arXiv subjects

Ravi Kiran Dokala

Publications and source records attributed to Ravi Kiran Dokala.

4 recordsLinked to original sources

arXiv2026

Varying A-site radius and size disorder to tune magnetic ordering in compositionally complex perovskite oxides

A long standing goal of magnetochemists is to be able to control ordering temperatures through compositional engineering. Here we report the synthesis of a perovskite oxide with twelve cations accommodated within a single phase solid solution, AM7O$_3$, A = La$_{\frac{1}{5}}$Sm$_{\frac{1}{5}}$Gd$_{\frac{1}{5}}$Nd$_{\frac{1}{5}}$Dy$_{\frac{1}{5}}$ (A5), and M7 = Ti$_{\frac{1}{7}}$Cr$_{\frac{1}{7}}$Mn$_{\frac{1}{7}}$Fe$_{\frac{1}{7}}$Co$_{\frac{1}{7}}$Ni$_{\frac{1}{7}}$Cu$_{\frac{1}{7}}$. Bulk magnetometry measurements for A5M7O$_3$, as well as for A = La, Gd and La$_{\frac{1}{2}}$Gd$_{\frac{1}{2}}$, show that all these compounds magnetically order as ferrimagnets between 89 and 115 K. We find that the magnetic properties are influenced by considering a combination of the size disorder parameter alongside the A-site cationic radii and valence electrons.

cond-mat.str-el↗

arXiv2025

Giant-Magnetocaloric effect and phonon dynamics in (GdCe)CrO$_3$

We investigate the effect of Ce$^{3+}$ substitution on the magnetic ordering and phonon dynamics of the GdCrO$_3$ orthorhombic perovskite. The Ce doped compound exhibits long-range canted antiferromagnetism with Neel transitions, T$_N$ at $\sim$ 173 K, accompanied by spin-flip, T$_{SF}$ at $\sim$ 10 K. Ce$^{3+}$ incorporation drives a modification of the spin-flip transition from the $Γ{(G_x,A_y,F_z)}$ configuration to $Γ$ inducing a reorientation of the spin axis between the (001) and (001) crystallographic planes. This spin reorientation is governed by Zeeman energy and produces pronounced field-induced irreversibility between FCC and FCW magnetization processes. The substituted compound Gd$_{0.9}$Ce$_{0.1}$CrO$_3$ (GCCO) exhibits a remarkably large magnetic entropy change, $Δ$ S $\sim$ 45-40 J/kg-K for $Δ$ H = 90-70 kOe at 3 K among the highest reported for rare-earth orthochromites. The interplay of spin-only magnetocrystalline anisotropy from Cr$^{3+}$ and spin-orbit-driven magnetic moments of Gd$^{3+}$ and Ce$^{3+}$ results in pronounced spin-phonon coupling, manifested through the A$_{1g}$(6) vibrational mode. The observed temperature-dependent spectral evolution is consistent with behaviour reported in isostructural magnetic perovskites.

cond-mat.mtrl-sci↗

arXiv2025

Spin-Reorientation Dynamics and Strong-Spin Phonon Coupling in Ce-substituted SmCrO$_3$

We report the influence of Ce$^{3+}$ substitution on the magnetic structures and phonon dynamics in SmCrO$_3$ perovskites. Magnetic landscapes are spanned by long-range canted anti-ferromagnetism, AFM with Neel temperatures $\sim$196 K accompanied by spin-reorientation transitions, T$_{SRPT}$ at 42 K. In Sm$_{0.9}$Ce$_{0.1}$CrO$_3$ (SCCO), Ce$^{3+}$ substitution at Sm$^{3+}$ sites transform the weak ferromagnetic (FM) $Γ_4$ state into robust AFM $Γ_1$ configuration through a gradual crossover. Such coexistence of magnetic spin configurations $Γ_1$(AFM) to $Γ_4$ (WFM) results in the enhanced high coercive field and a pronounced exchange bias-field, $H_{\mathrm{EB}}$ $\sim$ 2 kOe. Spin-only driven magneto-crystalline anisotropy of Cr$^{3+}$ and spin-orbit driven magnetic moment in Sm$^{3+}$, and Ce$^{3+}$ exhibits spin-phonon coupling through $A_{1g}(6)$ mode in SCCO are consistent with the temperature dependent spectral features of the isostructural magnetic systems and quite significant in SCCO which is in accordance with the higher structural distortion in SCCO. These results demonstrate that site-specific R$^{3+}$ substitution modulates lattice distortions, spin-phonon coupling, and spin-orbit interactions, offering pathways to optimize perovskites for diverse spintronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Mean field magnetism and spin frustration in a double perovskite oxide with compositional complexity

The rise of high-entropy oxides as a major functional materials design principle in recent years has prompted us to investigate how compositional disorder affects long-range magnetic ordering in double perovskite oxides. Since ferromagnetic insulators are emerging as an important platform for lossless spintronics, we consider the $RE_2$NiMnO$_6$ ($RE$ : rare-earth) family and investigate single-crystalline films of (La$_{0.4}$Nd$_{0.4}$Sm$_{0.4}$Gd$_{0.4}$Y$_{0.4}$)NiMnO$_{6}$ grown on SrTiO$_3$ (001) substrates in this work. Despite configurational disorder and high cationic size variance at the $RE$ site, the material exhibits robust ferromagnetic ordering with a Curie temperature ($T_\mathrm{c}$) of approximately 150 K. This $T_\mathrm{c}$ is consistent with the expectation based on consideration of the average ionic radii of the rare-earth ($RE$) sites in the bulk $RE_2$NiMnO$_6$. Below $T_\mathrm{c}$, Raman spectroscopy measurement finds a deviation from anharmonic behavior, where the phonon renormalization aligns with a mean-field approximation of spin-spin correlation. At lower temperature, magnetic $RE$ ions also contributed to the magnetic behavior and the system displays a reentrant spin-glass-like behavior. This study demonstrates that while a mean-field approach serves as a viable starting point for predicting the long-range transition temperature, microscopic details of the complex magnetic interactions are essential for understanding the low-temperature phase.

cond-mat.mtrl-sci↗