

The effect of a small substitution of Mn with Al in TbMnO 3 has been studied. We report results of heat capacity, magnetization, and dielectric constant studies in TbMn 1-xAl xO 3 compounds (x ≤ 0.1). Al has the same valence as substituted Mn but is nonmagnetic and its small size gives rise to microstructural strain which affects the multiferroic properties of the parent compound. Long-range antiferromagnetic ordering is observed in all compounds but the transition temperature decreases as the Al content increases. TbMn 0.95Al 0.05O 3 exhibits a ferroelectric phase transition which is absent in TbMn 0.9Al 0.1O 3. The dielectric constant of the latter compound reveals a relaxor behavior suggesting the presence of nanosize polar domains for this compound. A neutron diffraction study on a single crystal of TbMn 0.9Al 0.1O 3 reveals that Mn shows a sinusoidal incommensurate ordering down to low temperature. Tb moments exhibit an incommensurate short-range ordering but the application of a magnetic field leads to metamagnetic transitions. In particular, a field parallel to the b axis induces a commensurate long-range ordering of Tb of type C xF y. The magnetic field also affects the magnetic structure of Mn3 + moments at low temperature which develop an incommensurate cycloid ordering in the ab plane. This result suggests that dilution of a magnetic multiferroic with a small nonmagnetic atom might yield materials with a relaxor to ferroelectric transition driven by a magnetic field. © 2012 American Physical Society.