T. K. Nath

Bio: T. K. Nath is an academic researcher from Indian Institute of Technology Kharagpur. The author has contributed to research in topics: Magnetization & Ferromagnetism. The author has an hindex of 31, co-authored 206 publications receiving 4262 citations. Previous affiliations of T. K. Nath include Duke University & Indian Institutes of Technology.

Ferromagnetism in Fe-doped ZnO nanocrystals: Experiment and theory

Abstract: Debjani Karmakar,1 S. K. Mandal,2 R. M. Kadam,3 P. L. Paulose,4 A. K. Rajarajan,5 T. K. Nath,2 A. K. Das,2 I. Dasgupta,6 and G. P. Das7 1Technical Physics & Prototype Engineering Division, Bhabha Atomic Research Center, Mumbai 400085, India 2Department of Physics & Meteorology, Indian Institute of Technology, Kharagpur 721302, India 3Radiochemistry Division, Bhabha Atomic Research Center, Mumbai 400085, India 4Tata Institute of Fundamental Research, Mumbai 400005, India 5Solid State Physics Division, Bhabha Atomic Research Center, Mumbai 400085, India 6Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India 7Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata 700032, India Received 18 August 2006; revised manuscript received 7 December 2006; published 2 April 2007

Strain-dependent magnetic phase diagram of epitaxial La0.67Sr0.33MnO3 thin films

Abstract: Effects of lattice strain on magnetic behavior of epitaxial La0.67Sr0.33MnO3 thin films grown by 90° off-axis sputtering have been studied. The size of epitaxial strain was varied using four different substrates, i.e., (001) LaAlO3, (001) SrTiO3, (001) La0.3Sr0.7Al0.65Ta0.35O9, and (110) NdGaO3. The observed magnetism of coherent epitaxial films grown on these substrates, particularly anisotropy and Curie temperature, exhibit strong correlations with lattice strains. Spin reorientation transitions have been observed. The dependence of Curie temperature on the bulk and Jahn–Teller strains has been determined.

Three-dimensional strain states and crystallographic domain structures of epitaxial colossal magnetoresistive la0.8ca0.2mno3 thin films

Abstract: The evolution of three-dimensional strain states and crystallographic domain structures of epitaxial colossal magnetoresistive La0.8Ca0.2MnO3 films have been studied as a function of film thickness and lattice mismatch with two types of (001) substrates, SrTiO3 and LaAlO3. In-plane and out-of-plane lattice parameters and strain states of the films were measured directly using normal and grazing incidence x-ray diffraction techniques. The unit cell volume of the films is not conserved, and it exhibits a substrate-dependent variation with film thickness. Films grown on SrTiO3 substrates with thickness up to ∼250 A are strained coherently with a pure (001)T orientation normal to the surface. In contrast, films as thin as 100 A grown on LaAlO3 show partial relaxation with a (110)T texture. While thinner films have smoother surfaces and higher crystalline quality, strain relaxation in thicker films leads to mixed (001)T and (110)T textures, mosaic spread, and surface roughening. The magnetic and electrical tra...

Strain modification of epitaxial perovskite oxide thin films using structural transitions of ferroelectric BaTiO3 substrate

Abstract: Effects of induced biaxial strain on the electrical transport and magnetic properties of epitaxial thin films of SrRuO3 and La0.67Sr0.33MnO3 by structural transitions of ferroelectric BaTiO3 substrates have been studied. Large jumps of electrical resistivity (∼5% in SrRuO3 and ∼12% in La0.67Sr0.33MnO3) and low field magnetization (∼70% in La0.67Sr0.33MnO3) have been observed in the films at the structural transition temperatures of BaTiO3 substrate. The hysteretic jumps are reproducible through many thermal cycles, and they can be attributed to strain effects induced by the substrate. The use of phase transitions of ferroelectric substrates to manipulate lattice strain of epitaxial thin film heterostructures can be a useful way to modify the properties of perovskite oxides.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Multiferroic and magnetoelectric materials

Abstract: A ferroelectric crystal exhibits a stable and switchable electrical polarization that is manifested in the form of cooperative atomic displacements. A ferromagnetic crystal exhibits a stable and switchable magnetization that arises through the quantum mechanical phenomenon of exchange. There are very few 'multiferroic' materials that exhibit both of these properties, but the 'magnetoelectric' coupling of magnetic and electrical properties is a more general and widespread phenomenon. Although work in this area can be traced back to pioneering research in the 1950s and 1960s, there has been a recent resurgence of interest driven by long-term technological aspirations.

Inorganic caesium lead iodide perovskite solar cells

Abstract: The vast majority of perovskite solar cell research has focused on organic–inorganic lead trihalide perovskites. Herein, we present working inorganic CsPbI3 perovskite solar cells for the first time. CsPbI3 normally resides in a yellow non-perovskite phase at room temperature, but by careful processing control and development of a low-temperature phase transition route we have stabilised the material in the black perovskite phase at room temperature. As such, we have fabricated solar cell devices in a variety of architectures, with current–voltage curve measured efficiency up to 2.9% for a planar heterojunction architecture, and stabilised power conversion efficiency of 1.7%. The well-functioning planar junction devices demonstrate long-range electron and hole transport in this material. Importantly, this work identifies that the organic cation is not essential, but simply a convenience for forming lead triiodide perovskites with good photovoltaic properties. We additionally observe significant rate-dependent current–voltage hysteresis in CsPbI3 devices, despite the absence of the organic polar molecule previously thought to be a candidate for inducing hysteresis via ferroelectric polarisation. Due to its space group, CsPbI3 cannot be a ferroelectric material, and thus we can conclude that ferroelectricity is not required to explain current–voltage hysteresis in perovskite solar cells. Our report of working inorganic perovskite solar cells paves the way for further developments likely to lead to much more thermally stable perovskite solar cells and other optoelectronic devices.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Abstract: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.