@article { ISI:000231564300102, title = {Effect of disorder on the magnetic properties of LaMn0.5Fe0.5O3}, journal = {Physical Review B}, volume = {72}, number = {5}, year = {2005}, month = {AUG}, pages = {054426}, publisher = {AMERICAN PHYSICAL SOC}, type = {Article}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

Polycrystalline LaMn0.5Fe0.5O3 is synthesized by a low-temperature method and the magnetic properties of the resulting powder have been studied after annealing the sample in air at different temperatures in the range 200 degrees C-1350 degrees C. Room temperature Mossbauer spectroscopic studies show that the Fe ions are present in the +3 oxidation state in the material. However, the magnetic properties vary widely in an unexpected manner when samples are annealed at different temperatures. Zero field cooled magnetization studies show a cusp below 100 K, for the sample annealed at 200 degrees C, indicating a spin-glass-like or superparamagnetic behavior. However, this cusp disappears completely when the sample is annealed at 700 degrees C but still showing a magnetic hysteresis loop with reduced magnetization at low temperatures. The cusp again appears when the sample is annealed at higher temperatures with increasing low-temperature magnetization. EPR and IR spectroscopic studies indicate changes in the distribution of Mn3+ and Fe3+ ions in the lattice. The overall results can be explained in terms of random distribution of Mn3+ and Fe3+ ions in the lattice and formation of some magnetic clusters, with the degree of distribution of the ions varying for samples annealed at different temperatures.

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.72.054426}, author = {Bhame, Shekhar D. and Joly, V. L. Joseph and Joy, Pattayil Alias} } @article { ISI:000229664600004, title = {Electronic structure and ferromagnetism of polycrystalline Zn1-xCoxO (0 <= x <= 0.15)}, journal = {Solid State Communications}, volume = {134}, number = {10}, year = {2005}, month = {JUN}, pages = {665-669}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, type = {Article}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

The electronic structure of polycrystalline ferromagnetic Zn1-x,CoxO (0.05 \<= x \<= 0.15) and the oxidation state of Co in it, have been investigated. The Co-doped polycrystalline samples are synthesized by a combustion method and are ferromagnetic at room temperature. XPS and optical absorption studies show evidence for Co2+ ions in the tetrahedral symmetry, indicating, substitution of Co2+ in the ZnO lattice. However, powder XRD and electron diffraction data shock the presence of Co metal in the samples. This give evidence to the fact that some Co2+ ion are incorporated in the ZnO lattice which gives changes in the electronic structure whereas ferromagnetism comes from the Co metal impurities present in the samples. (c) 2005 Elsevier Ltd. All rights reserved.

}, keywords = {Magnetically ordered materials, Optical properties, Semiconductors}, issn = {0038-1098}, doi = {10.1016/j.ssc.2005.03.013}, author = {Deka, Sasanka and Joy, Pattayil Alias} } @article { ISI:000238329100003, title = {Effect of thermal annealing on Fe40Ni38B18Mo4 thin films: modified Herzer model for magnetic evolution}, journal = {Journal of Physics D-Applied Physics}, volume = {39}, number = {10}, year = {2006}, month = {MAY}, pages = {1993-2000}, publisher = {IOP PUBLISHING LTD}, type = {Article}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {

Magnetic properties of nano-crystalline soft magnetic alloys have usually been correlated to structural evolution with heat treatment. However, literature reports pertaining to the study of nano-crystalline thin films are less abundant. Thin films of Fe40Ni38B18Mo4 were deposited on glass substrates under a high vacuum of approximate to 10(-6) Torr by employing resistive heating. They were annealed at various temperatures ranging from 373 to 773K based on differential scanning calorimetric studies carried out on the ribbons. The magnetic characteristics were investigated using vibrating sample magnetometry. Morphological characterizations were carried out using atomic force microscopy (AFM), and magnetic force microscopy (MFM) imaging is used to study the domain characteristics. The variation of magnetic properties with thermal annealing is also investigated. From AFM and MFM images it can be inferred that the crystallization temperature of the as-prepared films are lower than their bulk counterparts. Also there is a progressive evolution of coercivity up to 573 K, which is an indication of the lowering of nano-crystallization temperature in thin films. The variation of coercivity with the structural evolution of the thin films with annealing is discussed and a plausible explanation is provided using the modified random anisotropy model.

}, issn = {0022-3727}, doi = {10.1088/0022-3727/39/10/002}, author = {Hysen, T. and Deepa, S. and Saravanan, S. and Ramanujan, R. V. and Avasthi, D. K. and Joy, Pattayil Alias and D Kulkarni, S. and Anantharaman, Maliemadom R.} } @article { ISI:000236770900036, title = {Enhanced magnetostrictive properties of Mn substituted cobalt ferrite Co1.2Fe1.8O4}, journal = {Journal of Applied Physics}, volume = {99}, number = {7}, year = {2006}, month = {APR}, pages = {Article No. 107901}, publisher = {AMER INST PHYSICS}, type = {Article}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

The effect of substitution of Fe and Co by Mn on the magnetostrictive properties of the cobalt ferrite Co1.2Fe1.8O4 has been studied and compared. The studies on Co1.2-xMnxFe1.8O4 and Co1.2Fe1.8-xMnxO4 (0 \<= x \<= 0.4) showed a marked dependence of magnetostriction on the substitution of both Fe and Co by Mn. Higher magnetostriction is obtained for the substitution of Co by Mn whereas the magnetostriction is reduced substantially on the substitution of Fe by Mn. Higher magnetostriction at low magnetic fields and enhancement of the strain ratio have been observed for the substitution of Co by Mn. (c) 2006 American Institute of Physics.

}, issn = {0021-8979}, doi = {10.1063/1.2183356}, author = {Bhame, Shekhar D. and Joy, Pattayil Alias} } @article { ISI:000241157000039, title = {Evidence for intergranular tunnelling in polyaniline passivated alpha-Fe nanoparticles}, journal = {Nanotechnology}, volume = {17}, number = {18}, year = {2006}, month = {SEP}, pages = {4765-4772}, publisher = {IOP PUBLISHING LTD}, type = {Article}, address = {DIRAC HOUSE, TEMPLE BACK, BRISTOL BS1 6BE, ENGLAND}, abstract = {

Nanoparticles are of immense importance both from the fundamental and application points of view. They exhibit quantum size effects which are manifested in their improved magnetic and electric properties. Mechanical attrition by high energy ball milling (HEBM) is a top down process for producing fine particles. However, fineness is associated with high surface area and hence is prone to oxidation which has a detrimental effect on the useful properties of these materials. Passivation of nanoparticles is known to inhibit surface oxidation. At the same time, coating polymer film on inorganic materials modifies the surface properties drastically. In this work a modified set-up consisting of an RF plasma polymerization technique is employed to coat a thin layer of a polymer film on Fe nanoparticles produced by HEBM. Ball-milled particles having different particle size ranges are coated with polyaniline. Their electrical properties are investigated by measuring the dc conductivity in the temperature range 10-300 K. The low temperature dc conductivity (I-V) exhibited nonlinearity. This nonlinearity observed is explained on the basis of the critical path model. There is clear-cut evidence for the occurrence of intergranular tunnelling. The results are presented here in this paper.

}, issn = {0957-4484}, doi = {10.1088/0957-4484/17/18/039}, author = {Sunny, Vijutha and Narayanan, T. N. and Sajeev, U. S. and Joy, Pattayil Alias and Kumar, D. Sakthi and Yoshida, Yasuhiko and Anantharaman, Maliemadom R.} } @article { ISI:000239426700005, title = {Experimental comparison of the structural, magnetic, electronic, and optical properties of ferromagnetic and paramagnetic polycrystalline Zn1-xCoxO (x=0,0.05,0.1)}, journal = {Physical Review B}, volume = {74}, number = {3}, year = {2006}, month = {JUL}, pages = {Article No. 033201}, publisher = {AMERICAN PHYSICAL SOC}, type = {Article}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

Ferromagnetism at room temperature is observed in one case whereas paramagnetism down to 12 K is observed in the second case when polycrystalline Zn1-xCoxO is synthesized under almost identical conditions. Identical x-ray diffraction, optical absorption, and x-ray photoelectron spectroscopy results indicate the incorporation of Co2+ ions in the ZnO lattice in both cases. However, electron diffraction studies show the presence of Co metal impurities in the ferromagnetic samples, indicating that pure Co doped ZnO is not likely to be ferromagnetic.

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.74.033201}, author = {Deka, Sasanka and Pasricha, Renu and Joy, Pattayil Alias} } @article { ISI:000246431600023, title = {Enhanced permeability and dielectric constant of NiZn ferrite synthesized in nanocrystalline form by a combustion method}, journal = {Journal of the American Ceramic Society}, volume = {90}, number = {5}, year = {2007}, month = {MAY}, pages = {1494-1499}, publisher = {WILEY-BLACKWELL}, type = {Article}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

The performance parameters of Ni0.5Zn0.5Fe2O4, synthesized in the nanocrystalline form by an autocombustion method, have been investigated. The sample sintered at 1200 degrees C, with Bi2O3 as additive shows a very high value of initial permeability mu{\textquoteright}(i) of \> 400 at 1 MHz, with low loss. Similarly, a very high dielectric constant is obtained at lower frequencies. The results show that optimum magnetic and electrical properties can be achieved for the NiZn ferrite nanocrystalline powders synthesized by the present autocombustion method and sintered at a relatively lower temperature of 1200 degrees C when compared with a temperature of 1400 degrees C required for the materials synthesized by the conventional ceramic method.

}, issn = {0002-7820}, doi = {10.1111/j.1551-2916.2007.01560.x}, author = {Deka, Sasanka and Joy, Pattayil Alias} } @article { ISI:000243707500003, title = {Enhancement of the phase transformation temperature of gamma-Fe2O3 by Zn2+ doping}, journal = {Journal of Materials Chemistry}, volume = {17}, number = {5}, year = {2007}, month = {JAN}, pages = {453-456}, publisher = {ROYAL SOC CHEMISTRY}, type = {Article}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The phase transformation temperature of gamma-Fe2O3 to alpha-Fe2O3 is increased with Zn2+ doping and enhancement of the transition temperature by similar to 100 degrees C is obtained for doping of \>= 15 mol\% Zn in nanocrystalline gamma-Fe2O3 synthesized by an autocombustion method.

}, issn = {0959-9428}, doi = {10.1039/b616120k}, author = {Deka, Sasanka and Joy, Pattayil Alias} } @article { ISI:000256410700035, title = {Effect of sintering conditions and microstructure on the magnetostrictive properties of cobalt ferrite}, journal = {Journal of the American Ceramic Society}, volume = {91}, number = {6}, year = {2008}, month = {JUN}, pages = {1976-1980}, publisher = {BLACKWELL PUBLISHING}, type = {Article}, address = {9600 GARSINGTON RD, OXFORD OX4 2DQ, OXON, ENGLAND}, abstract = {

The effects of sintering temperature and dwell time on the magnetostrictive properties of polycrystalline cobalt ferrite synthesized by the conventional ceramic method have been investigated. The present study showed that the magnitude of magnetostriction strongly depends on the microstructure of the final sintered product. The presence of small and uniform grains with less porous structure in the sintered material leads to enhancement of the magnetostrictive strain. Higher magnetostriction is obtained for samples sintered at a relatively lower temperature of 1100 degrees C. These results are further corroborated by analyzing the effect of some additives during sintering on the microstructural and magnetostrictive properties.

}, issn = {0002-7820}, doi = {10.1111/j.1551-2916.2008.02367.x}, author = {Bhame, Shekhar D. and Joy, Pattayil Alias} } @article { ISI:000254416300010, title = {Enhanced shape anisotropy and magneto-optical birefringence by high energy ball milling in NixFe1-xFe2O4 ferrofluids}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {320}, number = {6}, year = {2008}, month = {MAR}, pages = {815-820}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Ferrofluids belonging to the series NixFe1-xFe2O4 were synthesised by two different procedures-one by standard co-precipitation techniques, the other by co-precipitation for synthesis of particles and dispersion aided by high-energy ball milling with a view to understand the effect of strain and size anisotropy on the magneto-optical properties of ferrofluids. The birefringence measurements were carried out using a standard ellipsometer. The birefringence signal obtained for chemically synthesised samples was satisfactorily fitted to the standard second Langevin function. The ball-milled ferrofluids showed a deviation and their birefringence was enhanced by an order. This large enhancement in the birefringence value cannot be attributed to the increase in grain size of the samples, considering that the grain sizes of sample synthesised by both modes are comparable; instead, it can be attributed to the lattice strain-induced shape anisotropy(oblation) arising from the high-energy ball-milling process. Thus magnetic-optical (MO) signals can be tuned by ball-milling process, which can find potential applications. (C) 2007 Elsevier B.V. All rights reserved.

}, keywords = {birefringence, Co-precipitation, ferrofluid, HEBM}, issn = {0304-8853}, doi = {10.1016/j.jmmm.2007.08.032}, author = {Nair, Swapna S. and Xavier, Francis and Joy, Pattayil Alias and Kulkarni, S. D. and Anantharaman, Maliemadom R.} } @article { ISI:000269206600022, title = {Effect of nickel nanofillers on the dielectric and magnetic properties of composites based on rubber in the X-band}, journal = {Applied Physics A-Materials Science \& Processing}, volume = {97}, number = {1}, year = {2009}, month = {OCT}, pages = {157-165}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Nickel-rubber nanocomposites were synthesized by incorporating ferromagnetic nickel nanoparticles in a natural rubber as well as neoprene rubber matrix. Complex dielectric permittivity and magnetic permeability of these composites were evaluated in the X-band microwave frequencies at room temperature using cavity perturbation technique. The dielectric loss in natural rubber is smaller compared to neoprene rubber. A steady increase in the dielectric permittivity is observed with increase in the content of nickel in both the composites. The magnetic permeability exhibits a steady decrease with increase in frequency and magnetic loss shows a relaxation at 8 GHz. The suitability of these composites as microwave absorbers is modeled based on the reflection loss which is dependant on the real and imaginary components of the complex dielectric permittivity and magnetic permeability.

}, issn = {0947-8396}, doi = {10.1007/s00339-009-5284-1}, author = {Jamal, E. Muhammad Abdul and Mohanan, P. and Joy, Pattayil Alias and Kurian, Philip and Anantharaman, Maliemadom R.} } @article { ISI:000274459600009, title = {Evidence for the co-existence of distorted tetrahedral and trigonal bipyramidal aluminium sites in SrAl12O19 from Al-27 NMR studies}, journal = {Solid State Communications}, volume = {150}, number = {5-6}, year = {2010}, month = {JAN}, pages = {262-266}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

Strontium aluminate, SrAl12O19, is a ceramic material having the hexagonal magnetoplumbite-type structure, with multiple Al coordination environments. An earlier low-field Al-27 solid-state NMR study reported five different Al sites in this system: one AlO4, one AlO5, and three AlO6 sites; whereas a later high-field study showed that the AlO5 site is a distorted AlO4 site with a very large quadrupolar coupling constant (similar to 20 MHz). Our magic angle spinning (MAS) and 3-quantum magic angle spinning (3QMAS) NMR studies at 7.05 T unambiguously show evidence for an AlO5 site. However, evidence for the presence of a distorted AlO4 site is obtained from studies at high fields (16.4 and 17.6 T), in addition to the AlO5 site. Thus the present solid-state NMR studies give evidence for the simultaneous presence of both the five-coordinated and distorted four-coordinated sites in this system. (C) 2009 Elsevier Ltd. All rights reserved.

}, keywords = {Local structure, MQMAS, Nuclear magnetic resonance, Strontium aluminate}, issn = {0038-1098}, doi = {10.1016/j.ssc.2009.11.008}, author = {Harindranath, K. and Viswanath, K. Anusree and Chandran, C. Vinod and Braeuniger, Thomas and Madhu, Perunthiruthy K. and Ajithkumar, Thalasseril G. and Joy, Pattayil Alias} } @article { ISI:000300591700013, title = {Effect of inter-particle interactions on the magnetic properties of magnetite nanoparticles after coating with dextran}, journal = {International Journal of Nanotechnology}, volume = {8}, number = {10-12, SI}, year = {2011}, month = {JAN}, pages = {907-915}, publisher = {INDERSCIENCE ENTERPRISES LTD}, address = {WORLD TRADE CENTER BLDG, 29 ROUTE DE PRE-BOIS, CASE POSTALE 896, CH-1215 GENEVA, SWITZERLAND}, abstract = {

Nanoparticles of magnetite (Fe3O4) are synthesised by a coprecipitation method and coated with the biocompatible polymer, dextran. The uncoated and dextran coated magnetite nanoparticles are characterised by powder X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and magnetic measurements. The magnetic properties of the uncoated and coated magnetite nanoparticles are compared to study the effect of inter-particle magnetic interactions on the magnetic characteristics. Absence of magnetic hysteresis at room temperature indicates the superparamagnetic nature of the two samples. Evidence for the effect of reduced inter-particle magnetic interactions is directly obtained from the field dependence of magnetisation at room temperature. The decreased superparamagnetic blocking temperature and the nature and shape of the field cooled magnetisation curve of the dextran coated sample further confirmed that the inter-particle magnetic interactions are completely suppressed after coating.

}, keywords = {dextran coating, magnetic interactions, magnetic properties, magnetite, Nanoparticles}, issn = {1475-7435}, author = {Sreeja, V. and Joy, Pattayil Alias} } @article { ISI:000307039700023, title = {Enhanced magnetic parameters in the morphotropic phase boundary region of nanocrystalline multiferroic Bi1-xLaxFeO3}, journal = {Solid State Communications}, volume = {152}, number = {16}, year = {2012}, month = {AUG}, pages = {1609-1612}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

Antiferromagnetic multiferroic BiFeO3 shows ferromagnetic characteristics by simultaneous substitution of Bi by La and decrease in the particle size to nanometer dimensions. Large changes in saturation and remnant magnetization, magnetic susceptibility at low and high fields, along with some anomalous changes in the magnetic transition temperature are observed in nanocrystalline Bi1-xLaxFeO3 system for 0.1 \<= x \<= 0.2. This compositional region corresponds to the morphotropic phase boundary (MPB) region separating the rhombohedral and orthorhombic phases, and the effect is similar to that observed in many ferroelectric systems. The present observation of enhanced ferromagnetic parameters in the MPB region of the nanocrystalline multiferroic La substituted BiFeO3 system, combined with the known ferroelectric characteristics, is suitable for future device applications. (C) 2012 Elsevier Ltd. All rights reserved.

}, keywords = {Bismuth ferrite, magnetic properties, Multiferroics, Nanocrystalline materials}, issn = {0038-1098}, doi = {10.1016/j.ssc.2012.05.011}, author = {Thakuria, P. and Joy, Pattayil Alias} } @article { ISI:000313149800004, title = {Enhancement in the magnetostriction of sintered cobalt ferrite by making self-composites from nanocrystalline and bulk powders}, journal = {ACS Applied Materials \& Interfaces}, volume = {4}, number = {12}, year = {2012}, month = {DEC}, pages = {6421-6425}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Sintered polycrystalline cobalt ferrite is a potential magnetostrictive smart material for applications as sensors and actuators. A novel concept of enhancing the magnetostrictive strain of sintered cobalt ferrite by making self-composites from nanosized and bulk powders with different particle sizes of the same material as components is reported. The self-composites give higher magnetostriction coefficient and strain derivative when compared to the sintered products obtained from the individual powders. The individual components give a maximum magnetostriction up to similar to 310 ppm, whereas up to similar to 370 ppm is obtained for a two-component system consisting of powders of two different sizes. On the other hand, a three-component self-composite made from starting powders of 3 nm, 40 nm and \>1 mu m give very high magnetostriction of similar to 400 ppm at 800 kA/m, suitable for making devices.

}, keywords = {Cobalt ferrite, Magnetostriction, Nanocrystalline, self-composite, Sintering}, issn = {1944-8244}, doi = {10.1021/am302053q}, author = {Mohaideen, Kamal Khaja and Joy, Pattayil Alias} } @article { ISI:000327467000003, title = {Evolution and magnetic characteristics of NiO-Ni(OH)(2) core-shell nanostructures}, journal = {Physical Chemistry Chemical Physics}, volume = {15}, number = {48}, year = {2013}, month = {OCT}, pages = {20808-20812}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The evolution and magnetic behaviour of NiO-Ni(OH)(2) core-shell nanostructures with different thicknesses of the hydroxide shell have been studied. The nickel hydroxide shell is found to alter the magnetic characteristics of nickel oxide at low temperatures and explains the origin of the exchange bias effect due to the anti-ferromagnetic NiO core and a ferromagnetic nickel hydroxide shell.

}, issn = {1463-9076}, doi = {10.1039/c3cp53612b}, author = {Mahajan, Mangesh B. and Joy, Pattayil Alias} } @article { ISI:000374350600073, title = {Enhancing the strain sensitivity of CoFe2O4 at low magnetic fields without affecting the magnetostriction coefficient by substitution of small amounts of Mg for Fe}, journal = {Physical Chemistry Chemical Physics}, volume = {18}, number = {15}, year = {2016}, month = {APR}, pages = {10516-10527}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Attaining high magnetostrictive strain sensitivity (d lambda/dH) with high magnetostriction strain (lambda) is desirable for sintered polycrystalline cobalt ferrite for various applications. It is shown that substitution of a small amount of Fe3+ by Mg2+ in CoMgxFe2-xO4 (x \< 0.1) gives a comparable maximum magnetostriction coefficient to that of the unsubstituted counterpart, with large improvement in the strain sensitivity at relatively low magnetic fields. A large increase in the magnetostriction coefficient is obtained at low magnetic fields for the substituted compositions. The magnetostriction parameters are further enhanced by magnetic field annealing of the sintered products. The results are analyzed based on powder XRD, Raman spectroscopy, XPS and magnetic measurements and based on the results from these studies, the changes in the magnetostriction parameters are correlated with the changes in the cation distribution, magnetic anisotropy and microstructure.

}, issn = {1463-9076}, doi = {10.1039/c6cp00369a}, author = {Anantharamaiah, P. N. and Joy, Pattayil Alias} }