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 …

I and i

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.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

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.

Ferromagnetic materials

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

Magnetic and electric properties of transition-metal-doped ZnO films

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...

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Wide band gap ferromagnetic semiconductors and oxides

Ni–Cu–Zn ferrite materials have been extensively used in multilayer chip inductors because of their remarkable properties at higher frequencies. In the present work, single phase Ni0.35Cu0.05Zn0.60Fe1.98O4-δ ferrite, has been prepared by microwave sintered (MS) method. In comparison with the conventional sintering method (CS), the sintering temperature and time for this MS method were significantly reduced to 30 min and 950°C from 5 h and 1250°C for the CS process. The frequency dependence of the dielectric properties such as dielectric constant (e'), dielectric loss (tan δ) were studied. The temperature dependence of magnetic initial permeability (μi) was studied. The saturation magnetization was also studied as a function of magnetic field. These microwave sintered ferrites results were compared with the properties of ferrites prepared by conventional sintering method in normal heating. Microwave sintering improves structural as well as electromagnetic parameters measured and thus makes the ferrite more suitable in microwave applications and electromagnetic devices.

STRUCTURAL, ELECTRICAL AND MAGNETIC CHARACTERIZATION OF Ni–Cu–Zn SPINEL FERRITES

Electro optic Kerr effect studies of polar-polar binary liquid mixtures

Internal friction Q -1 of Mn-Zn spinel ferrites in the manganese-rich region, developed for their use as TV deflection coil yokes, has been studied in the temperature range from 300 to 630 K. Two distinct stress induced relaxation peaks have been observed in the internal friction versus temperature curves. The magnetic transition has been observed to change with the concentration of zinc. The effect of magnetic field on the temperature dependence of internal friction has also been studied. The increase of zinc content in this system drastically alters the acoustic relaxations. The results are discussed in the light of Jahn-Teller distortion and cationic exchange between octahedral and tetrahedral sublattices and clustering of octahedral Mn 3+ ions.

Effect of Magnetic Field on the Temperature Variation of Internal Friction Loss of Mn-Zn Spinel Ferrites in the Manganese-Rich Region

We report the theoretical work on the photonic band gap structures suitable for microwave frequency region formed by magnetic materials ( e = 9.87 and μ = 2.17 ) using plane wave expansion method. The structures under analysis are two-dimensional square and triangular lattices. The calculated band gap between 10 and 20 GHz region is anlaysed for the effect due to lattice spacing and the property of the material. The results are also compared with that of pure dielectric case. Obtained results indicate that both impedance and effective refractive index are responsible for the gap width and mid-gap frequency.

V. R. K. Murthy

Papers

STRUCTURAL, ELECTRICAL AND MAGNETIC CHARACTERIZATION OF Ni–Cu–Zn SPINEL FERRITES

Electro optic Kerr effect studies of polar-polar binary liquid mixtures

Effect of Magnetic Field on the Temperature Variation of Internal Friction Loss of Mn-Zn Spinel Ferrites in the Manganese-Rich Region

Numerical study of the effect of permeability on square and triangular microwave band gap structures

Effect of crystal structure on microwave dielectric properties of Li2SrTa2(1−x)Nb2xO7 compounds