arXiv subjects

Ujjal Chowdhury

Publications and source records attributed to Ujjal Chowdhury.

4 recordsLinked to original sources

arXiv2019

Origin of Ferroelectricity in Orthorhombic LuFeO$_3$

We demonstrate that small but finite ferroelectric polarization ($\sim$0.01 $μ$C/cm$^2$) emerges in orthorhombic LuFeO$_3$ ($Pnma$) at $T_N$ ($\sim$600 K) because of commensurate (k = 0) and collinear magnetic structure. The synchrotron x-ray and neutron diffraction data suggest that the polarization could originate from enhanced bond covalency together with subtle contribution from lattice. The theoretical calculations indicate enhancement of bond covalency as well as the possibility of structural transition to the polar $Pna2_1$ phase below $T_N$. The $Pna2_1$ phase, in fact, is found to be energetically favorable below $T_N$ in orthorhombic LuFeO$_3$ ($albeit$ with very small energy difference) than in isostructural and nonferroelectric LaFeO$_3$ or NdFeO$_3$. Application of electric field induces finite piezostriction in LuFeO$_3$ via electrostriction resulting in clear domain contrast images in piezoresponse force microscopy.

cond-mat.str-el↗

arXiv2016

Determination of intrinsic ferroelectric polarization in lossy improper ferroelectric systems

We measured the intrinsic hysteretic polarization in lossy improper and nanoferroelectric systems where the nonhysteretic polarization and leakage are large and the relaxation takes place over a broader time scale. We used different measurement protocols such as standard single triangular voltage pulse, a pulse train of PUND (Positive Up Negative Down), and an even more complicated pulse train of fourteen voltage pulses and compared the results obtained. We show that a protocol which sends a train of fourteen pulses is more appropriate for extracting relaxed (i.e., time scale independent) and intrinsic remanent polarization for these samples. We also point out that it is possible to select and design an appropriate measurement protocol depending on the magnitude of polarization and leakage of the system.

cond-mat.str-el↗

arXiv2014

Room temperature multiferroicity in orthorhombic LuFeO$_3$

From the measurement of dielectric, ferroelectric, and magnetic properties we observe simultaneous ferroelectric and magnetic transitions around $\sim$600 K in orthorhombic LuFeO$_3$. We also observe suppression of the remanent polarization by $\sim$95\% under a magnetic field of $\sim$15 kOe at room temperature. The extent of suppression of the polarization under magnetic field increases monotonically with the field. These results show that even the orthorhombic LuFeO$_3$ is a room temperature multiferroic of type-II variety exhibiting quite a strong coupling between magnetization and polarization.

cond-mat.str-el↗

arXiv2013

Large magnetocapacitance in electronic ferroelectric manganite systems

We have observed a sizable positive magnetocapacitance ($\sim$$5-90\%$) in perovskite Pr$_{0.55}$Ca$_{0.45}$MnO$_3$ and bilayer Pr(Sr$_{0.1}$Ca$_{0.9}$)$_2$Mn$_2$O$_7$ system under 5T magnetic field across 20-100 K below the magnetic transition point T$_N$. The magnetodielectric effect, on the other hand, exhibits a crossover: (a) from positive to negative for the perovskite system and (b) from negative to positive for the bilayer system over the same temperature range. The bilayer Pr(Sr$_{0.1}$Ca$_{0.9}$)$_2$Mn$_2$O$_7$ system exhibits a sizable anisotropy as well. We have also noticed the influence of magnetic field on the dielectric relaxation characteristics of these systems. These systems belong to a class of improper ferroelectrics and are expected to exhibit charge/orbital order driven ferroelectric polarization below the transition point T$_{CO}$. Large magnetocapacitance in these systems shows typical multiferroic behavior even though the ferroelectric polarization is small in comparison to that of other ferroelectrics.

cond-mat.str-el↗