@article { ISI:000265933700042, title = {Origin of high room temperature ferromagnetic moment of nanocrystalline multiferroic BiFeO3}, journal = {Applied Physics Letters}, volume = {94}, number = {18}, year = {2009}, month = {MAY}, pages = {182507}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

Single phase nanocrystalline BiFeO3 of average crystallite size similar to 25 nm with very high magnetization at room temperature is synthesized by an autocombustion method. Magnetic measurements above room temperature show deviation between field cooled and zero field cooled magnetization below 645 K, the Neel temperature (T-N) of the bulk material, indicating intrinsic nature of ferromagnetism. However, observation of a broad magnetic transition above T-N of BiFeO3 and extended up to 800 K suggests the presence of Fe3O4 as a possible magnetic impurity phase. Evidence for the presence of Fe3O4 is obtained from detailed analysis of the powder x-ray diffraction pattern.

}, keywords = {bismuth compounds, Combustion synthesis, crystallites, ferromagnetic materials, high-temperature effects, magnetic impurities, Magnetic moments, Magnetisation, Multiferroics, Nanostructured materials, Neel temperature, X-ray diffraction}, issn = {0003-6951}, doi = {10.1063/1.3132586}, author = {Vijayanand, S. and Potdar, H. S. and Joy, Pattayil Alias} } @article { ISI:000273689600061, title = {Magnetic and dielectric properties and Raman spectroscopy of GdCrO3 nanoparticles}, journal = {Journal of Applied Physics}, volume = {107}, number = {1}, year = {2010}, month = {JAN}, pages = {013912}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

The rare earth orthochromites are extremely interesting due to the richness of their optical, dielectric, and magnetic properties as well as due to their multiferroic properties which make them suitable materials to study in the nanoregime. However, the wet-chemical synthesis of these materials in nanosize is nontrivial. Here, we report for the first time, the detailed Raman spectra as well as magnetic and dielectric properties of chemically synthesized GdCrO3 nanoparticles of size ranging from 40 to 60 nm. The magnetic properties are dictated by competing Cr3+-Cr3+, Gd3+-Cr3+, and Gd3+-Gd3+ superexchange interactions in different temperature regions, resulting into an antiferromagnetic ordering at 167 K due to the Cr3+-Cr3+ followed by weak ferromagnetic ordering due to the onset of Cr3+-Gd3+ interactions. At lower temperature, it shows weak antiferromagnetic ordering due to Gd3+-Gd3+ interaction. Below 95 K, GdCrO3 nanoparticles showed the presence of negative magnetization due to Gd3+ and Cr3+ interactions resulting into weak ferromagnetic coupling. The Raman spectroscopy shows the characteristic Raman shifts indicating that below 450 cm(-1), Gd3+ ions play a dominant role in determining the phonon frequencies of GdCrO3, and above 450 cm(-1), the Cr+3 ions dominate. We also present for the first time the low temperature dielectric constant and loss tangent data for GdCrO3 in a broad temperature and frequency range. The dielectric constant shows a decrease in comparison to the bulk values due to the size dependent effects. It also shows a peak centered at around 320 K above which it shows a sharp decrease. The dielectric loss value in GdCrO3 nanoparticles is quite small and shows an interesting frequency dependent anomaly at lower temperature which might be due to the coupling between magnetic and dielectric order parameters.

}, keywords = {dielectric losses, gadolinium compounds, Magnetisation, Multiferroics, nanofabrication, Nanoparticles, permittivity, phonons, Raman spectra, superexchange interactions}, issn = {0021-8979}, doi = {10.1063/1.3275926}, author = {Jaiswal, Adhish and Das, Raja and Vivekanand, K. and Maity, Tuhin and Abraham, Priya Mary and Adyanthaya, Suguna D. and Poddar, Pankaj} } @article { ISI:000293826800006, title = {Structural, magnetic and mossbauer spectral studies of nanocrystalline Ni0.5Zn0.5Fe2O4 ferrite powders}, journal = {Journal of Alloys and Compounds}, volume = {509}, number = {37}, year = {2011}, month = {SEP}, pages = {8999-9004}, publisher = {ELSEVIER SCIENCE SA}, address = {PO BOX 564, 1001 LAUSANNE, SWITZERLAND}, abstract = {

Nanocrystalline Ni0.5Zn0.5Fe2O4 powders, synthesized by a combustion method are investigated by X-ray diffraction, vibrating sample magnetometry and Mossbauer spectroscopic techniques. We adopt a strategy to systematically control the particle sizes between 4 and 45 nm simply by changing the elemental stoichiometric coefficient, Phi(e), of the combustion mixture. Curie temperature of the superparamagnetic particles of size 4 nm is higher than that of the bulk particles. Interestingly, bigger particles (45 nm) show a comparable room temperature saturation magnetization and exceptionally very high Curie temperature of 833 K, when compared to that of the bulk Ni0.5Zn0.5Fe2O4 material (563 K). (C) 2011 Elsevier B. V. All rights reserved.

}, keywords = {Chemical synthesis, Magnetisation, Mossbauer spectroscopy, Nanostructured materials}, issn = {0925-8388}, doi = {10.1016/j.jallcom.2011.06.047}, author = {Verma, Seema and Joy, Pattayil Alias and Kurian, Sajith} }