Multiferroics where at least two primary ferroic orders are present and coupled in a single system constitute an important class of materials. They attracted special consideration as they present both intriguing fundamental physics problems and technological importance for potential multifunctional devices. Here, we present the evidence of multiferroicity and magnetoelectric (ME) coupling in -Mn2O3; a unique binary perovskite. Corresponding to the antiferromagnetic (AFM) ordering around 80K, a clear frequency independent transition is observed in the dielectric permittivity. We showed that electric polarization emerges near AFM regime that can be modulated with magnetic field. The detailed structural analysis using synchrotron radiation X-ray diffraction demonstrates the increase in structural distortion with decreasing temperature, as well as changes in the unit cell parameters and bond lengths across the ferroelectric and magnetic ordering temperatures. This observation of multiferroicity and magnetoelastic coupling in -Mn2O3 provides insights for the exploration of ME coupling in related materials.

The effect of Cr doping with nominal compositions Mn 2-x Cr x O 3 (0  x  0.10) has been undertaken to investigate its effect on structural, magnetic, dielectric and magnetoelectric properties. The Cr doping transformed the room temperature crystal structure from orthorhombic to cubic symmetry. Similar to -Mn 2 O 3 , two magnetic transitions have been observed in the Cr doped samples. The effect of Cr doping is significant on the low temperature transition i.e. the lower magnetic transition shifted towards higher temperature (25 K for pristine to 40 K for x=0.10) whereas the high temperature transition decreases slightly with increasing Cr content. A clear frequency independent transition is observed in complex dielectric measurements for all compositions around high temperature magnetic ordering. Interestingly, the magnetodielectric behaviour enhanced enormously 21% with Cr substitution as compared to pristine Mn 2 O 3 .

The effect of Sr doping in BaTiO 3 (BTO) with nominal compositions Ba 0.80 Sr 0.20 TiO 3 (BSTO) have been explored in its structural, lattice vibration, dielectric, ferroelectric and electrocaloric properties. The temperature dependent dielectric results elucidate the enhancement in dielectric constant and exhibit three frequency independent transitions around 335, 250 and 185 K which are related to different structural transitions. All these transitions occur at lower temperature as compared with pristine BTO, however; remnant electric polarization (P) of BSTO is much higher than in BTO. The value of P is  5C/cm 2 at room temperature and the maximum P 8C/cm 2 is observed at tetragonal to orthorhombic and orthorhombic to rhombohedral transitions. The electro-caloric effect shows the maximum adiabatic change in temperature T 0.24 K at cubic to tetragonal transition. The temperature dependent synchrotron X-ray diffraction and Raman results shows correlations between P, crystal structure and lattice vibrations. Our results demonstrate the enhancement in ferroelectric properties of BTO with Sr doping. The origin of the enhancement in ferroelectric property is also discussed which is related to the appearance of superlattice peak around room temperature due to TiO 6 octahedral distortion. These enhanced properties would be useful to design lead free high quality ferroelectric and piezoelectric materials.

No abstract

No abstract