arXiv subjects

Ratnamala Chatterjee

Publications and source records attributed to Ratnamala Chatterjee.

14 recordsLinked to original sources

arXiv2026

A low-temperature setup for lock-in technique based dynamic magnetoelectric coupling measurements

Magnetoelectric (ME) phenomena in emerging material classes, such as two-dimensional van der Waals (vdW) magnets and Single-Molecule Magnets (SMMs), hold immense promise for next-generation cryogenic memory and quantum technologies. However, ME coupling in these systems predominantly manifests at low temperatures, making a sensitive, cryo-compatible ME characterization techniques critical. To address this requirement, we report the design, validation, and performance of a custom closed-cycle refrigerator-based setup for dynamic lock-in ME coupling measurements across 20-300 K under dc magnetic fields up to 7.5 kOe. Key design considerations for mitigating parasitic inductive background signals are also presented. The setup was validated on a CoFe2O4-BaTiO3 (CFO-BTO) particulate composite, reproducing the characteristic room-temperature butterfly ME loop with a maximum ME coefficient value of 0.23 mV/cm-Oe at ~ 3 kOe. Temperature-dependent measurements resolved ME anomalies at ~ 200 K and 280 K, coinciding with the rhombohedral-orthorhombic and orthorhombic-tetragonal structural transitions of BaTiO3, and were corroborated by simultaneous dielectric measurements on the same sample without cryostat reconfiguration. The instrument enables reliable ME and dielectric characterization down to 20 K, making it well suited for probing weak magnetoelectric coupling and phase transitions in multiferroic composites and quantum materials.

cond-mat.mtrl-sci↗

arXiv2026

Complex field-induced magnetic phases and anisotropic magnetotransport in off-stoichiometric CeCuBi2

We report a detailed study on the structural, angle-dependent magnetic and magnetotransport properties of highly anisotropic off-stoichiometric CeCuBi2 single crystals. Our results reveal CeCuBi2 as an anisotropic Kondo antiferromagnet exhibiting complex field-induced magnetic behavior and unusual magnetotransport properties. Magnetic susceptibility and specific heat measurements reveal antiferromagnetic (AFM) ordering below TN = 14 K with strong anisotropy and weak heavy-fermion behavior. Electrical transport measurements show highly anisotropic resistivity and a broad hump around 47 K, indicative of Kondo-driven heavy-fermion behavior. Magnetization measurements reveal multiple field-induced metamagnetic phases, while AC susceptibility measurements indicate slow spin dynamics and spin-glass-like behavior in intermediate field-induced magnetic states. Furthermore, we observe large and strongly anisotropic magneto transport responses, including room-temperature magnetoresistance of approximately 22% at 300 K and 9 T and butterfly-like anisotropic magnetoresistance with AMR values reaching approximately 10.9%. These results highlight a strong interplay among Kondo correlations, magnetic anisotropy, and field-tunable spin configurations, making CeCuBi2 a possible platform for exploring correlated and anisotropic quantum phenomena.

cond-mat.str-el↗

arXiv2026

Second-harmonic signal in electric-field-modulated EPR spectra of Fe3 spin triangles

We present electric-field-modulated electron paramagnetic resonance (EFM-EPR) measurements on centrosymmetric single crystals of the molecular spin triangle $\mathrm{[{Fe_3}O({O_2}CPh){_6}(py){_3}]ClO{_4}{\cdot}py}$ ($\bf{Fe_3}$). We provide the first observation of second harmonic EFM-EPR signal in polynuclear magnetic molecules. This signal is simulated and explained in terms of an electric-field induced modulation of the isotropic exchange in the molecule, and of their symmetry lowering resulting from a Jahn-Teller effect. Additionally, an unexpected first harmonic EFM-EPR signal is observed. Various plausible symmetry-breaking mechanisms are discussed in an attempt to explain this feature, whose observation is unexpected in a nominally centrosymmetric crystal.

cond-mat.mtrl-sci↗

arXiv2023

Large thermo-spin effects in Heusler alloy based spin-gapless semiconductor thin films

Recently, Heusler alloys-based spin gapless semiconductors (SGSs) with high Curie temperature (TC) and sizeable spin polarization have emerged as potential candidates for tunable spintronic applications. We report comprehensive investigation of the temperature dependent ANE and intrinsic longitudinal spin Seebeck effect (LSSE) in CoFeCrGa thin films grown on MgO substrates. Our findings show the anomalous Nernst coefficient for the MgO/CoFeCrGa (95 nm) film is $\cong 1.86$ micro V/K at room temperature which is nearly two orders of magnitude higher than that of the bulk polycrystalline sample of CoFeCrGa (= 0.018 micro V/K) but comparable to that of the magnetic Weyl semimetal Co2MnGa thin film (2-3 micro V/K). Furthermore, the LSSE coefficient for our MgO/CoFeCrGa(95nm)/Pt(5nm) heterostructure is $\cong 20.5$ $μ$V/K/$Ω$ at room temperature which is twice larger than that of the half-metallic ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_3$ thin films ($\cong$ 20.5 $μ$V/K/$Ω$). We show that both ANE and LSSE coefficients follow identical temperature dependences and exhibit a maximum at $\cong$ 225 K which is understood as the combined effects of inelastic magnon scatterings and reduced magnon population at low temperatures. Our analyses not only indicate that the extrinsic skew scattering is the dominating mechanism for ANE in these films but also provide critical insights into the functional form of the observed temperature dependent LSSE at low temperatures. Furthermore, by employing radio frequency transverse susceptibility and broadband ferromagnetic resonance in combination with the LSSE measurements, we establish a correlation among the observed LSSE signal, magnetic anisotropy and Gilbert damping of the CoFeCrGa thin films, which will be beneficial for fabricating tunable and highly efficient Heusler alloys based spincaloritronic nanodevices.

physics.app-ph↗

arXiv2022

Machine learning approach to genome of two-dimensional materials with flat electronic bands

Many-body physics of electron-electron correlations plays a central role in condensed mater physics, it governs a wide range of phenomena, stretching from superconductivity to magnetism, and is behind numerous technological applications. To explore this rich interaction-driven physics, two-dimensional (2D) materials with flat electronic bands provide a natural playground thanks to their highly localised electrons. Currently, thousands of 2D materials with computed electronic bands are available in open science databases, awaiting such exploration. Here we used a new machine learning algorithm combining both supervised and unsupervised machine intelligence to automate the otherwise daunting task of materials search and classification, to build a genome of 2D materials hosting flat electronic bands. To this end, a feedforward artificial neural network was employed to identify 2D flat band materials, which were then classified by a bilayer unsupervised learning algorithm. Such a hybrid approach of exploring materials databases allowed us to reveal completely new material classes outside the known flat band paradigms, offering new systems for in-depth study on their electronic interactions.

cond-mat.mes-hall↗

arXiv2022

A new poling protocol for enhanced piezoelectricity in Bi0.5Na0.5TiO3

In this work, a way to improve the piezoelectric properties of Bi0.5Na0.5TiO3 (BNT) is demonstrated by introducing a new poling protocol. A customized corona poling unit with a low temperature (77 K) sample stage is suggested. Using this protocol, the BNT sample is quenched from its paraelectric phase (T = 350°C) directly to its ferroelectric phase under corona discharge. Sample poled under this protocol showed an immense improvement (~38% increase) in the piezoelectric coefficient (d33) and 20% increase in the maximum unipolar piezoelectric strain (Smax).

cond-mat.mtrl-sci↗

arXiv2021

Structural and transport properties of 4f electron doped Y1-x(Dy)xPdBi topological semi-metallic thin films

We report the effect of 4f electron doping on structural, electrical and magneto-transport properties of Dy doped half Heusler Y1-x(Dy)xPdBi (x =0, 0.2, 0.5, 1) thin films grown by pulsed laser deposition. The Dy doping leads to lattice contraction which increases from 0% for the parent x =0 sample to approx 1.3% for x=1 sample with increase in Dy doping. The electrical transport measurements show a typical semi-metallic behaviour in the temperature range 3K to 300K and a sharp drop in resistivity at low temperatures (less than 3K) for all the samples. Magnetotransport measurements and Shubnikov de-Hass oscillations at high magnetic fields demonstrate that for these topologically non-trivial samples, Dy doping induced lattice contraction plays an active role in modifying the Fermi surface, carrier concentration and the effective electron mass. There is an uniform suppression of the onset of superconductivity with increased Dy doping which is possibly related to the increasing local exchange field arising from the 4f electrons in Dy. Our results indicate that we can tune various band structure parameters of YPdBi by f electron doping and strained thin films of Y1-x(Dy)xPdBi show surface dominated relativistic carrier transport at low temperatures.

cond-mat.mtrl-sci↗

arXiv2021

Strain driven emergence of topological non-triviality in YPdBi thin films

Half-Heusler compounds exhibit a remarkable variety of emergent properties such as heavy-fermion behaviour, unconventional superconductivity and magnetism. Several of these compounds have been predicted to host topologically non-trivial electronic structures. Remarkably, recent theoretical studies have indicated the possibility to induce non-trivial topological surface states in an otherwise trivial half-Heusler system by strain engineering. Here, using magneto-transport measurements and first principles DFT-based simulations, we demonstrate topological surface states on strained [110] oriented thin films of YPdBi grown on (100) MgO. These topological surface states arise in an otherwise trivial semi-metal purely driven by strain. Furthermore, we observe the onset of superconductivity in these strained films highlighting the possibility of engineering a topological superconducting state. Our results demonstrate the critical role played by strain in engineering novel topological states in thin film systems for developing next-generation spintronic devices.

cond-mat.mtrl-sci↗

arXiv2020

New quantum phases of matter: Topological Materials

In this article, we provide an overview of the basic concepts of novel topological materials. This new class of materials developed by combining the Weyl/Dirac fermionic electron states and magnetism, provide a materials-science platform to test predictions of the laws of topological physics. Owing to their dissipationless transport, these materials hold high promises for technological applications in quantum computing and spintronics devices.

cond-mat.mes-hall↗

arXiv2017

Effect of nanostructure on thermoelectric properties of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ in 300-600 K range

In oxide materials, nanostructuring effect has been found very promising approach for the enhancement of \textit{figure-of-merit}, \textit{ZT}. In the present work, we have synthesized La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) compound using sol-gel method and samples of crystallite size of 34, 41, and 49 nm were obtained by giving different heat treatment. Seebeck coefficient ($α$), electrical resistivity ($ρ$), and thermal conductivity ($κ$) measurements were carried out in 300-600 K temperature range. The systematic change in the values of $α$ from $\sim$ -19 $μ$V/K to $\sim$ -24 $μ$V/K and drastic reduction in the values of $κ$ from $\sim$0.88 W/mK to $\sim$0.23 W/mK are observed as crystallite size is reduced from 49 nm to 34 nm at $\sim$600 K. Also, fall in the values of $ρ$ in the paramagnetic (PM) insulator phase (400-600 K) are effectively responsible for the increasing trend in the values of \textit{ZT} at high temperature. For the crystallite size of 41 nm, value of \textit{ZT} at 600 K was found to be $\sim$0.017, which can be further increased up to $\sim$0.045 around 650 K temperature. The predicted value of \textit{ZT} suggests that LSMO can be suitable oxide material for thermoelectric applications at high temperature.

physics.app-ph↗

arXiv2015

Investigation of Arrott plot and magnetocaloric effect in the complex CaMn7O12 perovskite

Detailed magnetic studies including magneto-caloric measurements on magnetic multiferroic quadruple perovskite CaMn7O12 are presented. Based on the collective response of Arrott plots and ΔSM (T), a magnetic phase diagram of CaMn7O12 is suggested. A new magnetic transition at TN3 ~20 K where the system changes from noncollinear AFM to collinear AFM is reported. An anomaly observed in both ΔSM (T) and Arrott plots around 64 K has been attributed to high external field induced spin canting leading to change in magnetic order inducing phase transition. Magneto-caloric effect in this material is presented for the first time. The peak value of change in isothermal magnetic entropy is 1.3 J/K-Kg and the value of refrigeration capacity is reported to be 34.5 J/Kg for the field of 7 T.

cond-mat.mtrl-sci↗

arXiv2014

Temperature dependent Raman study of phonons of different symmetries in single crystal Bi2Se3

High quality single crystals of Bi2Se3 were grown using a modified Bridgman technique, the detailed study were carried out using Raman spectroscopy and characterized by Laue diffraction and high resolution transmission electron microscopy. Polarized Raman scattering measurements were also carried out, and both the A1g and A2g phonon modes showed strong polarization effect, which is consistent with the theoretical prediction. The temperature dependent study (in the temperature range 83 K to 523 K of Raman active modes were reported and observed to follow a systematic red shift. The frequency of these phonon modes are found to vary linearly with temperature and can be explained by first order temperature co-efficient. The temperature co-efficient for A11g, E2g and A21g modes were estimated to be -1.44*10-2, -1.94*10-2 and -1.95*10-2cm-1/K respectively.

cond-mat.mtrl-sci↗

arXiv2013

Understanding the metamagnetic transition and magnetic behavior of Ni48Co6Mn26Al20 polycrystalline ribbons

In this work we demonstrate that the polycrystalline ribbons of (Ni48Co6)Mn26Al20 with B2 structure at room temperature show a magnetic behavior with competing magnetic exchange interactions leading to frozen disorders at low temperatures. It is established that by considering the presence of both antiferromagnetic and ferromagnetic sublattices, we can explain the observed magnetic behavior including the metamagnetic transition observed in these samples. From the Arrott plots, the Néel temperature of (Ni48Co6)Mn26Al20 is deduced to be ~170 K and the broad ferro to para like magnetic phase transition is observed at ~ 200 K. Based on Néel theory, a cluster model is used to explain the presence of ferromagnetic and anti-ferromagnetic clusters in the studied ribbons. Formation of ferromagnetic clusters can be understood in terms of positive exchange interactions among the Mn atoms that are neighboring to Co atoms which are located on the Ni sites.

cond-mat.mtrl-sci↗

arXiv2010

Origin of Large Dielectric Constant with Large Remnant Polarization and Evidence of Magnetoelectric Coupling in Multiferroic La modified BiFeO3-PbTiO3 Solid Solution

The presence of superlattice reflections and detailed analyses of the powder neutron and x-ray diffraction data reveal that La rich (BF$_{0.50}$-LF$_{0.50}$)$_{0.50}$-(PT)$_{0.50}$ (BF-LF-PT) has ferroelectric rhombohedral crystal structure with space group \textit{$R3c$} at ambient conditions. The temperature dependence of lattice parameters, tilt angle, calculated polarization $(P_{s})$, volume, and integrated intensity of superlattice and magnetic reflections show an anomaly around 170 K. Impedance spectroscopy, dielectric and ac conductivity measurements were performed in temperature range $473K \leq T \leq 573K$ to probe the origin of large remnant polarization and frequency dependent broad transitions with large dielectric constant near $T_c^{FE}$. Results of impedance spectroscopy measurements clearly show contributions of both grain and grain boundaries throughout the frequency range ($10^{3}$ Hz$\leq f\leq 10^{7} $ Hz). It could be concluded that the grain boundaries are more resistive and capacitive as compared to the grains, resulting in inhomogeneities in the sample causing broad frequency dependent dielectric anomalies. Enhancement in dielectric constant and remnant polarization values are possibly due to space charge polarization caused by piling of charges at the interface of grains and grain boundaries. The imaginary parts of dielectric constant ($ε^{\prime\prime}$) Vs frequency data were fitted using Maxwell-Wagner model at $T_c^{FE}(\sim 523$K) and model fits very well with the data up to $10^{5}$ Hz. Magnetodielectric measurements prove that the sample starts exhibiting magnetoelectric coupling at $\sim 170$ K, which is also validated by neutron diffraction data.

cond-mat.mtrl-sci↗