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Curie Temperature (curie + temperature)
Kinds of Curie Temperature Selected AbstractsMagnetization and Curie Temperature of Ilmenite,Hematite CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006Liliana Navarrete The morphology, structure, and magnetic properties of the magnetic semiconductor ceramic Ilmenite,Hematite (IH), (1,x)FeTiO3,xFe2O3, were studied as a function of the composition x. The magnetic ordering temperatures that we observed were consistently higher than those reported previously and were, for most of the composition range, above room temperature. We rule out the formation of Fe clusters as the origin of the magnetic properties. These magnetic properties of IH ceramics, in combination with their semiconducting characteristics, render them promising for spin-electronic applications. [source] A Macroporous Perovskite Manganite from Colloidal Templates with a Curie Temperature of 320 K.CHEMINFORM, Issue 34 2003Eun Ok Chi Abstract For Abstract see ChemInform Abstract in Full Text. [source] A new temperature-sensitive contrast mechanism for MRI: Curie temperature transition-based imagingCONTRAST MEDIA & MOLECULAR IMAGING, Issue 1 2007F. Settecase Abstract A temperature-sensitive MRI contrast mechanism is proposed based on the physical property, the Curie temperature (Tc), at which a ferromagnetic material transitions to paramagnetic state and vice versa. To evaluate the feasibility of this new contrast mechanism, experiments were performed with solid gadolinium metal, which has a Tc of 20°C. In phantom and ex vivo experiments, the magnetic susceptibility artifact area decreased with increasing temperature transitioning across Tc (p,<,0.05). Similar results would be expected for a variety of ferromagnetic substances with substance-specific Tc values. Temperature-sensitive MRI contrast agents harnessing this mechanism may be used to (1) indicate regional attainment of specific temperatures in thermotherapy, (2) render an accumulated contrast agent more or less visible by the external application of appropriate heating or cooling, or (3) quantify tissue temperature based on MR image characteristics and magnetic susceptibility artifact caused by a ferromagnetic,paramagnetic transitioning substance. Copyright © 2007 John Wiley & Sons, Ltd. [source] Unusual Lattice-Magnetism Connections in MnBi NanorodsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Kyongha Kang Abstract Lattice parameter, particle size, and thermal expansion results obtained from high-temperature synchrotron transmission X-ray diffraction are reported for magnetostructual NiAs-type MnBi nanorods embedded in a Bi matrix. The structural data are consistent with elevated-temperature magnetic measurements that indicate a first-order nanorod Curie transition at 520,K, significantly depressed from the bulk MnBi Curie temperature of 633,K. The data suggest that the unit cell volume dependence of the magnetic behavior,also known as the volume exchange striction,of the MnBi compound is the determining factor underlying this phenomenon. The results imply that materials with magnetostructural transitions of technological interest may be altered by strain effects to tailor the interatomic distances towards the critical transition values. [source] Photoresponsive Ferroelectric Liquid-Crystalline PolymersADVANCED FUNCTIONAL MATERIALS, Issue 1 2007P. Beyer Abstract The photoresponse of ferroelectric smectic side-chain liquid-crystalline (LC) polymers containing a photoisomerizable azobenzene derivative as a covalently linked photochromic side group is investigated. By static measurements in different photostationary states, the effect of trans,cis isomerization on the material's phase-transition temperatures and its ferroelectric properties (spontaneous electric polarization PS and director tilt angle ,) are analyzed. It turns out that the Curie temperature (transition SC* to SA) can be reversibly shifted by up to 17,°C. The molecular mechanism of this "photoferroelectric effect" is studied in detail using time-resolved measurements of the dye's optical absorbance, the director tilt angle, and the spontaneous polarization, which show a direct response of the ferroelectric parameters to the molecular isomerization. The kinetics of the thermal reisomerization of the azo dye in the LC matrix are evaluated. A comparison to the reisomerization reaction in isotropic solution (toluene) reveals a faster thermal relaxation of the dye in the LC phase. [source] Evaluation of ferromagnetic shape-memory alloys by the extended Hückel methodIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 3 2007Kei Ehara Student Member Abstract Ferromagnetic shape-memory alloy (SMA) are powerful candidates as actuators, pressure sensors, magnetic sensors, etc. Magnetic-field-induced strain has been observed in many ferromagnetic SMA. The magnetic-field-induced strain is a reversible transformation in the martensite phase with the magnetic field. We have investigated the property of the ferromagnetic shape-memory materials by the extended Hückel method, and estimated the ferromagnetic shape-memory of Fe,Pt and Fe,Pd alloys at high temperatures. We used two physical quantities, i.e. cohesive energy and energy fluctuation, to measure the stability of the materials. On the basis of the cohesive energy and energy fluctuation, we discuss the characteristics of ferromagnetic SMA, in which the energy fluctuation is a measure of thermal stability of the metals and/or alloys. The martensite structure is unstable, which means that the energy fluctuation has to be controlled to a small value to keep the martensite phase. Furthermore, it is estimated that the energy fluctuation is associated with the Curie temperature. The Curie temperature is an essential parameter for ferromagnetic materials. From the discussion presented above, we can propose the following: (i) Alloys possessing a low cohesive energy are associated with a high mobility of atoms and are suitable for ferromagnetic shape-memory materials; (ii) Alloys showing a low energy fluctuation show ferromagnetic shape-memory and are favored for use as memory devices. We found that I (iodine) is the best dopant for Fe,Pt ferromagnetic SMA, and Tc (technetium) is the best dopant for Fe,Pd ferromagnetic SMA. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Physical and Electrical Properties of Nanosized Mn- and Cr-Doped Strontium Y-Type Hexagonal FerritesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Muhammad Javed Iqbal Nanometer-sized crystallites of Y-type strontium hexaferrite, Sr2Ni2Fe12O22 and its Mn- and Cr-doped derivatives have been synthesized by the sol,gel method. Y-type phase formation was achieved at a considerably lower temperature of 950°C than is required in the traditional solid-state method (1200°C). The effect of doping of manganese at the tetrahedral site, Sr2Ni2,xMnx Fe12O22 (x=0.0,2.0), and chromium at octahedral site, Sr2Ni2 Fe12,yCryO22 (y=0.0,1.5), has been studied. The crystal structure remains unaffected by the substitutions. The crystallite size in the range of 13,45 nm is calculated from the X-ray diffraction data. The energy-dispersive X-ray fluorescence analysis shows that Y-type hexaferrites can be prepared with a base of strontium. The extent of doped Cr+3 ions at the octahedral site has been increased from the reported maximum value of y=1.5. Scanning electron micrographs of the samples showed a homogenous microstructure. The dc electrical resistivity studies show that these hexaferrites exhibit high resistivity at room temperature. Cr-doped samples have comparatively higher resistivity than Mn-doped samples. The doubly doped (Cr+Mn) samples possess high resistivity (7.37 × 109,-cm), a low dielectric constant (33.88 at 3000 Hz), and a high Curie temperature (>698 K). The dielectric energy losses are minimized by increasing the Mn and Cr contents of the synthesized samples. [source] Effect of BiScO3 and LiNbO3 on the Piezoelectric Properties of (Na0.5K0.5)NbO3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2009Xueyi Sun Lead-free potassium sodium niobate-based piezoelectric ceramics (1,y)(Na0.5,0.5xK0.5,0.5xLix)NbO3,yBiScO3 ( y=0.01, x=0,0.06) have been prepared by an ordinary sintering process. The XRD analysis showed that the structure changes from orthorhombic to tetragonal with the increase of x (at y=0.01, abbreviated as KNNBSL100x). At room temperature, the polymorphic phase transition from the orthorhombic to the tetragonal phase was identified at approximately 0.02,x,0.04. The piezoelectric and ferroelectric properties were significantly enhanced. The temperature dependences of the relative permittivity revealed that the Curie temperature was increased with the addition of LiNbO3. These solid solution ceramics are promising as potential lead-free candidate materials. [source] Addition of a Sr, K, Nb (SKN) Combination to PZT(53/47) for High Strain ApplicationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007Niall J. Donnelly A lead zirconate titanate composition incorporating the dopants Sr, K, and Nb (SKN) in the specific ratio 4:1:3 has been studied. In principle, the SKN should act as a donor dopant but since its addition reduced the grain size from 11.4 ,m (for 1% SKN) to 1.5 ,m (for 5% SKN), the overall effect was found to be more complicated. It was observed that the addition of SKN reduced the Curie temperature, by 16°C/mol (%) and broadened the dielectric peak. X-ray measurements further suggested that the ceramic was a mixture of rhombohedral and tetragonal phases and that the room temperature c/a ratio of the tetragonal phase decreased with SKN addition. The piezoelectric coefficient d33, determined from high field unipolar drives, gave an optimum value of 779 pm/V for the 0.02 SKN compositions, which also exhibited a relatively high Curie temperature of 356°C. Competing effects of enhanced domain wall mobility from donor doping and reduced mobility due to smaller grain size may explain the observed compositional variation in the measured material properties. Materials based on this composition are attractive for high performance piezoelectric actuator applications such as fuel injection. [source] Analysis of Phase Coexistence in Fe2O3 -Doped 0.2PZN,0.8PZT Ferroelectric Ceramics by Raman Scattering SpectraJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Man-Kang Zhu In this work, we suggested a method to evaluate quantitatively the effect of doping oxide on the phase coexistence of PbZr1,xTixO3 (PZT)-based ceramics through the analysis of the Raman scattering spectra. Theoretically, the degenerated T3u mode in the cubic phase of PZT will transform as A1(3) and E(4) modes in the tetragonal phase or as rhombohedral (R) modes in the rhombohedral phase below the Curie temperature, which set up the theoretical base to study the phase coexistence in ferroelectric materials. Through separation by fitting of the Raman bands, the shifts and intensities of different Raman vibration modes were determined. A calculation equation representing the phase coexistence was put forward based on the theoretical analysis of the degenerated T3u modes. The results showed that a turning point appears at the Fe2O3 addition of 0.3%. The variation in the electrical properties of the Fe2O3 -doped Pb(Zn1/3Nb2/3)O3 (PZN),PZT ceramics also affirmed the turning point of the phase evolution as the addition of Fe2O3. [source] Thermal Stability of (1,x)BiScO3,xPbTiO3 Piezoelectric Ceramics for High-Temperature Sensor ApplicationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Si Chen High-temperature piezoelectric (1,x)BiScO3,xPbTiO3 ceramics with composition (x=0.62, 0.63, 0.64, and 0.65) near the morphotropic phase boundary were fabricated. A thermal depoling experiment was used to investigate the stability of polarization at the temperature range from 200° to 460°C. The results indicated that samples with rhombohedral phase began to depole when the temperature was higher than 300°C, while samples with a tetragonal phase showed good resistance to thermal depoling up to 440°C, close to their Curie temperature. [source] Ferroelectric and Piezoelectric Properties of Na1,xBaxNb1,xTixO3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006J. T. Zeng Piezoelectric ceramics Na1,xBaxNb1,xTixO3 with low BaTiO3 concentrations x have been prepared by the solid-state reaction method, and their ferroelectric and piezoelectric properties have been studied. The ceramics are classic ferroelectrics when x,0.10, and the ferroelectric,paraelectric phase transition becomes diffusive when x,0.15. A low doping level of BaTiO3 changes the NaNbO3 ceramics from antiferroelectric to ferroelectric. With the increase in BaTiO3 doping level, the Curie temperature of ceramics decreases linearly and the remnant polarization and coercive field also decrease, while their dielectric constant increases. Na0.9Ba0.1Nb0.9Ti0.1O3 ceramics show the largest piezoelectric constant d33 (147 pC/N) and good sinterability, suggesting that it is a good candidate for lead-free piezoelectric ceramics. [source] Phase Transition and Failure at High Temperature of Bismuth-Layered Piezoelectric CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006Liaoying Zheng High-temperature bismuth-layered piezoelectric ceramics (CaxSr1,x)Bi4Ti4O15 have been prepared by the conventional solid reaction method. Our results reveal that there is a "phase transition induced by the composition" taking place in the solid solution at around x=0.4. During transition, the crystal structure changes from orthorhombic to pseudo-tetragonal and then back to orthorhombic. Although all (CaxSr1,x)Bi4Ti4O15 (with any x value) undergo a second-order ferroelectric-to-ferroelectric phase transition at about 200°C below their Curie temperature, only the ceramic with x=0.4 exhibits a failure in piezoelectric properties during the transition. It is suggested that, on the basis of the X-ray photoelectron spectroscopy results, this material failure is induced by the high concentration of oxygen vacancies in the material during the phase transition. [source] Chemical Synthesis of Nanocrystalline Strontium Bismuth Tantalate Powders Using Tantalum,Tartarate ComplexJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006Asit Baran Panda Nanocrystalline strontium bismuth tantalate (SrBi2Ta2O9; SBT) powders have been synthesized through complete dehydration of an aqueous solution mixture of tantalum tartarate, strontium salt of ethylenediaminetetraacetic acid, and bismuth,triethanolamine complex. Single-step calcination of the fluffy, mesoporous, carbonaceous dehydrated precursor mass at 700°C/2 h results in nanosized SBT powders, with average particle size ,15 nm. When palletized and sintered at 950°C/4 h these powders show a relative density of 97.6% of theoretical value, and a maximum dielectric constant value of 1387 at Tc (Curie temperature)=279°C, when measured at 100 kHz. [source] Revisit to the Origin of Grain Growth Anomaly in Yttria-Doped Barium TitanateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2001Jung-Kun Lee In this study, the effect of atmosphere during calcining and sintering of Y2O3 -doped BaTiO3 was investigated to reveal the origin of the anomaly of grain growth and conductivity as a function of Y2O3 content. Samples with various atmospheric histories were prepared. Microstructural and electrical variations were observed using SEM, dielectric (,r vs T) and thermopower measuring techniques, and impedance spectroscopy. An abrupt decrease in grain growth and a transition from semiconducting to insulating behavior were observed when the Y2O3 concentration exceeded 0.3 mol% and the samples were heat-treated in an O2 atmosphere. In contrast, the samples treated under N2+ 5% H2 atmosphere revealed neither grain growth anomaly nor conductivity anomaly even though the Y2O3 concentration was much greater than 3 mol%. The undoped BaTiO3 samples also demonstrated increased average grain size with increased oxygen partial pressure. Therefore, it was suggested that the grain growth anomaly did not result from the formation of cation vacancies V,Ba or V,,Ti. To investigate the origin of the grain growth anomaly, the Curie temperature, concentration of free electrons, and impedance spectra were measured. The grain growth anomaly and conductivity anomaly were associated with abrupt changes in all the measurements. These abrupt changes could be explained by the partial incorporation of donor dopants. Consequently, the origin of the anomaly in the microstructure and electrical properties are discussed in terms of grain-boundary segregation of the donor dopant. [source] Synthesis of Phase-Pure Pb(ZnxMg1,x)1/3Nb2/3O3 up to x= 0.7 from a Single Mixture via a Soft-Mechanochemical RouteJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Seiji Shinohara Phase-pure perovskite Pb(ZnxMg1,x)1/3Nb2/3O3 solid solution (PZxM1,xN) is obtained for x, 0.7 by heating a milled stoichiometric mixture of PbO, Mg(OH)2, Nb2O5, and 2ZnCO3·3Zn(OH)2·H2O at 1100°C for 1 h. Percent perovskite (fP) with respect to total crystalline phase decreases with increasing temperature of subsequent heating then increases to 900°C for the mixtures where x, 0.8 and milled for 3 h. For mixtures with x= 0.9 and x= 1, fP decreases monotonically. Curie temperature increases almost linearly with increasing x up to x= 0.7. The maximum dielectric constant at 1 kHz is 2×104 and 1.7×104 for the mixture with x= 0.4 and x= 0.7, respectively. The stabilization mechanism of strained perovskite is discussed. [source] Electrical Resistivity and Phase Transformation in SteelsMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 1 2003O. N. Mohanty Elektrischer Widerstand; Phasenumwandlung; Magnetische Eigenschaften Abstract Changes in electrical resistance accompanying transformations in steels with magnetic change (e.g. , , martensite/bainite) and without magnetic change (e.g. , , ,, above Curie temperature) have been examined; the former class affects the resistivity the latter does not. Next, while the efficacy of electrical resistivity measurement in capturing the well-known features of austenite stabilization (e.g. over , ageing, reversibility, and influence of prior martensite amount and so on) in high carbon steels has been reported in an earlier publication, new features (e.g. increase in resistance -increase at very low temperatures, change in temperature co-efficient of resistivity in the stabilized material etc.) are highlighted here. Finally, the work shows that a quantitative estimate of precipitation in the copper bearing, age-hardenable HSLA-100 steel during tempering can be done by continuous electrical resistivity measurement. These data also allow an in-depth kinetic analysis using the Johnson-Mehl-Avrami equation. Zusammenhang zwischen elektrischem Widerstand und Phasenumwandlungen in Stählen Änderungen des elektrischen Widerstands wurden im Zusammenhang mit Phasenumwandlungen, die zu Änderungen der magnetischen Eigenschaften führen (z.B. , , Martensit/Bainit), und solchen, die keine Änderungen der magnetischen Eigenschaften bewirken (z.B. , , , oberhalb der Curie-Temperatur), untersucht. Während sich die erste Umwandlungsart auswirkt, gilt dies für die andere nicht. Während über die Empfindlichkeit von Widerstandsmessungen zur Erfassung der Austenitstabilisierung (z.B. Überalterung, Umkehrbarkeit, Einfluß des vorher vorhandenen Martensitanteils, usw.) in übereutektoiden Stählen in einer früheren Veröffentlichung berichtet wurde, wird im zweiten Teil der hier vorgelegten Veröffentlichung auf neuerdings erfassbare Merkmale (z.B. der Anstieg des Widerstands bei sehr niedrigen Temperaturen, die Änderung der Temperaturabhängigkeit des Widerstands im stabilisierten Material, usw.) eingegangen. Schließlich zeigt die Arbeit, daß durch kontinuierliche Widerstandsmessungen während des Anlassens eine quantitative Abschätzung der Ausscheidungsgehalte im kupferhaltigen, ausscheidungsverfestigenden HSLA-100-Stahl erfolgen kann. Die Daten hierzu erlauben zudem eine vertiefte kinetische Analyse auf Basis der Johnson-Mehl-Avrami-Gleichung. [source] Piezoelectric and ferroelectric properties of [(K0.4725Na0.4725)Li0.055]NbO3,(Ag0.5Li0.5)TaO3 lead-free ceramicsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 5 2007Jiagang Wu Abstract New lead-free piezoelectric (1 , x)[(K0.4725Na0.4725)Li0.055]NbO3, x (Ag0.5Li0.5)TaO3 [(1 , x)KNNL,x ALT] ceramics were prepared by conventional sintering. Piezoelectric and ferroelectric properties and Curie temperature of the ceramics were studied. The (1 , x)KNNL,x ALT (x = 0.04) ceramics exhibit good properties (d33 , 252 pC/N, kp , 41%, TC , 471 °C, To,t = 47 °C, Pr = 33.1 ,C/cm2, Ec = 10.6 kV/cm). These results show that (1 , x)KNNL,x ALT (x = 0.04) ceramic is a promising lead-free piezoelectric material for high temperature application. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Microstructure and electrical properties of (1,x)(K0.5Na0.5)NbO3,x BiFeO3 piezoelectric ceramicsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008Xiang Li Abstract Lead,free ceramics (1,x)(K0.5Na0.5)NbO3,x BiFeO3 doped with 1 mol% Fe2O3 (KNNBF/x) have been synthesized by pressureless sintering. With the Fe2O3 doping, the KNNBF/x ceramics can be well sintered at 1085,1100 °C and exhibit a pure perovskite structure with x < 0.013. It was found that the crystal structure of the KNNBF/x ceramics changed from orthorhombic to tetragonal and then to pseudocubic phase with the increase of BiFeO3 content. The composition KNNBF/0.013 near the tetragonal symmetry that separates the orthorhombic and pseudocubic phases exhibits improved electrical properties: d33 = 173 pC/N, kp = 0.40, ,r = 905, tan , = 4%, Pr = 26 ,C/cm2, and Ec = 11.2 kV/cm, with a high Curie temperature (TC) of about 388 °C. Our results suggest that KNNBF/x are promising lead-free high temperature piezoelectric ceramics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of Nb substituted for Fe on the microstructure and magnetic properties of Fe-based nanocomposite alloyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007N. Q. Hoa Abstract The influence of Nb substituted for Fe on the microstructure and magnetic properties including the magnetoimpedance effect of a Fe-based have been investigated. The nanocomposite structure composed of ultra-fine Fe(Si) grains embedded in an amorphous matrix was obtained by annealing the Fe-based amorphous alloy prepared by rapidly-quenched method. The measurements of thermomagnetic curves indicated that the Curie temperature of the amorphous phase of the samples decreases with increasing Nb content. The optimal heat treatment was performed at Ta = 480 °C for 30 min and showed that the ultrasoft magnetic properties of nanocomposite materials were obtained. The magnetoimpedance (MI) of these samples has been studied in range frequency from 1MHz to 5 MHz and varying a dc magnetic field within 300 Oe. The correlation between the MI effect and the soft magnetic properties is discussed. The incremental permeability ratio (PR) showed the drastic changes of soft magnetic properties as a function of annealing temperatures. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dielectric and magnetic properties of citrate-route-processed Li,Co spinel ferritesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007Nutan Gupta Abstract Cobalt-substituted lithium ferrites (with general composition Li0.5,x /2CoxFe2.5,x /2O4, where x = 0.0, 0.2, 0.4, 0.5 and 0.6) were prepared at lower processing temperatures (,600 °C) by the citrate route. The single-phase spinel structure was confirmed by X-ray diffraction. The average particle size of calcined powders calculated by the Scherrer formula is estimated to be 8,90 nm, whereas an average particle size of ,20 nm is observed from TEM for Co concentration x = 0.5. Average grain sizes from SEM micrographs of pellets sintered at 1000 °C (1 h) are observed to be 0.5,1 ,m, much smaller than the size reported for the standard ceramic method (2.1,6.8 ,m). The experimental density is observed to be 3.59,4.47 gm/cm3, which is greater than 85% of the densities evaluated from XRD. Compared with the standard ceramic method, lower dielectric constant (10,103) and higher dc resistivity (105,1010 , cm) is observed for Li,Co ferrites prepared by the citrate route. Improved magnetic properties, such as higher saturation magnetization (38,79 emu g,1) and Curie temperature (535 to 620 °C) are also investigated for the citrate-route-processed samples. These results demonstrate promising features of Li,Co ferrites in microwave applications. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic study of Hitperm alloys (Fe0.5Co0.5)1,x ,y ,zMxByCuz (M = Hf, Zr, Nb)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006Abstract A family of the Hitperm alloys (Fe0.5Co0.5)1,x ,y ,zMxByCuz (M = Hf, Zr, Nb) produced in an argon atmosphere as amorphous ribbons with 0.025 mm thickness are investigated up to 1200 K. The partial replacement of Fe by Co with optimal Fe0.5Co0.5 ratio increases the Curie temperature of the amorphous phase and the magnetic moment per formula unit. The early stages of crystallization can be observed by magnetization measurements. Alloys subjected to the first controlled crystallization stage are built of bcc-(Fe,Co) nanocrystals that are homegeneously embedded in the amorphous matrix. Mean grain sizes are about 11 nm. These two-phase alloys exhibit good soft magnetic properties with the relatively low coercive fields up to 50 A/m. Hafnium and hafnium/zirconium mixture are found to be the best inhibitors of the nanograin growth resulting in the best soft magnetic parameters. Alloys with niobium exhibit lower thermal stability and higher coercive fields. The correlation between the structure evolution and the magnetic properties is analysed and discussed. Conditions for optimum heat treatment are also determined. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature dependence of magnetic microstructure in Fe76Mo8Cu1B15 nanocrystalline alloyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2004M. Miglierini Abstract Fe76Mo8Cu1B15 nanocrystalline alloy featuring close-to-room Curie temperature of 310 K proves to be suitable for model case studies of complexity of magnetic interactions. Annealed samples with different contents of nanocrystallites are characterized by 57Fe transmission Mössbauer spectrometry performed in a wide temperature range (77,673 K). The validity of the temperature dependences of hyperfine parameters is discussed for all structural components including amorphous residual phase, bcc Fe nanocrystals and interface regions located in between the former two. Cautions which must be considered in deriving information about their relative contents are pointed out, because of the presence of static and dynamic effects at high temperatures due to non-interacting and weakly interacting single domain ferromagnetic grains dispersed into a paramagnetic amorphous matrix. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electronic structure and magnetic properties of Cu-doped SnO2 from first-principles studyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2009Chang-wen Zhang Abstract We have studied the electronic structure of Cu-doped SnO2, with different possible geometrical sites for the Cu dopant, to determine the most favored magnetic properties. Our study shows that each Cu has spin-polarized states in the band gap generating a magnetic moment 2.0,B. We also find Cu impurities tend to form clusters which induces strong ferromagnetism with high Curie temperature, through the same p,d hopping interactions as found in Sr2FeMoO6 [Phys. Rev. Lett. 85, 2549 (2000)]. Doped p-type carriers enhanced the ferromagnetism, while n-type carriers are detrimental to ferromagnetism due to charge compensating effects, indicating that the strong ferromagnetism in Cu-doped SnO2 would be achieved by hole doping. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Excitons in ZnO/Zn1,xMnxO quantum wellsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2007T. Tchelidze Abstract In order to estimate the perspectives of using ZnO/Zn1,xMnxO quantum wells for reliable high temperature ferromagnetism (specially for increasing Curie temperature in this structure) we investigate excitons in ZnO/Zn1,xMnxO quantum wells. The existence of weak built-in electric field is investigated. Electric field and Coulomb interaction is accounted by means of direct diagonalization. Calculations showed weak dependence of exciton binding energy on well width. Electric field only slightly increases the distance between electron and hole. It rotates ground state excitons and aligns them along the field. Calculations also showed increase of ground state exciton lifetime with increasing well width. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of dilution and disorder on magnetism in diluted spin systemsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007Guixin Tang Abstract The influence of configurational disorder on the magnetic properties of diluted Heisenberg spin systems is studied with regard to the ferromagnetic stability of diluted magnetic semiconductors. The equation of motion of the magnon Green's function is decoupled by Tyablikov approximation. With supercell approach, the concentrations of magnetic ions are determined by the size of the supercell in which there is only one magnetic ion per supercell in our method. In order to distinguish the influence of dilution and disorder, there are two kinds of supercells being used: the diluted and ordered case and the diluted and disordered case. The configurational averaging of magnon Green function due to disorder is treated in the augmented space formalism. The random exchange integrals between two supercells are treated as a matrix. The obtained magnon spectral densities are used to calculate the temperature dependence of magnetization and Curie temperature. The results are shown as following: (i) dilution leads to increasing the averaged distance of two magnetic ions, further decreases the effective exchange integrals and is main reason to reduce Curie temperature; (ii) spatial position disorder of magnetic ions results in the dispersions of the exchange integrals between two supercells and slightly changes ferromagnetic transition temperature; (iii) the exponential damping of distance dependence obviously reduces Curie temperature and should be set carefully in any phenomenological model. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Substantial pressure effect on the resistivity and Curie temperature for the diluted magnetic semiconductor Sb2,xVxTe3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2006J. S. Dyck Abstract The influence of hydrostatic pressure on the electrical resistivity , and ferromagnetic transition temperature TC of bulk, single crystal Sb1,xVxTe3 with x = 0.03 is presented. Pressure strongly suppresses , at all temperatures, with an overall decrease of about 35% at 1.6 GPa. The peak in , , a signature of TC, moves to lower temperature with increasing pressure. An overall suppression of TC near 40% at 1.6 GPa is observed. The results are discussed within the context of a carrier-mediated ferromagnetic exchange interaction. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetotransport and magnetic properties of p -Zn1, xMnxTe:N , Carrier-induced ferromagnetismPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004K.-T. Nam Abstract The magnetic properties of nitrogen-doped p -Zn1, xMnxTe grown by MBE were studied through the magnetotransport measurements. In a sample of p -Zn1, xMnxTe with x = 0.034 and p = 4.7 × 1019 cm,3, a hysteresis loop was observed below 2.5 K in the Hall resistance and the magnetoresistivity, which indicates the ferromagnetic transition. From the plot of (RHall/Rsheet)2 against B/(RHall/Rsheet) at several temperatures, which corresponds to the so-called Arrott plot, we can estimate the Curie temperature (Tc) of the sample as about 3 K, suggesting that this sample has the higher Tc than ever reported. We also demonstrated, by means of light irradiation, that the strength of ferromagnetic interactions can be controlled by changing the hole concentration. An increase of the ferromagnetic behaviours such as a small increase of the coercive field was observed under light irradiation. This result strongly supports that the ferromagnetic transition in Zn1, xMnxTe is the carrier-induced one. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nitrides as spintronic materialsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003Tomasz Dietl The Guest Editors of the Proceedings of the 5th International Conference on Nitride Semiconductors (ICNS-5), Hiroshi Amano and Takashi Udagawa, have nominated the invited presentation by Tomasz Dietl [1] as Editor's Choice of the present issue of physica status solidi (b). This paper is a progress report on spintronics-related issues in Mn-based III-nitrides as potential diluted magnetic semiconductors. The cover picture shows the computed values of the Curie temperature for various p-type III,V compounds containing 5% of Mn in the S = 5/2 high spin state and 3.5 × 1020 holes per cm3, predicting that TC should exceed room temperature in the Mn-based nitrides. Thomas Dietl is head of the Low-Temperature Physics Group and professor at the Institute of Physics of the Polish Academy of Sciences. He is one of the most experienced researchers in the area of ferromagnetic semiconductors, spin-related phenomena and other current topics of semiconductor physics with many publications and invited talks at conferences and seminars world-wide. The full Proceedings of the 5th International Conference on Nitride Semiconductors (ICNS-5) are published in physica status solidi (c) , conferences and critical reviews, Vol. 0, No. 7 (November 2003) (ISBN 3-527-40489-9). Conference papers can also be found in phys. stat. sol. (a) 200, No. 1 (2003). [source] Dynamical CPA theory of magnetism , harmonic approximationPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003Y. Kakehashi Abstract We have developed the dynamical coherent potential approximation (CPA) to the correlated electron system on the basis of the functional integral method and the harmonic approximation. The theory becomes exact in the high temperature limit, reproduces the results of the second order perturbation theory for small Coulomb interaction, and takes into account the terms to describe the strong correlation limit. The numerical calculations show that the theory describes the Curie,Weiss susceptibility, a large reduction of the Curie temperature due to the dynamical effects, and a many-body satellite peak as well as a band narrowing in the density of states. [source] | ||||||||||||||||||||||