Physics Research International

Semiclassical Modeling of Isotropic Non-Heisenberg Magnets for Spin and Linear Quadrupole Excitation Dynamics

Yousef Yousefi and Khikmat Kh. Muminov — Wed, 27 Mar 2013 17:13:23 +0000

Equations describing one-dimensional non-Heisenberg model are studied by use of generalized coherent states in real parameterization, and then dissipative spin wave equation for dipole and quadrupole branches is obtained if there is a small linear excitation from the ground state. Finally, it is shown that for such exchange-isotropy Hamiltonians, optical branch of spin wave is nondissipative.

Advances in Novel Optical Materials and Devices

Michael R. Gleeson, Yasuo Tomita, Sergi Gallego, and Robert McLeod — Thu, 14 Mar 2013 11:54:00 +0000

On the Divergenceless Property of the Magnetic Induction Field

Sergio Severini and Alessandro Settimi — Mon, 25 Feb 2013 07:46:44 +0000

Maxwell's equations beautifully describe the electromagnetic fields properties. In what follows we will be interested in giving a new perspective to divergence-free Maxwell’s equations regarding the magnetic induction field: . To this end we will consider some physical aspects of a system consisting of massive nonrelativistic charged particles, as sources of an electromagnetic field (e.m.) propagating in free space. In particular the link between conservation of total momentum and divergence-free condition for the magnetic induction field will be deeply investigated. This study presents a new context in which the necessary condition for the divergence-free property of the magnetic induction field in the whole space, known as solenoidality condition, directly comes from the conservation of total momentum for the system, that is, sources and field. This work, in general, leads to results that leave some open questions on the existence, or at least the observability, of magnetic monopoles, theoretically plausible only under suitable symmetry assumptions as we will show.

A Minireview of the Natures of Radiation-Induced Point Defects in Pure and Doped Silica Glasses and Their Visible/Near-IR Absorption Bands, with Emphasis on Self-Trapped Holes and How They Can Be Controlled

David L. Griscom — Wed, 13 Feb 2013 10:15:50 +0000

The natures of most radiation-induced point defects in amorphous silicon dioxide (a-SiO2) are well known on the basis of 56 years of electron spin resonance (ESR) and optical studies of pure and doped silica glass in bulk, thin-film, and fiber-optic forms. Many of the radiation-induced defects intrinsic to pure and B-, Al-, Ge-, and P-doped silicas are at least briefly described here and references are provided to allow the reader to learn still more about these, as well as some of those defects not mentioned. The metastable self-trapped holes (STHs), intrinsic to both doped and undoped silicas, are argued here to be responsible for most transient red/near-IR optical absorption bands induced in low-OH silica-based optical fibers by ionizing radiations at ambient temperatures. However, accelerated testing of a-SiO2-based optical devices slated for space applications must take into account the highly supralinear dependence on ionizing-dose-rate of the initial STH creation rate, which if not recognized would lead to false negatives. Fortunately, however, it is possible to permanently reduce the numbers of environmentally or operationally created STHs by long-term preirradiation at relatively low dose rates. Finally, emphasis is placed on the importance and utility of rigorously derived fractal-kinetic formalisms that facilitate reliable extrapolation of radiation-induced optical attenuations in silica-based photonics recorded as functions of dose rate backward into time domains unreachable in practical laboratory times and forward into dose-rate regimes for which there are no present-day laboratory sources.

A New Technology for Fast Two-Dimensional Detection of Proton Therapy Beams

Sun, 30 Dec 2012 12:45:40 +0000

The Micromesh Gaseous Structure, or Micromegas, is a technology developed for high count-rate applications in high-energy physics experiments. Tests using a Micromegas chamber and specially designed amplifiers and readout electronics adapted to the requirements of the proton therapy environment and providing both excellent time and high spatial resolution are presented here. The device was irradiated at the Roberts Proton Therapy Center at the University of Pennsylvania. The system was operated with ionization gains between 10 and 200 and in low and intermediate dose-rate beams, and the digitized signal is found to be reproducible to 0.8%. Spatial resolution is determined to be 1.1 mm (1σ) with a 1 ms time resolution. We resolve the range modulator wheel rotational frequency and the thicknesses of its segments and show that this information can be quickly measured owing to the high time resolution of the system. Systems of this type will be extremely useful in future treatment methods involving beams that change rapidly in time and spatial position. The Micromegas design resolves the high dose rate within a proton Bragg peak, and measurements agree with Geant4 simulations to within 5%.

Nonlinear Optics of Nanostructures

Vladimir I. Gavrilenko, Tatiana V. Murzina, and Goro Mizutani — Sun, 09 Dec 2012 14:27:16 +0000

Modeling of Optical Nanoantennas

Bedir B. Yousif and Ahmed S. Samra — Thu, 08 Nov 2012 09:40:16 +0000

The optical properties of plasmonic nanoantennas are investigated in detail using the finite integration technique (FIT). The validity of this technique is verified by comparison to the exact solution generalized Mie method (GMM). The influence of the geometrical parameters (antenna length, gap dimension, and shapes) on the antenna field enhancement and spectral response is discussed. Localized surface plasmon resonances of Au (gold) dimers nanospheres, bowtie, and aperture bowtie nanoantennas are modeled. The enhanced field is equivalent to a strong light spot which can lead to the resolution improvement of the microscopy and optical lithography, thus increasing the optical data storage capacity. Furthermore, the sensitivity of the antennas to index changes of the environment and substrate is investigated in detail for biosensing applications. We confirm that our approach yields an exact correspondence with GMM theory for Au dimers nanospheres at gap dimensions 5 nm and 10 nm but gives an approximation error of less than 1.37% for gap dimensions 1 nm and 2 nm with diameters approaching 80 nm. In addition, the far-field characteristics of the aperture bowtie nanoantenna such as directivity and gain are studied. The promising results of this study may have useful potential applications in near-field sample detection, optical microscopy, and so forth.

Quantitative Comparison of Five Different Photosensitizers for Use in a Photopolymer

Yue Qi, Michael R. Gleeson, Jinxin Guo, Sergi Gallego, and John T. Sheridan — Wed, 12 Sep 2012 11:18:07 +0000

Several studies of the time varying photon absorption effects, which occur during the photoinitiation process involving in photopolymer materials, have been presented. Three primary mechanisms have been identified: (i) the dye absorption, (ii) recovery, and (iii) bleaching. Based on an analysis of these mechanisms, the production of primary radicals can be physically described and modelled. In free radical photopolymerization systems, the excited dye molecules induce the production of the primary radicals, 𝑅•, which are key in determining how many monomers are polymerized. This, in turn, is closely related to the refractive index modulation formed during holographic recording. In this paper, to avoid the complexities involved in estimating the rate constant of intersystem crossing, 𝑘𝑠𝑡, in going from the excited singlet state dye to the excited triplet state dye, we introduce two rates, 𝑘𝑎𝑆 and 𝑘𝑎𝑇 these are the proposed rate constants of photon absorption in going from the ground state to the singlet and triplet states, respectively. Using the resulting model, four kinds of Xanthene dyes: Erythrosin B; Eosin Y; Phloxine B, Rose Bengal, and one Thiazine dye: Methylene Blue, are experimentally characterised for use in an AA/PVA photopolymer.

Coaxial Self-Trapping of White and Gray Regions of an Incandescent Field: A Bright Core with a Dark Cladding

Kailash Kasala and Kalaichelvi Saravanamuttu — Sun, 09 Sep 2012 16:06:36 +0000

We report the generation of a self-trapped incoherent hybrid beam comprising a dark-sheathed bright core. The hybrid beam originates from refractive index changes in a photocrosslinkable organosiloxane, which allow simultaneous and cooperative self-trapping of a gray ring with a white core embedded in a broad incandescent beam. The core narrowed and increased in intensity while the encircling gray ring decreased in intensity until rendered very dark. This dark sheath improves light confinement in the bright core and protects it from interactions with nearby self-trapped filaments. This is the first example of a self-trapped hybrid beam, which is moreover spatially and temporally incoherent.

Development of Laser-Produced Tin Plasma-Based EUV Light Source Technology for HVM EUV Lithography

Junichi Fujimoto, Tsukasa Hori, Tatsuya Yanagida, and Hakaru Mizoguchi — Wed, 05 Sep 2012 15:49:54 +0000

Since 2002, we have been developing a carbon dioxide (CO2) laser-produced tin (Sn) plasma (LPP) extreme ultraviolet (EUV) light source, which is the most promising solution because of the 13.5 nm wavelength high power (>200 W) light source for high volume manufacturing. EUV lithography is used for its high efficiency, power scalability, and spatial freedom around plasma. We believe that the LPP scheme is the most feasible candidate for the EUV light source for industrial use. We have several engineering data from our test tools, which include 93% Sn ionization rate, 98% Sn debris mitigation by a magnetic field, and 68% CO2 laser energy absorption rate. The way of dispersion of Sn by prepulse laser is key to improve conversion efficiency (CE). We focus on prepulsed laser pulsed duration. When we have optimized pulse duration from nanosecond to picosecond, we have obtained maximum 4.7% CE (CO2 laser to EUV; our previous data was 3.8%) at 2 mJ EUV pulse energy. Based on these data we are developing our first light source as our product: “GL200E.” The latest data and the overview of EUV light source for the industrial EUV lithography are reviewed in this paper.

Length Bidisperse Carbon Nanotubes Dispersions in Thermotropic Liquid Crystals

V. Popa-Nita and S. Buček — Wed, 29 Aug 2012 13:53:57 +0000

We study nematic liquid crystal driven alignment of carbon nanotubes dispersed in them. We extend the mesoscopic model presented in (P. Van der Schoot et al. 2008, V. Popa-Nita, and S. Kralj 2010) including the effect of length bidispersity of carbon nanotubes. The free energy of the mixture is written as the sum of the Doi free energy for lyotropic nematic ordering of the two carbon nanotubes types, the Landau-de Gennes free energy for the thermotropic ordering of liquid crystal, and the coupling term between liquid crystal molecules and carbon nanotubes. The phase ordering of the mixtures is analyzed as a function of volume fraction, the strength of coupling, and the temperature.

Design and Analysis of a THz Metamaterial Structure with High Refractive Index at Two Frequencies

Zan Lu, Bruno Camps-Raga, and N. E. Islam — Thu, 23 Aug 2012 17:42:17 +0000

The concept of a single frequency band, single high-refractive-index metamaterial has been extended and applied in the design of dual frequency band, dual high-refractive-index metamaterials in the THz regime. The structure design consists of twenty five unit cells with a surface area of 250 um by 250 um and a thickness of 5 um. Each cell has metallic structures embedded in a polyimide substrate. The return loss (S-parameter) analysis shows two strong electric responses at two frequency ranges, and the extracted constitutive parameters suggested high values of simultaneous dielectric constant and permeability at these frequencies. Results retrieved from the S-parameters also show high refractive index values. A first peak refractive index of 61.83 was observed at a resonant frequency of 0.384 THz, and another peak refractive index of 19.2 was observed at the resonant frequency 1.416 THz. Analysis show that higher refractive index at the second resonance frequency band is achievable through redesign of the structures, and modifications could lead to a single structure with multiple frequency, multiple high-refractive-index metamaterials that can be put to practical use.

Closed-Aperture Z-Scan Analysis for Nonlinear Media with Saturable Absorption and Simultaneous Third- and Fifth-Order Nonlinear Refraction

Xiangming Liu and Yasuo Tomita — Tue, 07 Aug 2012 09:06:21 +0000

We present a theory of open- and closed-aperture Gaussian beam Z-scan for nonlinear optical materials with saturable absorption and high-order nonlinear refraction. We show that an approximate expression for a transmitted intensity through the nonlinear optical material is possible by means of the Adomian’s decomposition method and the thin film approximation. The theory is applied to semiconductor CdSe quantum dot-polymer nanocomposite films. It is shown that the theory well explains measured results of open- and closed-aperture transmittances in the Z-scan setup. It is also shown that the nanocomposite film possesses simultaneous third- and fifth-order nonlinear refraction as well as saturable absorption of a homogeneously broadened type.

Zero Spatial Frequency Limit: Method to Characterize Photopolymers as Optical Recording Material

Thu, 19 Jul 2012 09:43:54 +0000

Photopolymers are useful for different holographic applications such as holographic data storage or diffractive optical elements. However, due to the presence of two different phenomena, polymer formation and monomer diffusion, it is difficult to characterize each parameter independently. We propose a direct method based on zero spatial frequency recording, to eliminate the diffusion influence, and on interferometric techniques, both in transmission and in reflection, to obtain quantitative values of shrinkage, polymerization rate, polymer refractive index and relation between intensity and polymerization, and so forth, This method has been implemented in the Holography and Optical Processing Group from the University of Alicante to characterize different photopolymers. In this paper, we present a compilation of the results obtained with this method for different photopolymers and we compare their characteristics.

Advanced Magnetic Materials

Arcady Zhukov, Mitsuteru Inoue, Manh-Huong Phan, and Vladimir Shavrov — Mon, 09 Jul 2012 14:59:32 +0000

A Review of the Optimisation of Photopolymer Materials for Holographic Data Storage

Jinxin Guo, Michael R. Gleeson, and John T. Sheridan — Mon, 25 Jun 2012 15:48:19 +0000

Photopolymers are very interesting as optically sensitive recording media due to the fact that they are inexpensive, self-processing materials with the ability to capture low-loss, high-fidelity volume recordings of 3D illuminating patterns. We have prepared this paper in part in order to enable the recognition of outstanding issues, which limit in particular the data storage capacity in holographic data storage media. In an attempt to further develop the data storage capacity and quality of the information stored, that is, the material sensitivity and resolution, a deeper understanding of such materials in order to improve them has become ever more crucial. In this paper a brief review of the optimisation of photopolymer materials for holographic data storage (HDS) applications is described. The key contributions of each work examined and many of the suggestions made for the improvement of the different photopolymer material discussed are presented.

Optical Second Harmonic Generation Microscopy as a Tool of Material Diagnosis

Hiroko Yokota, Junichi Kaneshiro, and Yoshiaki Uesu — Mon, 28 May 2012 18:01:16 +0000

The second harmonic generation microscope (SHGM) constructs images of intensity distributions of SH waves produced by the interaction of fundamental waves with a polar material. We have developed this nonlinear optical microscope in order to make possible nondestructive, three-dimensional (3D) observations of various kinds of inorganic and organic materials. The SHGM can disclose also inverted domain structures of antiparallel spontaneous polarizations using the interference with the reference SH waves. The observation principle and several applications to structural characterizations of LiNbO3 and LiTaO3 quasi-phase matching devices, domain structure analyses of a relaxor/ferroelectric solid solution Pb(Zn1/3Nb2/3)O3-9%PbTiO3 at the morphotropic phase boundary, development of order parameter in a quantum paraelectric relaxor Li-doped KTaO3, and antiphase polar domain structures of muscle fibers and myofibrils are surveyed by stressing the high effectiveness of the SHGM as a tool of material diagnosis.

Optical Second Harmonic Generation in Semiconductor Nanostructures

Thu, 17 May 2012 09:58:37 +0000

Optical second harmonic generation (SHG) studies of semiconductor nanostructures are reviewed. The second-order response data both predicted and observed on pure and oxidised silicon surfaces, planar Si(001)/SiO2 heterostructures, and the results related to the direct-current-and strain-induced effects in SHG from the silicon surfaces as well are discussed. Remarkable progress in understanding the unique capabilities of nonlinear optical second harmonic generation spectroscopy as an advanced tool for nanostructures diagnostics is demonstrated.

Microscopic Theory of Multipole Ordering in 𝑓-Electron Systems

Takashi Hotta — Sun, 13 May 2012 10:22:35 +0000

A microscopic framework to determine multipole ordering in 𝑓-electron systems is provided on the basis of the standard quantum field theory. For the construction of the framework, a seven-orbital Hubbard Hamiltonian with strong spin-orbit coupling is adopted as a prototype model. A type of multipole and ordering vector is determined from the divergence of multipole susceptibility, which is evaluated in a random phase approximation. As an example of the application of the present framework, a multipole phase diagram on a three-dimensional simple cubic lattice is discussed for the case of 𝑛=2, where n denotes the average 𝑓-electron number per site. Finally, future problems concerning multipole ordering and fluctuations are briefly discussed.

Magnetic and Magnetoelectric Properties of Rare Earth Molybdates

B. K. Ponomarev and A. Zhukov — Wed, 09 May 2012 13:07:04 +0000

We present results on ferroelectric, magnetic, magneto-optical properties and magnetoelectric effect of rare earth molybdates (gadolinium molybdate, GMO, and terbium molybdate, TMO, and samarium molybdate, SMO), belonging to a new type of ferroelectrics predicted by Levanyuk and Sannikov. While cooling the tetragonal β-phase becomes unstable with respect to two degenerate modes of lattice vibrations. The β-β′ transition is induced by this instability. The spontaneous polarization appears as a by-product of the lattice transformation. The electric order in TMO is of antiferroelectric type. Ferroelectric and ferroelastic GMO and TMO at room temperature are paramagnets. At low temperatures GMO and TMO are antiferromagnetic with the Neel temperatures 𝑇N=0.3 K (GMO) and 𝑇N=0.45 K (TMO). TMO shows the spontaneous destruction at 40 kOe magnetic field. Temperature and field dependences of the magnetization in TMO are well described by the magnetism theory of singlets at 4.2 K ≤ T ≤ 30 K. The magnetoelectric effect in SMO, GMO and TMO, the anisotropy of magnetoelectric effect in TMO at T = (1.8–4.2) K, the Zeeman effect in TMO, the inversion of the electric polarization induced by the laser beam are discussed. The correlation between the magnetic moment of rare earth ion and the magnetoelectric effect value is predicted. The giant fluctuations of the acoustic resonance peak intensity near the Curie point are observed.

Influence of Magnesium Substitution on Thermal and Electrical Properties of NiCuZn Ferrites for Microinductor Core Applications

M. Venkata Ramana, N. Ramamanohar Reddy, and K. V. Siva kumar — Tue, 08 May 2012 09:09:44 +0000

Two series of NiMgCuZn ferrites, that is, (1) NixMg0.6−xCu0.1Zn0.3Fe2O4 and sample G: Ni0.3Mg0.3−yCu0.1Zn0.5−yFe2O4 with 𝑥=0.0, 0.1, 0.2, 0.3 and (2) NixMg0.6−xCu0.1Zn0.3Fe2O4 with 𝑦=0.0, 0.1, 0.2 were synthesized and prepared by conventional ceramic double-sintering process and to use them as core materials for microinductor applications. The formation of single phase was confirmed by X-ray diffraction. The temperature and compositional variation of DC, AC electrical conductivities (σ) and thermoelectric power (𝛼) were studied on these two series of polycrystalline ferrospinels. The studies were carried out in wide range of temperature from 30 to 350°C. On the basis of thermoelectric study, the ferrites under present work were found to be shown as n-type and p-type transition. The electrical conduction in these ferrospinels is explained in the light of polaron hopping mechanism. These ferrite compositions have been developed for their use as core materials for microinductor applications.

Generalized Analytical Solutions for Nonlinear Positive-Negative Index Couplers

Zh. Kudyshev, G. Venugopal, and N. M. Litchinitser — Tue, 08 May 2012 08:20:28 +0000

We find and analyze a generalized analytical solution for nonlinear wave propagation in waveguide couplers with opposite signs of the linear refractive index, nonzero phase mismatch between the channels, and arbitrary nonlinear coefficients.

Second-Order Nonlinear Optical Microscopy of a H–Si(111)1 × 1 Surface in Ultra-High Vacuum Conditions

Yoshihiro Miyauchi — Wed, 11 Apr 2012 18:34:04 +0000

This paper reviews the use of optical sum frequency generation (SFG) and second harmonic generation (SHG) microscopy under ultra-high vacuum (UHV) conditions to observe the dynamics of a hydrogen terminated Si(111)1 × 1 surface. First, we took SFG and SHG microscopic images of the surface after IR light pulse irradiation and found that the SHG and nonresonant SFG signals were enhanced, probably due to the formation of dangling bonds after hydrogen desorption. Second, we observed time-resolved SFG intensity images of a H–Si(111)1 × 1 surface. After visible pump light irradiation, the nonresonant SFG signal increased at probe delay time 0 ps and then decreased over a life time of 565 ps. The resonant SFG signal reduced dramatically at 0 ps and then recovered with an anisotropic line shape over a life time of 305 ps. The areas of modulated SFG signals at delay time 277 ps were expanded with an anisotropic aspect. Finally, we observed SFG intensity images of hydrogen deficiency on a Si(111)1 × 1 surface as a function of temperature. These images of the H–Si(111) surface, taken with a spatial resolution of 5 μm at several temperatures from 572 to 744 K, showed that the hydrogen desorbs homogeneously.

Nuclear Wavepacket Dynamics of Alkali Adsorbates on Metal Surfaces Studied by Time-Resolved Second Harmonic Generation

Kazuya Watanabe and Yoshiyasu Matsumoto — Wed, 11 Apr 2012 14:10:44 +0000

This paper reviews recent efforts to understand the dynamics of coherent surface vibrations of alkali atoms adsorbed on metal surfaces. Time-resolved second harmonic generation is used for the coherent excitation and detection of the nuclear wavepacket dynamics of the surface modes. The principles of the measurement and the experimental details are described. The main focus is on coverage and excitation photon energy dependences of the coherent phonon dynamics for Na-, K-, and Cs-covered Cu(111). The excitation mechanism of the coherent phonon has been revealed by the ultrafast time-domain technique and theoretical modelings.

Improvement of Thermal Stability of Nd-Tb-Fe-Co-B Sintered Magnets by Additions of Pr, Ho, Al, and Cu

A. A. Lukin, E. I. Il'yashenko, A. T. Skjeltorp, and G. Helgesen — Mon, 09 Apr 2012 13:45:53 +0000

The present work investigates the influence of Pr, Al, Cu, B and Ho which were introduced into the Co-containing sintered magnets of Nd-Dy-Tb-Fe-Co-B type on the magnetic parameters (𝛼, 𝑖𝐻𝑐, 𝐵𝑟, 𝐵𝐻max). The effect of heat treatment parameters on magnetic properties was also studied. It was revealed that the essential alloying of NdFeB magnets by such elements as Dy, Tb, Ho, Co as well as by boron-forming elements, for example, by titanium, may lead to reducing of F-phase quantity, and, as a consequence, to decreasing of magnetic parameters. It was also shown that additional doping of such alloys by Pr, B, Al and Cu leads to a significant increase of the quantity of F-phase in magnets as well as solubility of the Dy, Tb, Ho and Co in it. This promotes the increase of magnetic parameters. It was possible to attain the following properties for the magnets (Nd0,15Pr0,35Tb0,25Ho0,25)15(Fe0,71Co0,29)bal · Al0,9Cu0,1B8,5 (at. %) after optimal thermal treatment {1175 K (3,6–7,2 ks) with slow (12–16 ks) cooling to 675 K and subsequently remaining at 𝑇=775 K for 3,6 ks—hardening}: 𝐵𝑟=0,88 T, 𝑖𝐻𝑐=1760 kA/m, 𝐵𝐻max=144 kJ/m3, 𝛼<|0,01|%/K in the temperature interval 223–323 K.

Control of Cross-Sections and Optical Nonlinearity of Pt Nanowires and the Roughness Effect

Y. Ogata and G. Mizutani — Mon, 09 Apr 2012 11:27:32 +0000

In this paper we review our fabrication of Pt nanowire arrays on MgO(110) faceted templates by a shadow deposition method and our control of their cross-sectional shapes by adjusting the deposition directions of platinum. We obtained nanowire arrays with 𝐶𝑠 and 𝐶2𝑣 macroscopic symmetries. These macroscopic symmetries influence optical second harmonic generation (SHG) susceptibility elements of the nanowire arrays sensitively. On the other hand, the roughness of the nanowires had an effect on the rotational SHG patterns as a function of the sample rotation angle around the surface normal. We tried to explain the pattern change by a second-order perturbation scheme with respect to the roughness amplitude.

Fundamental Problems of the Electrodynamics of Heterogeneous Media

N. N. Grinchik and Yu. N. Grinchik — Sun, 08 Apr 2012 08:02:22 +0000

The consistent physic-mathematical model of propagation of an electromagnetic wave in a heterogeneous medium is constructed using the generalized wave equation and the Dirichlet theorem. Twelve conditions at the interfaces of adjacent media are obtained and justified without using a surface charge and surface current in explicit form. The conditions are fulfilled automatically in each section of counting schemes for calculations. A consistent physicomathematical model of interaction of nonstationaly electric and thermal fields in a layered medium with allowance or mass transfer is constructed. The model is based on the methods of thermodynamics and on the equations of an electromagnetic field and is formulated without explicit separation of the charge carriers and the charge of an electric double layer.

Magneto-Optical and Magnetic Studies of Co-Rich Glass-Covered Microwires

Alexander Chizhik and Valentina Zhukova — Sun, 01 Apr 2012 14:49:04 +0000

The magnetization reversal process in the surface and volume areas of Co-rich glass-covered microwires has been investigated. The study has been performed in the wide series of microwires with chemical composition, geometry (thickness of glass coating) with the purpose of the tailoring of the giant magnetoimpedance effect. The comparative analysis of the magnetoelectric, magnetic, and magneto-optical experiments permits to optimise the giant magnetoimpedance ratio and elucidate the main properties of the magnetization reversal process in the different parts of the Co-rich microwire.

Sintering of Soft Magnetic Material under Microwave Magnetic Field

Thu, 29 Mar 2012 10:06:36 +0000

We have developed a simple process for sintering of soft magnetization materials using microwave sintering. The saturated magnetization (Ms) of sintered magnetite was 85.6 emu/g, which was as high as 95% of magnetite before heating (90.4 emu/g). On the other hand, the averaged remanence (Mr) and coercivity (Hc) of the magnetite after heating were 0.17 emu/g and 1.12 Oe under measuring limit of SQUID, respectively. For the sintering process of soft magnetic materials, magnetic fields of microwave have been performed in nitrogen atmosphere. Therefore, a microwave single-mode system operating at a frequency of 2.45 GHz and with a maximum power level of 1.5 kW was used. We can sinter the good soft magnetic material in microwave magnetic field. The sample shrank to 82% theoretical density (TD) from 45%TD of green body. The sintered sample was observed the microstructure by TEM and the crystal size was estimated the approximate average size is 10 nm.

Metamagnetic Phase Transitions in (𝐒𝐦𝟎.𝟓𝐆𝐝𝟎.𝟓)𝟎.𝟓𝟓𝐒𝐫𝟎.𝟒𝟓𝐌𝐧𝐎𝟑 Ceramics

Fedor N. Bukhanko — Sun, 25 Mar 2012 19:07:13 +0000

The temperature dependences of ac magnetic susceptibility of the (Sm0.5Gd0.5)0.55Sr0.45MnO3 ceramics provide evidence of the formation of a mixed insulating state with a specific quantum-disordered phase, in which the domains with a long-range antiferromagnetic order dominate at temperatures below 𝑇N≅48,5 K. Irreversible metamagnetic phase transition in the ferromagnetically ordered state is carried out at the critical field 𝐻c1∼25 kOe which remains constant in the temperature range from 4.2 K to 60 K. From the analysis of the magnetization isotherms, the conclusion can be made about a spontaneous phase transition into the state with charge and orbital ordering at temperatures below the critical value 𝑇CO∼60 K. It is supposed that short-range charge correlations exist in unusually large interval of temperatures ~90 K at temperatures above 𝑇CO that considerably exceeds the area of existence of local orbital correlations ~50 K.