Sayani Majumdar

Tampere University | UTA · Faculty of Information Technology and Communication Studies

Materials engineering on the nanoscale by precise control of growth parameters can lead to many unusual and fascinating physical properties. The development of pulsed laser deposition (PLD) 25 years ago has enabled atomistic control of thin films and interfaces and as such it has contributed significantly to advances in fundamental material science...

The colossal magnetoresistive insulator to metal switching of almost nine orders of magnitude under the significantly reduced magnetic field is achieved by illumination for the low bandwidth manganite thin films. Similarly, by changing the measuring bias voltage through the sample the required magnetic field for insulator-metal transition can be fu...

Universal, giant and nonvolatile resistive switching is demonstrated for oxide tunnel junctions with ferroelectric PbZr0.2Ti0.8O3, ferroelectric BaTiO3, and paraelectric SrTiO3 tunnel barriers. The effects are caused by reversible migration of oxygen vacancies between the tunnel barrier and bottom La2/3Sr1/3MnO3 electrode. The switching process, wh...

Energy efficiency, parallel information processing, and unsupervised learning make the human brain a model computing system for unstructured data handling. Different types of oxide memristors can emulate synaptic functions in artificial neuromorphic circuits. However, their cycle‐to‐cycle variability or strict epitaxy requirements remain a challeng...

Online training of deep neural networks (DNN) can be significantly accelerated by performing in situ vector‐matrix multiplication in a crossbar array of analog memories. However, training accuracies often suffer due to nonideal properties of synapses such as nonlinearity, asymmetry, limited bit precision, and dynamic weight update range within a co...

This work demonstrates a large area process for atomically thin 2D semiconductors to unlock the technological upscale required for their commercial uptake. The new atomic layer deposition (ALD) and conversion technique yields large area performance uniformity and tunability. Like graphene, 2D Transition Metal Dichalcogenides (TMDCs) are prone to up...

Online training of deep neural networks (DNN) can be significantly accelerated by performing in-situ vector matrix multiplication in a crossbar array of analog memories. However, training accuracies often suffer due to device non-idealities such as nonlinearity, asymmetry, limited bit precision and dynamic weight update range within constrained pow...

The current work reports an efficient deep neural network (DNN) accelerator where analog synaptic weight elements are controlled by ferroelectric domain dynamics. An integrated device-to-algorithm framework for benchmarking novel synaptic devices is used. In P(VDF-TrFE) based ferroelectric tunnel junctions, analog conductance states are measured us...

Quantum Conductance In article number 2201248, Gianluca Milano, Ilia Valov, and co‐workers review the state‐of‐the‐art of quantum conductance effects in memristive devices. Besides analyzing fundamental physicochemical phenomena and electronic ballistic transport in nanofilaments, recent developments in experimental observation of quantum effects i...

Quantum effects in novel functional materials and new device concepts represent a potential breakthrough for the development of new information processing technologies based on quantum phenomena. Among the emerging technologies, memristive elements which exhibit resistive switching that relies on the electrochemical formation/rupture of conductive...

The current work reports an efficient deep neural network (DNN) accelerator where synaptic weight elements are controlled by ferroelectric domain dynamics. An integrated device-to-algorithm framework for benchmarking novel synaptic devices is used. In P(VDF-TrFE) based ferroelectric tunnel junctions, analog conductance states are measured using a c...

This work demonstrates a large area process for atomically thin 2D semiconductors to unlock the technological upscale required for their commercial uptake. The new atomic layer deposition (ALD) and conversion technique yields large area performance uniformity and tunability. Like graphene, 2D Transition Metal Dichalcogenides (TMDCs) are prone to up...

We report the fabrication of the first Sr2FeMoO6 based organic spin valve device using Tris(8-hydroxyquinolinato) aluminium (Alq3) as a spin transport layer. The characterization of the device confirms hysteretic magnetoresistance with approximately 20%–30% switching between high and low resistance states at low temperatures. The results demonstrat...

Development of unconventional computing architectures, including neuromorphic computing, relies heavily on novel devices with properly engineered properties. This requires exploration of new functional materials and their designed interfaces. Ferroelectric memories including two-terminal ferroelectric tunnel junctions and three-terminal ferroelectr...

Among organic semiconductors, rubrene (RB; C42H28) is of rapidly growing interest for the development of organic and hybrid electronics due to exceptionally long spin diffusion length and carrier mobility up to 20 cm2V-1s-1 in single crystals. However, the fabrication of RB thin films resembling properties of the bulk remains challenging, mainly be...

Neuromorphic computing architectures demand the development of analog, non-volatile memory components operating at femto-Joule/bit operation energy. Electronic components working in this energy range require devices operating at ultrafast timescales. Among different non-volatile, analog memories, ferroelectric tunnel junctions (FTJs) have emerged a...

The integration and cooperation of mechanoreceptors, neurons and synapses in somatosensory systems enable humans to efficiently sense and process tactile information. Inspired by biological somatosensory systems, we report an optoelectronic spiking afferent nerve with neural coding, perceptual learning and memorizing capabilities to mimic tactile s...

The development of neuromorphic architectures depends on the engineering of new functional materials and material interfaces. Here, we present a study on organic ferroelectric tunnel junctions (FTJs) comprising a metal/ferroelectric/semiconductor stack with varying charge carrier density in the semiconducting electrode and demonstrate fast, volatil...

Activated by action potentials and Ca2+ ion migration, neurotransmitters in biological synapses are released from vesicles at the presynaptic membrane to the cleft and bonded to receptors on the postsynaptic membrane. The bonded neurotransmitters modify the electrochemical properties of the postsynaptic membrane and, thereby, the synaptic plasticit...

Ferroelectric tunnel junctions (FTJs) are a promising candidate for non-volatile memories and memristor-based computing circuits. Thus far, most research has focused on FTJs with a perovskite oxide ferroelectric tunnel barrier. As the need for high-temperature epitaxial film growth challenges the technological application of such inorganic junction...

The technology of spintronics, where, in addition to the electronic charge, electron spin also carries information, promises the future generation of electronics combining standard microelectronics with spin-dependent effects that arise from the interaction between spin of the carriers and the externally applied magnetic fields. Since the discovery...

A high absorption coefficient and a narrow absorption band in squaraine (SQ) dyes have resulted in rapidly growing interest in them as a donor material in photovoltaic devices. The exciton dissociation process in organic systems proceeds via a multistep mechanism where the electron-hole pairs (charge transfer states) involved in the current generat...

We report the effect of photonic field on the electronic and magnetic structure of a low bandwidth manganite PCMO thin film. In particular, the present study confirmed a mechanism that was recently proposed to explain how optical excitation can bias or directly activate the metamagnetic transition associated with the colossal magnetoresistance (CMR...

The field of organic spintronics gained momentum since the last decade where the motivation was mainly to explore the advantage of low spin orbit and hyperfine coupling strengths of organic semiconductors for achieving long spin diffusion length and time in the spintronic devices. Initial years saw both promising results and substantial challenges...

Functional oxides with a perovskite crystal lattice of type ABO 3 may possess corresponding oxygen‐deficient modulation structures, which can be used to tailor material properties including magnetism, ferroelectricity, and superconductivity. One prototypical example is the brownmillerite crystal structure of type ABO 2.5 [1‐5], which due to its hig...

To actualize the high spintronic application potential of complex magnetic oxides, it is essential to fabricate these materials as thin films with the best possible magnetic and electrical properties. Sr2FeMoO6 is an outstanding candidate for such applications, but presently no thin film synthesis route, which would preserve the magnetic properties...

The role of proximity contact with magnetic oxides is of particular interest from the expectations of the induced spin polarization and weak interactions at the graphene/magnetic oxide interfaces, which would allow us to achieve efficient spin-polarized injection in graphene-based spintronic devices. A combined approach of topmost-surface-sensitive...

We report photo-induced colossal magnetoresistive insulator-metal transition (IMT) in Pr0.6Ca0.4MnO3 thin films under much reduced applied magnetic field. The colossal effect was studied as a function of film thickness and thus with variable structural properties. Thorough structural, magnetic and magnetotransport characterization under light shows...

We have investigated the effect of grain boundary related defects on the electronic transport properties of the colossal magnetoresistive low bandwidth manganite Pr0.6Ca0.4MnO3 (PCMO) thin films. A series of PCMO films were prepared by pulsed laser deposition method on MgO and STO substrates. Characterizations of the structural, magnetic and magnet...

We report the growth of well-crystallized and epitaxially textured Pr0.6Ca0.4MnO3 thin films on SrTiO3 substrates by pulsed laser deposition at considerably low substrate temperatures, as low as 450 ◦C, without high-temperature post-annealing treatments. Although a strong ferromagnetic interaction as well as a large irreversible metamagnetic transi...

Pure, fully textured and c-axis oriented Sr2FeMoO6 films were deposited on SrTiO3 and (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates with different thicknesses. A decrease in substrate induced strain was observed in films on SrTiO3 with increasing thickness, but the strain in the films on (LaAlO3)0.3(Sr2AlTaO6)0.7 was nearly constant within the whole film th...

We report fabrication of hybrid organic semiconductor-inorganic complex oxide interface of rubrene and La0.67Sr0.33MnO3 (LSMO) for spintronic devices using pulsed laser deposition (PLD) and investigate the interface structure and chemical bonding-dependent magnetic properties. Our results demonstrate that with proper control of growth parameters, t...

A systematic study of epitaxially grown Sr2FeMoO6 thin films on SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrLaAlO4 and MgO single crystal substrates were made. Transmission electron microscopy investigations showed sharp substrate/films interfaces and increased defect concentration with increased lattice mismatch, indicating defect formation such as dislo...

Pulsed Laser Deposition (PLD) technique is applied to produce organic semiconductor (OS) rubrene thin film for spintronics applications. The use of organic material for spintronics is motivated by the advantages such as long spin diffusion length due to low spin-orbit and hyperfine coupling 1,2 , chemical tuning of electronic functionality, easy st...

Photo-induced magnetization has been studied in small-bandwidth manganite Pr1−x Cax MnO3 (x = 0.1) (PCMO) bulk and thin films. It is observed that the persistent change in magnetization under optical excitation is much stronger in epitaxial thin films of PCMO compared to the bulk. This change is manifested in a change of both coercive field and Cur...

The complex linear and nonlinear ac susceptibility have been thoroughly investigated in the low bandwidth manganite compound Pr1-xCaxMnO3 (PCMO) for the doping range x = 0.0-0.3 with and without a superimposed background dc field. The dynamical ac response shows substantial differences between the samples. The sample with x = 0.1 is found to have t...

The complex ac susceptibility is studied in the low bandwidth manganite Pr $_{1-x}$ Ca $_x$ MnO $_3$ at doping range $x = 0.3 - 0.5$ with and without a superimposed background dc field. It is found that all the samples had a frustrated magnetic phase. The fraction of the frustrated magnetic phase in the samples diminished as the Ca concent...

Structural phase transitions driven by oxygen vacancy ordering can drastically affect the properties of transition metal oxides. S. van Dijken, L. D. Yao, and co-workers demonstrate on page 2789 that the focused electron beam of a transmission electron microscope can be used to control structural phase transitions in epitaxial La2/3 Sr1/3 MnO3 . Th...

Structural phase transitions driven by oxygen-vacancy ordering can drastically affect the properties of transition metal oxides. The focused electron beam of a transmission electron microscope (TEM) can be used to control structural phase transitions in epitaxial La2/3Sr1/3MnO3. The ability to induce and characterize oxygen-deficient structural pha...

We report melting of the charge-ordered state in low bandwidth manganite PCMO (x = 0.3 - 0.5) thin films under substantially lower magnetic field. Two different in situ post-deposition annealing conditions were applied on the PCMO thin films grown by pulsed laser deposition at a deposition temperature of 500 �C, which is significantly lower compare...

Recent experimental reports suggest the formation of a highly spin-polarized interface ("spinterface") between a ferromagnetic Co electrode and a metal-phthalocyanine molecule. Another report shows an almost 60% giant magnetoresistance (GMR) response measured on Co/H 2 Pc-based single molecule spin valves. In this article, we compare the spin injec...

Epitaxial thin films of half-metallic oxide La0.7Sr0.3MnO3 (LSMO) have been grown in two crystalline orientations, one with the c-axis out-of-plane, the (001) orientation, and one with the c-axis in-plane, the (110) orientation. For the (110) oriented growth, there is no polar discontinuity at the substrate-film interface and hence no dead layer fo...

This article presents a comparison of spin transport mechanism in two �-conjugated organic polymers namely, regiorandom and regioregular poly (3-hexyl thiophenes) with same elemental composition but different regioregularity of the constituent atoms leading to different crystallinity and charge carrier mobility. Spin-valve devices made with both po...

This article presents a comparative study of persistent photo-induced magnetization in intermediate and low bandwidth perovskite manganite thin films, and analyzes the possible mechanisms for the observed differences in light of their structural and magnetic properties. Intermediate bandwidth manganite La0.9Ca0.1MnO3 (LCMO) and low bandwidth mangan...

Magnetotransport of La0.7Sr0.3MnO3 (LSMO)/regioregular poly3-hexylthiophene (rr-P3HT) interfaces were studied at 5–300 K to gain insight of spin transport in polymer coated LSMO. LSMO films on SrTiO3 (STO), MgO, and quartz substrates were characterized in pristine state, after depositing rr-P3HT and after removing rr-P3HT. Application and removal o...

High dielectric constant and its dependence on structural strain and grain boundaries (GB) in La0.7Sr0.3 MnO3 (LSMO) thin films are reported. X-ray diffraction, magnetization, and magneto-transport measurements of the LSMO films, made by pulsed laser deposition on two different substrates—MgO and SrTiO3 (STO), were compared to co-relate magnetic pr...

Persistent photo-induced magnetization (PPM) in low bandwidth manganite Pr1−xCaxMnO3 (PCMO) thin film is reported in the low hole doped regime (x = 0.1). X-ray diffraction, x-ray photoelectron spectroscopy, and magnetic measurements in dark and under illumination on the as-grown, vacuum, and oxygen annealed thin films of PCMO showed that the PPM ef...

We report on the effect of oxygen on the Jahn-Teller distortion and dynamic magnetic properties of low hole-doped Pr(0.9)Ca(0.1)MnO(3) thin films, using micro-Raman spectroscopy and the temperature dependent ac susceptibility, as a function of the frequency, dc field bias, and thermal cycles. The as-grown and vacuum annealed thin films show a high...

The influence of in situ oxygen annealings on narrow electronic bandwidth Pr0.9Ca0.1MnO3 films are investigated in the complex phase separation region. Measurements by x-ray diffractometry and SQUID magnetometry reveal that relatively high deposition temperature at 700 °C relaxes the lattice by twin boundaries while the lower deposition temperature a...

Magnetoresistive Sr2FeMoO6 thin films were grown by pulsed laser deposition with three different thicknesses 150 nm, 270 nm and 500 nm. Structural, magnetic and magneto-transport properties of the films were measured. Structural properties showed that impurity phases are formed when the film thickness exceed limiting thickness over 300 nm. Otherwise no...

High dielectric constant and its dependence on structural strain and grain boundaries (GB) in La 0.7 Sr 0.3 MnO 3 (LSMO) thin films are reported. X-ray diffraction, magnetization, and magneto-transport measurements of the LSMO films, made by pulsed laser deposition on two different substrates—MgO and SrTiO 3 (STO), were compared to co-relate magnet...

This article addresses the most challenging question facing the organic spintronics community today – what causes the universal loss of Giant Magnetoresistance (GMR) signal in organic spin valve devices made with different spin-polarized electrodes and organic semiconductor spacers? Careful analysis of our own and other experimental results availab...

Magnetoresistive double perovskite Sr(2)FeMoO(6) thin films were grown with two different deposition pressures on SrTiO(3), MgO and NdGaO(3) substrates by pulsed laser deposition and thorough structural, magnetic and magneto-transport characterization was made. According to x-ray diffraction, all the films were phase pure and fully textured. Indica...

Magnetic nanocrystalline MnO particles have been synthesized in a silica glass matrix by the sol–gel method at calcination temperatures up to 1000 °C. EPR spectra of 0.1 mol% MnO doped silica gel and glasses studied in the temperature range 10–290 K show with the exception of those samples calcined at 900 and 1000 °C 6-line characteristic Mn(II) hy...

The present paper reports detailed structural and magnetic characterization of the low-bandwidth manganite Pr(1-x)Ca(x)MnO(3) (with x = 0.0-0.5) (PCMO) polycrystalline samples. With increasing Ca content, reduction of the unit cell volume and improvement in perovskite structure symmetry was observed at room temperature. Magnetic characterization sh...

The effects of ex situ vacuum and oxygen annealing treatments on thin films of the low-bandwidth compound Pr(1-x)Ca(x)MnO(3) (PCMO) are investigated. Structural and magnetic measurements reveal that increased ferromagnetism can be achieved by oxygen annealing treatment, which is linked to the increased Mn(4+) ion content, as observed from x-ray pho...