arXiv subjects

Amit Chanda

Publications and source records attributed to Amit Chanda.

14 recordsLinked to original sources

arXiv2026

Lithography-free patterning of SrTiO$_3$-based two-dimensional electron gases using direct atomic layer processing

We present a scalable and lithography-free strategy for the realization of a two-dimensional electron gas (2DEG) in TiO$_2$-patterned SrTiO$_3$ (100) via Al deposition using magnetron sputtering. A 15 nm thick TiO$_2$ layer, deposited by direct atomic layer processing, is employed to spatially define the conducting regions, enabling direct transport measurements without post-growth microfabrication. Upon Al deposition, an insulating AlO$_x$ overlayer is formed, and the region lacking the TiO$_2$ pattern leads to the creation of oxygen vacancies in SrTiO$_3$. These oxygen vacancies act as electron donors, populating the Ti 3$d$ conduction bands and giving rise to a confined 2DEG at the interface. Magneto-transport measurements reveal a sheet carrier density on the order of $\approx5-7\times10^{13}$ cm$^{-2}$, comparable to values typically achieved in pulsed laser deposition-grown SrTiO$_3$-based heterostructures, along with effective electrostatic tunability. This work demonstrates a simple, cost-effective, and industry-compatible route for engineering oxide 2DEGs, providing a versatile platform for scalable device fabrication and interfacial transport studies.

cond-mat.mtrl-sci↗

arXiv2025

Intrinsic Berry Curvature Driven Anomalous Hall and Nernst Effect in Co$_2$MnSn

Magnetic topological semimetals often exhibit unusual electronic and thermal transport due to nontrivial bulk band crossings, enabling simultaneous realization of large anomalous Hall and Nernst conductivities ($\sigma_{xy}$ and $\alpha_{xy}$). Here, a comprehensive experimental and theoretical study of the anomalous transport properties of ferromagnetic Co$_2$MnSn is reported. First-principles calculations reveal topological Weyl points producing significant Berry curvature, driving dominant intrinsic anomalous Hall/Nernst effects. Electronic and thermal transport measurements demonstrate robust anomalous transport with substantial conductivity values that persist at room temperature ($\sigma_{xy}\sim$ 500 S/cm, $\alpha_{xy}\sim$ 1.3 A/m/K). We also show how the chemical substitution (via tuning Fermi level) can boost these effects (up to $\sigma_{xy}\sim$ 1376 S/cm, $\alpha_{xy}\sim$ 1.49 A/m/K at 150 K). These findings position Co$_2$MnSn as a compelling platform for exploring topological transport phenomena and advancing next-generation thermoelectric and spintronic technologies.

cond-mat.mtrl-sci↗

arXiv2025

Magnetism and nonlinear charge transport in NiFe2O4/{\gamma}-Al2O3/SrTiO3 heterostructure: Toward Spintronic Applications

We present the synthesis and study of the magnetic and electronic properties of NiFe2O4/{\gamma}-Al2O3/SrTiO3 heterostructure. The {\gamma}-Al2O3/SrTiO3 interface hosts a high-mobility two-dimensional electron gas (2DEG) with large spin-orbit coupling, making it promising for spintronics applications if it can be coupled to a suitable source of spin currents. Here, we synthesize a ferrimagnetic insulating NiFe2O4(001) layer on {\gamma}-Al2O3(001)/SrTiO3(001) using a low-temperature reactive sputtering at 150 deg C without compromising the mobility and charge carrier density of the 2DEG at the {\gamma}-Al2O3(001)/SrTiO3(001) interface. The sheet resistance of both {\gamma}-Al2O3/SrTiO3 and NiFe2O4/{\gamma}-Al2O3/SrTiO3 exhibits metallic behavior down to cryogenic temperatures, with a low temperature upturn driven by the Kondo-like scattering. Most importantly, NiFe2O4/{\gamma}-Al2O3/SrTiO3 behaves as a magnetic diode at low temperatures, and its rectification performance increases significantly with increasing magnetic field strength giving rise to a robust magneto-electronic rectification effect at low temperatures, which provides a first step towards the development of all-oxide heterostructures capable of efficient spin-charge conversion.

cond-mat.mtrl-sci↗

arXiv2025

Leveraging high fluence and low pressure for pulsed laser deposition of high-mobility $\gamma$-Al$_2$O$_3$/SrTiO$_3$ heterostructure growth

High-mobility oxide heterostructures could be applied for high-frequency devices, transparent conductors, and spin-orbit logic devices. SrTiO$_3$ is one of the most studied oxide substrate materials for heterostructures. To date, the highest SrTiO3-based charge carrier mobility at 2 K was measured in the interfacial 2-dimensional electron gas (2DEG) of $\gamma$-Al$_2$O$_3$/SrTiO$_3$. The formation mechanism and origin of the high electron mobility are not yet fully understood. This investigation presents a successful growth protocol to synthesise high mobility $\gamma$-Al$_2$O$_3$/SrTiO$_3$ interfaces, and a description of the underlying growth optimisation. Furthermore, indicative features of high-mobility $\gamma$-Al$_2$O$_3$/SrTiO$_3$, including the room-temperature sheet resistance, are presented. Signs of epitaxial and crystalline growth are found in a high-mobility sample ($\mu^{10K} = 1.6 \times 10^4 \mathrm{cm}^2/\mathrm{Vs}$). Outlining the growth mechanisms and comparing 40 samples, indicates that high-fluence ($F > 3\mathrm{J}/\mathrm{cm}^2$) and low pressure ($P \approx 1 \times 10^{-6} \mathrm{mbar}$) are essential growth parameters for high-mobility $\gamma$-Al$_2$O$_3$/SrTiO$_3$ interfaces. $\gamma$-Al$_2$O$_3$ having single-element cations allows higher laser fluences during growth, compared to thin films with multi-element cations such as LaAlO$_3$, without causing stoichiometric imbalances.

cond-mat.mtrl-sci↗

arXiv2024

Superparamagnetic Superparticles for Magnetic Hyperthermia Therapy: Overcoming the Particle Size Limit

Iron oxide (e.g., Fe$_3$O$_4$ or Fe$_2$O$_3$) nanoparticles are promising candidates for a variety of biomedical applications ranging from magnetic hyperthermia therapy to drug delivery and bio-detection, due to their superparamagnetism, non-toxicity, and biodegradability. While particles of small size (below a critical size, ~20 nm) display superparamagnetic behavior at room temperature, these particles tend to penetrate highly sensitive areas of the body such as the Blood-Brain Barrier (BBB), leading to undesired effects. In addition, these particles possess a high probability of retention, which can lead to genotoxicity and biochemical toxicity. Increasing particle size is a means for addressing these problems but also suppresses the superparamagnetism. We have overcome this particle size limit by synthesizing unique polycrystalline iron oxide nanoparticles composed of multiple nanocrystals of 10 to 15 nm size while tuning particle size from 160 to 400 nm. These so-called superparticles preserve superparamagnetic characteristics and exhibit excellent hyperthermia responses. The specific absorption rates (SAR) exceed 250 W/g (HAC = 800 Oe, f = 310 kHz) at a low concentration of 0.5 mg/mL, indicating their capability in cancer treatment with minimum dose. Our study underscores the potential of size-tunable polycrystalline iron oxide superparticles with superparamagnetic properties for advanced biomedical applications and sensing technologies.

physics.app-ph↗

arXiv2024

The Discovery of Giant Positive Magnetoresistance in Proximity to Helimagnetic Order in Manganese Phosphide Nanostructured Films

The study of magnetoresistance (MR) phenomena has been pivotal in advancing magnetic sensors and spintronic devices. Helimagnets present an intriguing avenue for spintronics research. Theoretical predictions suggest that MR magnitude in the helimagnetic (HM) regime surpasses that in the ferromagnetic (FM) regime by over an order of magnitude. However, in metallic helimagnets like manganese phosphide, MR in the HM phase remains modest (10%), limiting its application in MR devices. Here, a groundbreaking approach is presented to achieve a giant low field MR effect in nanostructured manganese phosphide films by leveraging confinement and strain effects along with spin helicity. Unlike the modest MR observed in bulk manganese phosphide single crystals and large grain polycrystalline films, which exhibit a small negative MR in the FM region (2%) increasing to 8% in the HM region across 10-300 K, a grain size-dependent giant positive MR (90%) is discovered near FM to HM transition temperature (110 K), followed by a rapid decline to a negative MR below 55 K in manganese phosphide nanocrystalline films. These findings illuminate a novel strain-mediated spin helicity phenomenon in nanostructured helimagnets, presenting a promising pathway for the development of high-performance MR sensors and spintronic devices through the strategic utilization of confinement and strain effects.

physics.app-ph↗

arXiv2024

Tailoring magnetic and hyperthermia properties of biphase iron oxide nanocubes through post-annealing

Tailoring the magnetic properties of iron oxide nanosystems is essential to expand their biomedical applications. In this study, the 34 nm iron oxide nanocubes with two phases consisting of Fe3O4 and alpha-Fe2O3 were annealed for 2 hours in the presence of O2, N2, He, and Ar to tune the respective phase volume fractions and control the magnetic properties. X-ray diffraction and magnetic measurements were carried out post-treatment to evaluate the changes of the treated samples compared to the as-prepared, which showed an enhancement of the alpha-Fe2O3 phase in the samples annealed with O2, while the others indicated Fe3O4 enhancement. Furthermore, the latter samples indicated enhancements in the crystallinity and saturation magnetization while coercivity enhancement was most significant in the samples annealed with O2, resulting in the highest specific absorption rates (up to 1000 W/g) in all the applied fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia measurements. The general enhancement in the specific absorption rate post-annealing underscores the importance of the annealing atmosphere in the enhancement of the magnetic and structural properties of nanostructures.

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 $\cong 20.5$ $\mu$V/K/$\Omega$ 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 $\mu$V/K/$\Omega$). 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↗

arXiv2023

Temperature Evolution of Magnon Propagation Length in Tm$_3$Fe$_5$O$_{12}$ Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping

The magnon propagation length ($\langle\xi\rangle$) of a ferro/ferrimagnet (FM) is one of the key factors that controls the generation and propagation of thermally-driven spin current in FM/heavy metal (HM) bilayer based spincaloritronic devices. Theory predicts that for the FM layer, $\langle\xi\rangle$ is inversely proportional to the Gilbert damping ($\alpha$) and the square root of the effective magnetic anisotropy constant ($K_{\rm eff}$). However, direct experimental evidence of this relationship is lacking. To experimentally confirm this prediction, we employ a combination of longitudinal spin Seebeck effect (LSSE), transverse susceptibility, and ferromagnetic resonance experiments to investigate the temperature evolution of $\langle\xi\rangle$ and establish its correlation with the effective magnetic anisotropy field, $H_K^{\rm eff}$ ($\propto K_{\rm eff}$) and $\alpha$ in Tm$_3$Fe$_5$O$_{12}$ (TmIG)/Pt bilayers. We observe concurrent drops in the LSSE voltage and $\langle\xi\rangle$ below 200$^\circ$K in TmIG/Pt bilayers regardless of TmIG film thickness and substrate choice and attribute it to the noticeable increases in $H_K^{\rm eff}$ and $\alpha$ that occur within the same temperature range. From the TmIG thickness dependence of the LSSE voltage, we determined the temperature dependence of $\langle\xi\rangle$ and highlighted its correlation with the temperature-dependent $H_K^{\rm eff}$ and $\alpha$ in TmIG/Pt bilayers, which will be beneficial for the development of rare-earth iron garnet-based efficient spincaloritronic nanodevices.

cond-mat.mtrl-sci↗

arXiv2023

Competing Magnetic Interactions and Field-Induced Metamagnetic Transition in Highly Crystalline Phase-Tunable Iron Oxide Nanorods

The inherent existence of multi phases in iron oxide nanostructures highlights the significance of them being investigated deliberately to understand and possibly control the phases. Here, the effects of annealing at 250 0C with a variable duration on the bulk magnetic and structural properties of high aspect ratio bi-phase iron oxide nanorods with ferrimagnetic Fe3O4 and antiferromagnetic alpha-Fe2O3 is explored. Increasing annealing time under a free flow of oxygen enhanced the alpha-Fe2O3 volume fraction, and improved the crystallinity of the Fe3O4 phase, identified in changes in the magnetization as a function of annealing time. A critical annealing time of approximately 3 hours maximized the presence of both phases, as observed via an enhancement in the magnetization and an interfacial pinning effect. This is attributed to disordered spins separating the magnetically distinct phases which tend to align with the application of a magnetic field at high temperatures. The increased antiferromagnetic phase can be distinguished due to the field-induced metamagnetic transitions observed in structures annealed for more than 3 hours and was especially prominent in the 9-hour annealed sample. Our controlled study in determining the changes in volume fractions with annealing time will enable precise control over phase tunability in iron oxide nanorods, allowing custom-made phase volume fractions in different applications ranging from spintronics to biomedical applications.

physics.app-ph↗

arXiv2022

Spin Seebeck effect in iron oxide thin films: Effects of phase transition, phase coexistence, and surface magnetism

Understanding impacts of phase transition, phase coexistence, and surface magnetism on the longitudinal spin Seebeck effect (LSSE) in a magnetic system is essential to manipulate the spin to charge current conversion efficiency for spincaloritronic applications. We aim to elucidate these effects by performing a comprehensive study of the temperature dependence of LSSE in biphase iron oxide (BPIO = alpha-Fe2O3 + Fe3O4) thin films grown on Si (100) and Al2O3 (111) substrates. A combination of temperature-dependent anomalous Nernst effect (ANE) and electrical resistivity measurements show that the contribution of ANE from the BPIO layer is negligible compared to the intrinsic LSSE in the Si/BPIO/Pt heterostructure even at room temperature. Below the Verwey transition of the Fe3O4 phase, the total signal across BPIO/Pt is dominated by the LSSE. Noticeable changes in the intrinsic LSSE signal for both Si/BPIO/Pt and Al2O3/BPIO/Pt heterostructures around the Verwey transition of the Fe3O4 phase and the antiferromagnetic (AFM) Morin transition of the alpha-Fe2O3 phase are observed. The LSSE signal for Si/BPIO/Pt is found to be almost two times greater than that for Al2O3/BPIO/Pt, an opposite trend is observed for the saturation magnetization though. Magnetic force microscopy reveals the higher density of surface magnetic moments of the Si/BPIO film compared to the Al2O3/BPIO film, which underscores a dominant role of interfacial magnetism on the LSSE signal and thereby explains the larger LSSE for Si/BPIO/Pt.

cond-mat.mtrl-sci↗

arXiv2022

Exchange Bias and Interface-related Effects in Two-dimensional van der Waals Magnetic Heterostructures: Open Questions and Perspectives

The exchange bias (EB) effect is known as a fundamentally and technologically important magnetic property of a magnetic bilayer film. It is manifested as a horizontal shift in a magnetic hysteresis loop of a film subject to cooling in the presence of a magnetic field. The EB effect in van der Waals (vdW) heterostructures offers a novel approach for tuning the magnetic properties of the newly discovered single-layer magnets, as well as adds a new impetus to magnetic vdW heterostructures. Indeed, intriguing EB effects have recently been reported in a variety of low-dimensional vdW magnetic systems ranging from a weakly interlayer-coupled vdW magnet (e.g., Fe3GeTe2) to a bilayer composed of two different magnetic vdW materials (e.g., Fe3GeTe2/CrCl3, Fe3GeTe2/FePS3, Fe3GeTe2/MnPS3), to bilayers of two different vdW defective magnets (e.g., VSe2/MoS2), or to metallic ferromagnet/vdW defective magnet interfaces (e.g., Fe/MoS2). Despite their huge potential in spintronic device applications, the physical origins of the observed EB effects have remained elusive to researchers. We present here a critical review of the EB effect and associated phenomena such as magnetic proximity (MP) in various vdW heterostructure systems and propose approaches to addressing some of the emerging fundamental questions.

cond-mat.mtrl-sci↗

arXiv2021

Scaling of the thermally induced sign inversion of longitudinal spin Seebeck effect in a compensated ferrimagnet: Role of magnetic anisotropy

We report on a systematic investigation of the longitudinal spin Seebeck effect (LSSE) in a GGG(Gd3Ga5O12)/GdIG(Gd3Fe5O12)/Pt film series exhibiting an in-plane magnetic easy axis with a compensation temperature (T_Comp) that decreases from 270 to 220 K when decreasing GdIG film thickness from 272 to 31 nm, respectively. For all the films, the LSSE signal flips its sign below T_Comp. We demonstrate a universal scaling behavior of the temperature dependence of LSSE signal for our GdIG films around their respective T_Comp. Additionally, we demonstrate LSSE in a 31 nm GdIG film grown on a lattice-mismatched GSGG (Gd3Sc2Ga3O12) substrate that exhibits an out-of-plane magnetic easy axis at room temperature. However, this sample reveals a spin reorientation transition where the magnetic easy axis changes its orientation to in-plane at low temperatures. We observed a clear distinction in the LSSE signal for the GSGG/GdIG(31 nm)/Pt heterostructure, relative to GGG/GdIG(31nm)/Pt showing an in-plane magnetic easy axis. Our findings underscore a strong correlation between the LSSE signal and the orientation of magnetic easy axis in compensated ferrimagnets and opens the possibility to tune LSSE through effective anisotropy.

cond-mat.mtrl-sci↗

arXiv2018

Effects of external magnetic field and hydrostatic pressure on magnetic and structural phase transitions in Pr0.6Sr0.4MnO3

We investigate the effect of hydrostatic pressure on temperature dependence of magnetization and also the influence of magnetic field on linear thermal expansion in polycrystalline Pr0.6Sr0.4MnO3, which is ferromagnetic at room temperature (TC = 305 K) but its magnetization undergoes an abrupt decrease at TS = 89 K within the ferromagnetic state. Normal and inverse magnetocaloric effects around TC and TS, respectively, were reported earlier in this single phase compound [D. V. M. Repaka et al., J. Appl. Phys. 112, 123915 (2012)]. The thermal expansion shows an abrupt decrease at TS in zero magnetic field but it transforms into an abrupt increase at the same temperature under 7 T, which we interpret as the consequence of magnetic field-induced structural transition from a low-volume monoclinic (I2/a symmetry) to a high volume orthorhombic (Pnma symmetry) phase in corroboration with a published neutron diffraction study in zero magnetic field. While the external magnetic field does not change TS, application of a hydrostatic pressure of P = 1.16 GPa shifts the magnetic anomaly at TS towards high temperature. The pressure induced shift of the low-temperature anomaly (deltaTS = 27 K) is nine-times more than that of the ferromagnetic Curie temperature (deltaTC = 3K). Our results suggest that while hydrostatic pressure stabilizes the low temperature monoclinic phase at the expense of orthorhombic phase, magnetic field has an opposite effect.

cond-mat.mtrl-sci↗