Events

Interdisciplinary Seminar of International Laboratory of High Magnetic Fields and Low Temperatures PAS

Multiferroic Sr_1-xBa_xMnO₃ Perovskite with a Huge Magnetoelectric Coupling

Prof. Bogdan Dabrowski

Department of Physics, Northern Illinois University, DeKalb, USA

We have prepared unique multiferroic Sr²⁺_1-xBa²⁺_xMn⁴⁺O₃ perovskite ceramics (x=0.4-0.45), for which ferroelectricity (T_F~400K) and antiferromagnetism (T_N~200K) originate exclusively from the Mn cations. Similar to Ba²⁺Ti⁴⁺O₃, the classical displacive-type ferroelectric phase transition occurs for x>0.4, when the Mn ions move out of the center of the MnO₆ octahedral units. Upon cooling, these materials show a sequence of phase transitions: from the paramagnetic and paraelectric cubic phase to the paramagnetic and ferroelectric tetragonal P4mm phase and finally to the antiferromagnetic, and paraelectric P4/mmm phase. The largest known magneto-electric coupling has been observed near T_N, when ferroelectricity disappears. Because of high conductivity, the measurements of complex dielectric permittivity are reliable only below 40 K, where intrinsic permittivity is about 340 and does not change with magnetic field up to 9T. The antiferromagnetic order parameter has an energy gap of 4.6(5) meV and the top of the magnon band at 43(1) meV. Nearest-neighbor exchange modeling indicates exchange constant of J=4.8(2) meV.