Suryakanta Mishra | Searcharxiv

arXiv2026

Antisite-disorder driven tuning of magnetic properties and exchange-bias in Nd$_{2-x}$Sr$_{x}$CoMnO$_{6-δ}$ $(0 \leq x \leq 1)$ ($δ\sim 0.5$) double perovskites

We demonstrate precise control of exchange bias (EB) in the Nd$_{2-x}$Sr$_x$CoMnO$_{6-δ}$ ($0 \leq x \leq 1$) double-perovskite series through Sr$^{2+}$ induced hole doping, unveiling a remarkable transition between normal and inverse EB states. Employing neutron powder diffraction and X-ray absorption spectroscopy, we reveal a structural evolution from a B-site-ordered monoclinic ($P2_1/n$) phase to a disordered rhombohedral ($R\overline{3}c$) phase with increasing $x$, accompanied by a shift in the effective Co valence from +2 toward +3, while the Mn valence remains essentially unchanged. DC magnetization measurements indicate a gradual suppression of ferromagnetism with hole doping, whereas AC susceptibility measurements at $x = 0.75$ reveal pronounced cluster-glass behavior and the highest EB field of $\sim 4$ kOe at 8 K under a 6 T cooling field. After correcting for minor-loop effects, we identify robust inverse EB at $x = 0.75$, persisting even under a cooling field of 6 T. We attribute this phenomenon to competing ferromagnetic--antiferromagnetic and ferromagnetic--glassy interfaces, governed by strong magnetic frustration and the magnetocrystalline anisotropy associated with rare-earth 4$f$ electrons. These findings elucidate the pivotal role of doping-induced structural and magnetic competition in tailoring EB behavior in rare-earth double perovskites, providing new insights for the design of advanced magnetic materials.

cond-mat.str-el↗

arXiv2023

Emergent room-temperature ferroelectricity in spark-plasma sintered DyCrO$_3$ and LaCrO$_3$

Identification of novel multiferroic materials with high-ordering temperatures remains at the forefront of condensed matter physics research. In this regard, the antiferromagnetic RCrO$_3$ compounds (like GdCrO$_3$) constitute a promising class of multiferroic compounds, which, however, mostly become ferroelectric concomitant with the antiferromagnetic ordering much below room-temperature, arising from a subtle competition between the ferroelectric off-centering mode and a non-polar antiferrodistortive rotation mode that inhibits ferroelectricity. Recently, room-temperature ferroelectricity of structural origin, arising from off-centering displacements of R and Cr ions, has been identified in spark-plasma sintered GdCrO$_3$ [Suryakanta Mishra et al., Phys. Rev. B 104, L180101 (2021)]. Interestingly, some of the experimentally observed non-ferroelectric RCrO$_3$ compounds have been theoretically predicted to host similar ferroelectric instabilities. Here, we have identified two such non-ferroelectric RCrO3 compounds, one DyCrO$_3$ (which is reported as a quantum paraelectric) and another LaCrO$_3$ (which is paraelectric), and using a modified synthesis protocol involving spark-plasma-sintering (SPS), we have been successful in engineering an intrinsic room-temperature ferroelectricity in the paramagnetic state, driven by noncentrosymmetric structural phase in both SPS sintered DyCrO$_3$ and LaCrO$_3$, in contrast to room-temperature paraelectricity in solid-state synthesized DyCrO$_3$ and LaCrO$_3$. While the ferroelectricity in SPS-prepared DyCrO$_3$ and LaCrO$_3$ is stable at room-temperature, it undergoes an irreversible transition from a ferroelectric (Pna2$_1$) phase to a paraelectric (Pbnm) phase at 440 K. Significantly, SPS-sintered LaCrO$_3$, which undergoes antiferromagnetic ordering at 290 K, emerges as a promising near room-temperature multiferroic material.

cond-mat.mtrl-sci↗