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Coercive Field (coercive + field)
Selected AbstractsGiant Coercive Field of Nanometer- Sized Iron Oxide,ADVANCED MATERIALS, Issue 1 2004J. Jin Nanocrystals of iron oxide in a silica matrix exhibiting a giant Hc value of 2.0,T at room temperature are reported. The nanocomposite was obtained by combining reverse-micelle and sol,gel methods. The nanocrystals of iron oxide are composed of the ,-Fe2O3 phase, with rod-like particles 100,140,nm long and 20,40,nm wide. The Figure shows the hysteresis curve of the nanocrystals. [source] Strength Properties of Poled Lead Zirconate Titanate Subjected to Biaxial Flexural Loading in High Electric FieldJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Hong Wang The mechanical strength of poled lead zirconate titanate (PZT) has been studied using ball-on-ring (BoR) biaxial flexure tests with a high electric field applied concurrently. Both the as-received and the aged PZT specimens were tested. The Weibull plot and a 95% confidence ratio ring were used to characterize the responses of mechanical strength under various electric loading conditions. A fractographical study has been conducted at the same time, and the fracture origins or strength-limiting flaws of tested PZT specimens have been identified and characterized accordingly. The fracture toughness was further estimated to correlate with the obtained fracture stresses and flaws. It has been observed that electric field affects the mechanical strength of poled PZT, and the degree of the effect depends on the sign and magnitude of the applied electric field. Within the examined electric field range of ,3 to +3 times the coercive field, an increasing electric field resulted in a rapid strength decrease and a sharp increase with the turning point around the negative coercive field. Surface-located volume-distributed flaws were identified to be strength limiting for this PZT material. Variations of the mechanical strength with the electric field were believed to be related to the domain switching and amount of switchable domains. An aging effect on the mechanical strength of poled PZT could be significant, especially in the OC condition. These results and observations have the potential to serve probabilistic reliability analysis and design optimization of multilayer PZT piezo actuators. [source] Bilayered BiFe0.95Mn0.05O3/Bi0.90La0.10FeO3 Thin Films with Low Ferroelectric Coercivity and Large Remanent PolarizationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Jiagang Wu Bilayered thin films consisting of (Bi0.90La0.10)FeO3 and Bi(Fe0.95Mn0.05)O3, i.e., Bi(Fe0.95Mn0.05)O3/(Bi0.90La0.10)FeO3, were deposited on SrRuO3 buffered SrTiO3(111) substrates by off-axis radio frequency magnetic sputtering, where (111)-oriented bilayered thin films were obtained. The bilayered Bi(Fe0.95Mn0.05)O3/(Bi0.90La0.10)FeO3 thin film possesses a lower coercive field (2Ec,335.6 kV/cm) and a larger remanent polarization (2Pr,155.2 ,C/cm2) at room temperature, and a higher relative permittivity as compared with those of single-layer (Bi0.90La0.10)FeO3 and Bi(Fe0.95Mn0.05)O3 thin films, together with an improvement of the magnetic properties (2Ms,31.2 emu/cm3). The bottom (Bi0.90La0.10)FeO3 nanolayer promotes the growth of the Bi(Fe0.95Mn0.05)O3 layer, which are largely responsible for the multiferroic behavior observed. [source] Structural and Electrical Properties of Er2O3 -Doped Na1/2Bi1/2TiO3 Lead-Free PiezoceramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Mengjia Wu Sodium bismuth titanates Na1/2Bi1/2TiO3 (NBT) doped with 0,3 wt% Er2O3 were prepared by the conventional solid-state reaction method. The X-ray diffraction results revealed that the sintered Er-doped NBT ceramics exhibited a pure perovskite structure with Er3+ concentrations ranging from 0 to 1 wt%. At a low Er2O3 concentration, the Er-doped NBT ceramics showed enhanced electrical properties with dielectric constant ,33T/,0=636, a low dielectric dissipation factor (tan ,=3.3%), a low coercive field (Ec=4.56 kV/mm), and a high piezoelectric constant (d33=75 pC/N). The relationship between the composition and properties of Er-doped NBT ceramics has been discussed. [source] Structural and Electric Properties of Sol,Gel-Derived Ba0.9Sr0.1TiO3 MultilayersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007X. K. Hong Crack-free Ba0.9Sr0.1TiO3 (BST) and Mn-doped Ba0.9Sr0.1TiO3 (BSTM) multilayers with thickness over 2 ,m have been prepared by chemical solution deposition based on one single precursor. Both multilayers exhibit good performance as Bragg reflectors. Mn doping tends to suppress the leakage current in BST multilayers effectively by smoothing the layers and the reduction of the charge carries. The Mn-doped BST multilayer displays an excellent ferroelectric property, with an average remnant polarization (Pr+,Pr,)/2 of 12.69 ,C/cm2 and an average coercive field (E+,E,)/2 of about 72.95 kV/cm under an applied field of 440 kV/cm. [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 Field Simulations of Hysteresis and Butterfly Loops in Ferroelectrics Subjected to Electro-Mechanical Coupled LoadingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006A. K. Soh Two-dimensional computer simulations of ferroelectric polarization switching have been performed using the phase field simulation model developed by employing the time-dependent Ginsburg,Landau equations. The bulk-free energy, polarization gradient energy, long-range dipole,dipole electrostatic interactions, and elastic energy were taken into account in the above-mentioned simulations. The influences of electric,mechanical coupled loading on the hysteresis and butterfly loops were studied. The results showed that the coupled electro-mechanical loading could change both the coercive field of ferroelectric materials and the symmetry of hysteresis and butterfly loops. [source] Analysis of magnetic properties in patterned micro-NiFe elements with micro-MOKE and micromagneticsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004K. C. Kim Abstract Magnetic properties of a patterned micro-NiFe element were analyzed with micro-MOKE and micromagnetics. Patterned 8 ,m × 16 ,m NiFe elements have higher coercive field, Hc = 1.9 Oe, for the hard axis than that, Hc = 0.2 Oe, of a 5 mm diameter disk NiFe sample. The magnetization reversal processes have been investigated with the micromagnetic simulation for the various applied field directions. The increase of coercive field in patterned micro-NiFe elements can be attributed to the large shape anisotropy and pinned spins along the edges. Total anisotropy of a 8 ,m × 16 ,m NiFe sample was about 50 Oe. The magnetization reversal field of pinned spins along the edges in patterned micro-NiFe sample was about 500 Oe. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic properties of Fe76X2B22 (X=Cr,Zr,Nb) amorphous alloysPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003A. Chrobak Abstract The paper contains experimental results referring to optimization of soft magnetic properties and crystallization in the Fe76X2B22 (X=Cr,Zr,Nb) amorphous alloys. We have used measurement of thermomagnetic balance, magnetic permeability, coercive field and also HREM and X-ray diffraction techniques. It was shown that Zr and Nb alloying additions cause a slowing down of diffusion processes and an increase of the annealing for 1 hour optimization temperature of about 50 and 100 K, respectively. Activation enthalpies of the crystallization process were determined as: 2.0 eV (X=Cr), 2.6 eV (X=Zr) and 4.4 eV (X=Nb). [source] The influence of dipolar interaction on magnetic properties in nanomagnets with different shapesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2010Ying Li Abstract With the Monte Carlo method, we investigate the magnetic properties of four nanomagnets of different shapes, i.e., the circular-shaped, the square-shaped, the elliptical, and the ring-shaped nanomagnets. A systematic study of the effects of the dipolar interaction on the magnetic configurations is performed in these nanomagnets, and further the coercive field and the remanence as a function of dipolar interaction are analyzed. The results show that the magnetic configuration and thus the magnetization reversal process of nanomagnets are dependent strongly on the strength of dipolar interactions. For the case of small dipolar interaction, the magnetization reversal process is mainly dominated by spin rotation, while the reversal transforms to the vortex nucleation and propagation formations with increasing dipolar interaction. Moreover, if the dipolar interaction is neglected in the calculation of the total energy, no clear difference is found among hysteresis loops of four nanomagnets with same areas, but the inclusion of dipolar interaction can lead to different hysteresis loops for nanomagnets with same areas but different shapes. This indicates that the dipolar interaction is important for accounting for the shape effect of the magnetic properties in nanomagnets. [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] Oxidation-induced high-Curie-temperature ferromagnetism in CoAl(100)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2007V. Rose Abstract In conventional magnetic materials, oxidation is a disagreeable effect that often lowers or destroys the magnetic capabilities of those materials. By contrast, we report on the decisive paramagnetic-ferromagnetic phase transition in CoAl(100) at room temperature, utilizing oxidation of stoichiometric CoAl. We also discuss the control and drastic increase of the coercive field by subsequent annealing of the oxidized sample. The alumina film grown by selective oxidation protects the alloy from oxidation of Co, despite the accumulation of Al vacancies and the resulting enrichment in Co of the metallic phase underneath the oxide film. As a result, a ferromagnetic thin Co-rich phase is formed at the interface between the insulating aluminum oxide and the paramagnetic Co50Al50 bulk. The creation via simple oxidation of a ferromagnetic thin film underneath a surface insulator demonstrates a novel path to building the majority of a magnetic tunnel junction. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pinning energy of domain walls in MnZn ferrite filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2007V. H. Calle Abstract Mn Zn ferrite films deposited on (100) MgO substrates by rf sputtering technique with different thicknesses , in the range of 30-450 nm were studied. AFM images show grain size increase as film thickness increases. Grains with diameters between L , 70 and 700 nm were observed. The mono and multidomain regime in MnZn ferrite films and their effect on the pinning energy of domain walls are observed via Magneto-optical Kerr Effect, MOKE. At , , 300 nm, the coercive field, Hc, reaches a maximum value of 80 Oe. This result indicates the existence of a multidomain regime associated to a critical grain size, Lc. We used the Jiles-Atherton model (JAM) to discuss the experimental hysteresis loops. The k pinning parameter obtained from JAM shows a maximum value of k /,o = 67 Am2 for grains with Lc , 529 nm. The total energy per unit area E was correlated with k and D. We found a simple phenomenological relationship given by E , kD; where D is the magnetic domain width. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic properties of ultra-thin epitaxial V/Gd bilayersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2004P. Pankowski Abstract Magnetic properties of a new system of epitaxial vanadium/gadolinium bilayers with different V thickness have been studied. The structure and quality of bilayers was determined by X-ray reflectivity measurements using synchrotron radiation. Hysteresis loops measurements suggest in-plane anisotropy for all samples (Mr/Ms close to 1). Basic magnetic properties: saturation magnetisation, coercive field and remanence were obtained. Average magnetic moment analysis gives a possibility of an induced magnetic moment on vanadium atoms. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A New Chiral Schiff Base with Ferroelectric PropertyCHINESE JOURNAL OF CHEMISTRY, Issue 11 2008Xiu-Zhi LI Reaction of 1,1,1,5,5,5-hexafluoropen- tane-2,4-dione with (1S,2S)-(,)-1,2-diaminocyclohexane afforded a chiral Schiff base (1Z,4Z)-2,4-bis(trifluoromethyl)-5a,6,7,8,9,9a -hexahydro-3H -benzo[b][1,4]diazepine (1). Fluorescent analysis showed its intense emission band at 488 nm when the exciting radiation was set at 437 nm. Crystallographic analysis shows that it belongs to a non-centric space group C2 with ferroelectric behavior. A typical ferroelectric feature of electric hysteresis loop was obtained, with remanent polarization (Pr) of ca. 0.01 µC/cm2 and coercive field (Ec) of 0.27 kV/cm. [source] Hybrid Magnetic Materials Based on Nitroxide Free Radicals and Extended Oxalato-Bridged Bimetallic NetworksEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2005Antonio Alberola Abstract A series of hybrid organic-inorganic magnets of formula p -rad[MIICr(ox)3] [M = Mn (1), Co (2), Ni (3), Zn (4)] and m -rad[MIICr(ox)3] [M = Mn (5), Co (6)], in which N -methylpyridinium cations bearing a nitronyl nitroxide moiety in positions 3 (m -rad) or 4 (p -rad) of the pyridine ring coexist with the 2D honeycomb-like oxalato-bridged bimetallic lattice, has been prepared and studied by AC and DC magnetic susceptibility measurements and EPR spectroscopy. In general, the physical properties of these magnets are not altered significantly by the insertion of the nitronyl nitroxide radicals although these paramagnetic molecules seem to interact weakly with the inorganic network as demonstrated by EPR spectroscopy. Some differences can also be observed between the p -rad and m -rad series, i.e. m -rad derivatives have smaller values for the critical temperatures and coercive fields. We also report on the X-ray crystal structures and magnetic properties of p -rad[Mn(H2O)Cr(ox)3]·2H2O (7) and m -rad[Mn(H2O)2Cr(ox)3]·2H2O (8), two extended oxalato-bridged compounds with new topologies. Compound 7 is antiferromagnetic and its structure is a 3D achiral lattice in which zigzag ferromagnetic MnCr chains (J/k = +0.8 K) are interconnected to form hellicoidal hexagonal channels with the cationic free radicals residing in the free space. Compound 8, however, exhibits a ladder-like structural pattern with competing magnetic interactions and paramagnetic behaviour down to low temperatures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [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] | ||||||||||||||||