arXiv subjects

Devajyoti Mukherjee

Publications and source records attributed to Devajyoti Mukherjee.

6 recordsLinked to original sources

arXiv2026

Negative thermal expansion, lattice dynamics, and complex magnetism in TbFeO$_3$

We report a temperature-dependent investigation of orthoferrite TbFeO$_3$ using x-ray diffraction, DC magnetization, and Raman scattering, complemented by room-temperature x-ray photoelectron spectroscopy. X-ray diffraction reveals negative thermal expansion over 5-300 K, with a small but systematic increase in unit-cell volume upon cooling in the absence of any structural phase transition. Raman scattering measurements identify the Raman-active phonon modes and show clear deviations from the conventional Klemens anharmonic decay model, particularly in phonon frequencies, indicating the presence of spin-phonon coupling. Two modes of $A_g$ and $B_{1g}$ symmetry exhibit a crossover from Gaussian-dominated line shapes at low temperatures to mixed Gaussian-Lorentzian profiles at higher temperatures, reflecting a transition from inhomogeneous broadening to lifetime-driven dynamics. High-energy Raman spectra reveal two-magnon excitations associated with the Fe sublattice, consistent with linear spin-wave theory, whose spectral weight shows only weak temperature dependence. In addition, a broad Raman mode emerging below $\sim 175$ K exhibits an order-parameter-like temperature evolution and coincides with the onset of phonon anomalies, while no corresponding strong anomaly is observed in the two-magnon response. Taken together, these results establish TbFeO$_3$ as a system with pronounced interplay among lattice dynamics, spin correlations, and emergent local magnetic-lattice anomalies.

cond-mat.str-el↗

arXiv2026

Room-Temperature Electric-Field Control of Anomalous Hall Effect in Py/BTO/LSMO Heterostructures

We demonstrate room temperature electric field control of the anomalous Hall effect in epitaxial Ni80Fe20 (Py) BaTiO3 (BTO) La0.7Sr0.3MnO3 (LSMO) thin film heterostructures grown on MgO and LaAlO3 substrates. Substrate induced strain states generate distinct magnetic anisotropies, enabling voltage driven tuning between anomalous and topological Hall contributions. Robust ferroelectric polarization in BTO, confirmed by piezoresponse force microscopy, couples strongly to interfacial orbital reconstruction and carrier redistribution. As a result, Hall resistivity exhibits giant low voltage tunability, with up to nearly 93 percent modulation at operating voltages of only 0.5 tand 2 V. Density functional theory calculations further reveal polarization controlled Rashba spin splitting, establishing a direct link between ferroelectric order and emergent quantum transport. These findings establish Py/BTO/LSMO heterostructures as promising candidates for low-power multifunctional spintronic devices, where substrate engineering enables control over emergent quantum transport phenomena.

cond-mat.mtrl-sci↗

arXiv2026

Interface engineering of the anomalous Hall effect in Ni-based heterostructures

Using a combined experimental and first-principles theoretical approach, we demonstrate interface engineering of the anomalous Hall effect in Ni-based epitaxial thin-film heterostructures. Ferromagnetic Ni thin films are grown on (001)-oriented single-crystal LaAlO$_3$, SrTiO$_3$, and MgO substrates, which impose different biaxial tensile strains of 0.3%, 0.6%, and 0.8%, respectively. Our room-temperature Hall transport measurements reveal a pronounced substrate-dependent modulation of the anomalous Hall conductivity. Interestingly, our calculations show that strain alone cannot account for the experimentally observed trends. Instead, we identify interfacial inversion-symmetry breaking, which induces Rashba spin-orbit interaction, as the key mechanism governing the anomalous Hall conductivity across different interfaces. Building on this understanding, we further demonstrate both theoretically and experimentally that the anomalous Hall conductivity can be continuously tuned by an external electric field. These findings establish the critical role of substrate-induced interfacial effects in controlling the anomalous Hall effect in engineered heterostructures and provide a viable pathway toward electrically tunable room-temperature spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Enhanced negative capacitance in La-doped Pb(Zr$_{0.4}$Ti$_{0.6}$)O$_3$ ferroelectric capacitor from tuning of bias voltage pulse

We report a remarkable bias voltage dependent specific negative capacitance in multidomain La-doped Pb(Zr$_{0.4}$Ti$_{0.6}$)O$_3$ (PLZT) ferroelectric capacitors. The specific negative capacitance maximizes at a specific bias voltage because of emergence of maximum domain-wall density during ``switching" of the domains. Domain configuration changes from such an ``optimum" state if higher or lower bias voltage is applied at a much faster or slower rate. Phase-field simulation using time-dependent Ginzburg-Landau equation corroborates the experimental results and shows dependence of the domain-wall length during switching on the bias voltage amplitude and its maximization at a specific bias voltage amplitude. Interestingly, the radius of curvature of the resulting polarization ($P$) versus voltage ($V$) hysteresis loop at the coercive voltage ($V_C$), as well, turns out to be depending on the bias voltage. All these results indicate a close correlation among the bias voltage pulse profile (amplitude and time scale), domain-wall length during switching, shape of the resulting ferroelectric hysteresis loop, and the transient negative capacitance. It may have important ramifications both in the context of physics behind negative capacitance in a multidomain ferroelectric capacitor and devices being developed by exploiting its advantages.

cond-mat.mtrl-sci↗

arXiv2025

Giant topological Hall effect in epitaxial Ni$_{80}$Fe$_{20}$/La$_{0.65}$Sr$_{0.35}$MnO$_3$ thin film heterostructures

The emergence of new physical properties at the interfaces between complex oxides has always been of both fundamental and practical importance. Here, we report the observation of a giant topological Hall resistivity of $\sim 2.8 \mu \Omega$ \text{cm} at room temperature in an epitaxial thin-film heterostructure of permalloy (Py, Ni$_{80}$Fe$_{20}$) and the half-metallic ferromagnet La$_{0.65}$Sr$_{0.35}$MnO$_3$ (LSMO). This large magnitude of the topological Hall effect in the Py/LSMO heterostructure, compared to a single-layer Py thin film, is attributed to the optimized combination of ferromagnetism in LSMO and the strong spin-orbit-coupling-driven Rashba interaction at the interface. The introduction of a ferroelectric BaTiO$_3$ (BTO) sandwich layer in the Py/LSMO heterostructure also leads to an enhanced topological Hall resistivity compared to the single-layer Py thin film. Interestingly, magnetic force microscopy measurements reveal skyrmion-like features, suggesting the origin of the topological Hall effect. Our theoretical model calculations for the skyrmion lattice further indicate that the Rashba interaction, driven by the broken inversion symmetry in the Py/LSMO films, can account for the observed changes in the topological Hall effect at the interface. Our work opens the door for the potential use of Py/LSMO thin films in spintronic applications.

cond-mat.mtrl-sci↗

arXiv2024

Evidence of spin reorientation transition below 150 K from magnetic force microscopy in a ferromagnetic BiFeO$_3$ thin film

We investigated the magnetic transitions in BiFeO$_3$ at low temperature (5-300 K) and observed nearly 90$^o$ rotation of magnetic domains (imaged by vertical magnetic force microscopy) across 150 K in an epitaxial thin film of thickness $\sim$36 nm. It offers a clear evidence of spin reorientation transition. It also corroborates the transition observed below $\sim$150 K in the zero-field-cooled and field-cooled magnetization versus temperature data. The field-driven 180$^o$ domain switching at room temperature, on the other hand, signifies presence of ferromagnetism. Since bulk antiferromagnetic BiFeO$_3$ does not exhibit such a transition, this observation in ferromagnetic thin film of BiFeO$_3$ indicates a radical effect because of epitaxial strain. Density functional theory based first-principles calculations too reveal that combined in- and out-of-plane epitaxial strain induces magnetic transition from G- to C-type structure in BiFeO$_3$.

cond-mat.mtrl-sci↗