V. R. K. Murthy

Abstract: Chemistry of ferrites theoretical models of electrical properties of ferrites electrical conductivity and thermoelectric power of ferrites low frequency dielectric properties of ferrites transport mechanism in mixed ferrites at microwave frequencies magnetic properties at microwave frequencies theory and design of non-reciprocal microwave ferrite devices - isolators and circulators-ferrite phase shifters ferrite films and film devices.

Abstract: Composites of polyvinylidene fluoride (PVDF) with micron and nano sized BaTiO3 powders were developed for electromagnetic interference (EMI) shielding applications in the X band. PVDF-nano BaTiO3 composites show better shielding property compared to PVDF-micron sized BaTiO3 composites. The composite of PVDF with 40 vol% of nano BaTiO3 showed the best EMI shielding effectiveness and is about 9 dB. The contributions from reflection and absorption to the total EMI shielding effectiveness is same for the PVDF-BaTiO3 composites. Addition of small amount of silver particles improved the shielding properties of these composites due to the increased conductivity. An EMI shielding effectiveness of about 26 dB is obtained in the measured frequency range for the PVDF-20 vol% nano BaTiO3-10 vol% Ag composite of thickness 1.2 mm. Novel three phase composite combining the advantages of metal, nano ceramic and polymer is obtained with the potential for effective EMI shielding applications.

Abstract: The effects of substituting different cations (Mn, Zn, Mg and Co) at the A-site of AZrNb2O8 compounds on structural parameters such as packing fraction and B-site octahedral distortion were studied using X-ray powder diffraction in conjunction with Rietveld refinement. Variations in the dielectric constant (er) were explained by the ionic polarizability of the compositions. The quality factor (Q × f) and temperature coefficient of resonant frequency (τf) were correlated with the packing fraction and B-site octahedral distortions (δ) in these compositions, respectively.

Abstract: The electrical conductivity of some nickel-zinc ferrites is studied as a function of temperature. The ferrites with iron in excess show n-type conduction and those with iron in deficiency show p-type conduction. Seebeck coefficient, X-ray analysis, and saturation magnetisation are also carried out to discuss the conductivity of these ferrites. Es wird die elektrische Leitfahigkeit einiger Nickel-Zinkferrite als Funktion der Temperatur gemessen. Ferrite mit Eisenuberschus zeigen n-Leitfahigkeit, solche mit Eisenmangel p-Leitfahigkeit. Untersuchungen des Seebeckkoeffizienten, der Sattigungsmagnetisierung sowie Rontgenanlysis werden durchgefuhrt, um die Leitfahigkeit dieser Ferrite zu diskutieren.

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 …

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Abstract: 3d-transition-metal-doped ZnO films (n-type Zn1−xMxO (x=005–025): M=Co, Mn, Cr, Ni) are formed on sapphire substrates using a pulsed-laser deposition technique, and their magnetic and electric properties are examined The Co-doped ZnO films showed the maximum solubility limit Some of the Co-doped ZnO films exhibit ferromagnetic behaviors with the Curie temperature higher than room temperature The magnetic properties of Co-doped ZnO films depend on the concentration of Co ions and carriers

Abstract: Recent advances in the theory and experimental realization of ferromagnetic semiconductors give hope that a new generation of microelectronic devices based on the spin degree of freedom of the electron can be developed. This review focuses primarily on promising candidate materials (such as GaN, GaP and ZnO) in which there is already a technology base and a fairly good understanding of the basic electrical and optical properties. The introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature. There are a number of other potential dopant ions that could be employed (such as Fe, Ni, Co, Cr) as suggested by theory [see, for example, Sato and Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000)]. Growth of these ferromagnetic materials by thin film techniques, such as molecular beam epitaxy or pulsed laser deposition, provides excellent control of the dopant concentration and the ability to grow single-phase layers. T...