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Magnetic System (magnetic + system)
Selected AbstractsMagnetoelectric Effects in Complex Oxides with Competing Ground StatesADVANCED MATERIALS, Issue 34 2009Hajo J. A. Molegraaf Direct, charge-mediated magnetoelectric coupling is demonstrated in a heterogeneous multiferroic that takes advantage of the sensitivity of a strongly correlated magnetic system to competing electronic ground states. Using magneto-optic Kerr effect magnetometry, we observe large magnetoelectric coupling in ferroelectric/lanthanum manganite heterostructures, resulting in control of the magnetic state by means of an applied electric field, as illustrated in the figure. [source] Design and application of layered composites with the prescribed magnetic permeabilityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2010Jae Seok Choi Abstract This research aims to design the microstructure with the prescribed magnetic permeability and proposes a design method to control the magnetic flux flow using layered microstructures. In the optimization problem for the microstructure design, the objective function is set up to minimize the difference between the homogenized magnetic permeability during the design process and the prescribed permeability based on the so-called inverse homogenization method. Based on the microstructure design result, a microstructure composed of layered materials is proposed for the purpose of the efficient magnetic flux control. In addition, its analytical calculation is added to confirm the feasibility of the optimized results. The layered composite of a very thin ferromagnetic material is expected to guide the magnetic flux and the performance of the magnetic system can be improved by turning the microstructures appropriately. Optimal rotation angles of microstructures are determined using the homogenization design method. The proposed design method is applied to an example to confirm its feasibility. Copyright © 2009 John Wiley & Sons, Ltd. [source] Self-organization and finite size effects in epitaxial ferromagnetic MnAs films on GaAsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2007L. Däweritz Abstract The self-organized striped structure of coexisting ,-MnAs and ,-MnAs, characteristic for MnAs films grown on GaAs(001) by molecular beam epitaxy under As-rich conditions at low temperature, has been studied in samples prepared under conditions closer to the equilibrium. Whereas the period of the stripe pattern is independent on the preparation procedure, the width of the ferromagnetic ,-MnAs stripes increases. Thus, the aspect ratio p between the stripe width L and the stripe thickness t can be varied over a wide range. The magnetic properties of the finite-size magnetic system are investigated as a function of the ratio p at room temperature. The transition from type-I domains with meander-like contrast in the magnetic force microscopy (MFM) image to type-II domains with a line-shaped contrast due to the division of the stripe into N subdomains across the stripe occurs at p ratios expected from a model based on the shape anisotropy. Besides the well-known N = 3 type-II domains also type-II domains with N = 4, 5 were detected. When the stripe width approaches the period of the self-organized structure, the boundary between two neighboring stripes is imaged as chessboard-like contrast in the MFM pattern. The shape of the magnetic hysteresis loops changes with the p ratio or, in other words, with the predominance of in-plane or out-of plane magnetic moments in the demagnetized state. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Four-sublattice ferrimagnetic systems: I. Quantum fluctuations of spins at zero temperaturePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2004Rong-ke Qiu Abstract Within the framework of the linear spin wave approximation, the quantum fluctuations of spins at zero temperature in four-sublattice ferrimagnetic systems are studied by employing retard Green's functions. The effects of exchange constants on the quantum fluctuations of spins are discussed for three different spin-configurations. The magnetic properties of these spin configurations are related to their magnetically structural symmetry. When the parameters of the exchange couplings are adjusted, the crossover of the spin configurations results in the strong quantum fluctuations, owing to the behaviors of the non-three-dimensional magnetically system. When two of the four exchange-constants in the present four-sublattice bulk systems are set to be zero, the system behaves as a non-three-dimensionally magnetic system, although the structure of the system is still three-dimensional. All the exchange couplings involve in the quantum competition of the systems, but the effects of antiferromagnetic and ferromagnetic exchange couplings are different evidently. The antiferromagnetic exchange couplings play an important role in a balance of the quantum competition. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Construction of a Novel Topological Frustrated System: A Frustrated Metal Cluster in a Helical SpaceCHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2010Ryuta Ishikawa Abstract A novel topologically frustrated pentanuclear cluster helicate [{CuII(,-L)3}2CuII3(,3 -OH)]3+ (L,=3,5-bis(2-pyridyl)pyrazolate) has been synthesized and characterized. This cluster has a helical arrangement of ligands around the central metal core. Dzyaloshinsky,Moriya interactions are essential components to observe a gradual magnetization and forbidden transitions of high-field/multi-frequency (HF/MF)-ESR. The origin of the magnetic anisotropy of this compound is influenced by its helical spin structure, and consequently, the Cu5 -cluster helicate introduces a unique magnetic anisotropy. This observation is a direct evidence of the topological part of the new spin phase in a magnetic system. [source] Metal,Organic Perovskites: Synthesis, Structures, and Magnetic Properties of [C(NH2)3][MII(HCOO)3] (M=Mn, Fe, Co, Ni, Cu, and Zn; C(NH2)3= Guanidinium)CHEMISTRY - A EUROPEAN JOURNAL, Issue 44 2009Ke-Li Hu Abstract We report the synthesis, crystal structures, and spectral, thermal, and magnetic properties of a family of metal,organic perovskite ABX3, [C(NH2)3][MII(HCOO)3], in which A=C(NH2)3 is guanidinium, B=M is a divalent metal ion (Mn, Fe, Co, Ni, Cu, or Zn), and X is the formate HCOO,. The compounds could be synthesized by either diffusion or hydrothermal methods from water or water-rich solutions depending on the metal. The five members (Mn, Fe, Co, Ni, and Zn) are isostructural and crystallize in the orthorhombic space group Pnna, while the Cu member in Pna21. In the perovskite structures, the octahedrally coordinated metal ions are connected by the anti,anti formate bridges, thus forming the anionic NaCl-type [M(HCOO)3], frameworks, with the guanidinium in the nearly cubic cavities of the frameworks. The Jahn,Teller effect of Cu2+ results in a distorted anionic Cu,formate framework that can be regarded as Cu,formate chains through short basal CuO bonds linked by the long axial CuO bonds. These materials show higher thermal stability than other metal,organic perovskite series of [AmineH][M(HCOO)3] templated by the organic monoammonium cations (AmineH+) as a result of the stronger hydrogen bonding between guanidinium and the formate of the framework. A magnetic study revealed that the five magnetic members (except Zn) display spin-canted antiferromagnetism, with a Néel temperature of 8.8 (Mn), 10.0 (Fe), 14.2 (Co), 34.2 (Ni), and 4.6,K (Cu). In addition to the general spin-canted antiferromagnetism, the Fe compound shows two isothermal transformations (a spin-flop and a spin-flip to the paramagnetic phase) within 50,kOe. The Co member possesses quite a large canting angle. The Cu member is a magnetic system with low dimensional character and shows slow magnetic relaxation that probably results from the domain dynamics. [source] Supramolecular Photomagnetic Materials: Photoinduced Dimerization of Ferrocene-Based Polychlorotriphenylmethyl RadicalsCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2004Imma Ratera Abstract New ferrocenyl Schiff-base polychlorotriphenylmethyl radicals have been synthesized and characterized. The imino group of one such radical undergoes an irreversible trans to cis structural isomerization induced by light. Such photoinduced isomerization has been monitored by UV/Vis and ESR spectroscopy and also monitored by HPLC. ESR frozen solution experiments at low temperature revealed that the cis isomer dimerizes, showing a strong antiferromagnetic interaction. Although numerous photochromic supramolecular systems have been described, such a photoinduced self-assembly process represents the first example of a one-way photoswitchable magnetic system in which a conversion between a doublet and a singlet ground state species is promoted by a photoinduced dimerization process driven by the formation of hydrogen bonds. DFT calculations on the minimized structure and on the rotational barriers have been performed to establish the origin of such behavior. The effect of the substituents and the media polarity on the photoisomerization of this imine chromophore have also been studied. It has been observed that the efficiency of the process is markedly dependent on the presence and characteristics of electron-donor and electron-acceptor substituents of the ferrocenyl Schiff-base polychlorotriphenylmethyl radicals as well as on the polarity of the solvent. Han estat sintetitzats i caracteritzats nous radicals policlorotrifenilmetílics connectats a una unitat de ferrocè mitjançant una base de Schiff. El grup imino d,un d,aquests radicals experimenta una isomerització estructural irreversible de trans a cis mitjançant la llum. Aquesta isomerització fotoinduïda ha estat seguida amb les tècniques d, UV/Vis, espectroscòpia de RPE així com també mitjançant cromatografia d, HPLC. L,espectre de RPE d,una solució congelada revel.la que L,isòmer cis dimeritza mostrant una forta interacció antiferromagnètica entre monòmers. Malgrat els nombrosos sistemes supramoleculars fotocròmics que han estat descrits fins ara, aquest procés d,autoassemblatge fotoinduït representa el primer exemple d,interruptor magnètic fotoinduït d,un sol sentit en el qual té lloc una conversió de doblet a singlet de L,espècie en estat fonamental promoguda per un procés d,autoassemblatge mitjançant la formació d,enllaços d,hidrogen. S,han realitzat càlculs de DFT de les estructures minimitzades i de les barreres rotacionals per tal de poder establir L,origen d,aquest comportament. També s,ha estudiat L,efecte dels substituents i de la polaritat del medi en la fotoisomerizació d,aquests cromòfors d,imina. S,ha observat que L,eficiència del procés té una dependència molt marcada amb la presència de substituents electro donadors així com també amb la polaritat del dissolvent. [source] Performance of plane-wave-based LDA+U and GGA+U approaches to describe magnetic coupling in molecular systems,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2009Pablo Rivero Abstract This work explores the performance of periodic plane wave density functional theory calculations with an on-site Coulomb correction to the standard LDA and GGA exchange-correlation potential,commonly used to describe strongly correlated solids,in describing the magnetic coupling constant of a series of molecular compounds representative of dinuclear Cu complexes and of organic diradicals. The resulting LDA+U or GGA+U formalisms, lead to results comparable to experiment and to those obtained by means of standard hybrid functionals provided that the value of the U parameter is adequately chosen. Hence, these methods offer an alternative efficient computational scheme to correct LDA and GGA approaches to adequately describe the electronic structure and magnetic coupling in large molecular magnetic systems, although at the expenses of introducing an empirical (U) parameter. For all investigated copper dinuclear systems, the LDA+U and GGA+U approaches lead to an improvement in the description of magnetic properties over the original LDA and GGA schemes with an accuracy similar to that arising from the hybrid B3LYP functional, by increasing the on-site Coulomb repulsion with a moderate U value. Nevertheless, the introduction of an arbitrary U value in the 0,10 eV range most often provides the correct ground-state spin distribution and the correct sign of the magnetic coupling constant. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Corrosion of Dental Magnet Attachments for Removable Prostheses on Teeth and ImplantsJOURNAL OF PROSTHODONTICS, Issue 4 2009Arne F. Boeckler DMD, Dr Med Dent Abstract Purpose: For a long time, the use of magnets for the anchorage of dental prostheses failed due to lack of biocompatibility and the magnets' high susceptibility to corrosion in the mouth. These facts make encapsulation of the magnetic alloy with a corrosion-resistant, tight, and functionally firm sealing necessary. Due to different products and analysis methods, it is not feasible to compare the findings for contemporary products with the sparse and rather old test results in the literature. Therefore, the aim of this study was the standardized control and the comparison of the corrosion behavior of modern magnetic attachments for use on teeth and dental implants. Materials and Methods: Thirty-seven components of magnetic attachments on implants and natural teeth from different alloys (NdFeB, SmCo, Ti, CrMoMnTiFe, etc.) as delivered by the manufacturers or fabricated according to their instructions were examined for their corrosion behavior using the statical immersion analysis (ISO 10271:2001). Four specimens of every product with the same design were used. An uncased SmCo magnet served as control. Analyses after 1, 4, 7, and 28 days of the storage in corrosion solution were made. The eluate was examined quantitatively on the alloy components of the respective component with the help of optical emission spectrometry (,g/cm2). The results were compared to the requirements of ISO standard 22674:2006. In addition, existing corrosion products were also defined in the solution after 28 days. The results were analyzed descriptively and statistically to determine possible significant differences (t -test and Mann-Whitney-Wilcoxon rank-sums test; p < 0.05). Results: Dissolved metal ions could be found on all tested products. The release after 1 and 4 days was different for all specimens. In the group of implant abutments, the highest ion release after 7 days was found (all measurements ,g/cm2): Fe (13.94, Magfit-IP-IDN dome type), Pd (1.53, Medical-anchor), Cr (1.32, Magfit-IP-IDN dome type), Ti (1.09, Magfit-IP-IDN abutment), Co (0.81, Medical-anchor), and B (0.6, Magfit-IP-IDN dome type). After 28 days, the analyzed ion release increased irregularly: Fe (173.58, Magfit-IP-IDN dome type), Pd (44.17, Medical-anchor), Cr (2.02, Magfit-IP-IDN dome type), Ti (2.11, Magfit-IP-IDN abutment), Co (26.13, Medical-anchor), B (1.77, Magfit-IP-IDN dome type), and Nd (79.18, Magfit-IP-IDN dome type). In the group of magnetic systems on natural teeth, the highest ion release after 7 days was found for Fe (4.81, Magfit DX 800 keeper), Cr (1.18, Magfit DX 800 keeper), Pd (0.21, Direct System Keeper), Ni (0.18, WR-Magnet S3 small), Co (0.12, Direct System Keeper), and Ti (0.09, Magna Cap , Mini). After 28 days, the analyzed ion release increased non-uniformly: Fe (31.92, Magfit DX 800 Keeper), Cr (6.65, Magfit DX 800 Keeper), Pd (18.19, Direct System Keeper), Ni (0.61, WR-Magnet S3 small), Co (10.94, Direct System Keeper), Ti (0.83, Magna Cap , Mini), and Pd (2.78, EFM Alloy). In contrast, the uncased control magnet showed an exponential release after 7 days of Sm ions (55.06) and Co-ions (86.83), after 28 days of Sm ions (603.91) and Co ions (950.56). The release of corrosion products of all tested products stayed significantly under the limit of 200 ,g/cm2 (ISO 22674:2006). In contrast, the non-encapsulated control magnet exceeded that limit significantly. Conclusion: The analysis of the corrosion behavior of modern magnetic attachments for use on teeth and dental implants according to ISO 10271:2001 showed that metal ions had dissolved on all specimens. In the case of one product, the magnet corroded. For this product, an improvement of the capsulation would be desirable. None of the products reached the limit specified in ISO 22674:2006. All products seem to be suitable for dental application. Further studies in regard to the specific biocompatibility and possible cytotoxic effects on mucosa and tissue would be desirable. [source] Mechanical Properties of Magnetic Attachments for Removable Prostheses on Teeth and ImplantsJOURNAL OF PROSTHODONTICS, Issue 8 2008Arne F. Boeckler DMD Abstract Purpose: Magnetic attachments on teeth and implants may be used to improve stability, support, and retention of removable prostheses. Various forms of magnetic attachments are available, divided according to the design, the mechanical properties of the attachments, and the clinical indication. Recently developed attachment systems are small and promise improved retentive capacity, while existing magnetic attachments continue to be technologically modified and improved. This investigation reviewed and compared maximum retentive forces and characteristic curves for magnetic attachments indicated for use as root anchors and on implants. Materials and Methods: Twenty-four samarium-cobalt (SmCo) and neodym-iron-boron (NeFeB) magnetic attachments (12 tooth- and 12 implant-borne) were evaluated. Specimens were delivered by the manufacturers or fabricated according to their instructions. Five magnet pairs of each product and each combination were tested 10 times in a calibrated universal testing machine using a nonmagnetic test device (s = 40 mm, v = 20 mm/min). Results were recorded electronically and compared to manufacturers' details. Results: Maximum retentive forces for root keepers ranged from 1.4 to 6.6 N. Maximum retentive forces for magnetic attachments on implants ranged from 0.7 to 5.8 N. After a distance of 0.1 mm, a complete reversed distribution of the different systems became obvious. The retentive force provided by the manufacturer was achieved in one implant abutment, with retentive force (as compared to those provided by the manufacturers) for root keepers ranging between 42.5% and 92.9% and for implant abutments between 43.0% and 99.4%. Conclusion: There were differences between magnetic attachments for both the initial retentive capabilities and the characteristic curves. Recently introduced products provided relatively high initial retentive forces despite their small size. The measured retentive forces and the manufacturer's information differed in the majority of magnetic systems evaluated. [source] Proximity magnetoresistance in Ag70Fe30 and Ag74Fe26 cosputtered granular filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004P. Allia Abstract Granular films of composition Ag70Fe30 and Ag74Fe26 were prepared by dc plasma sputtering deposition in Ar atmosphere on Si substrates. Magnetization and magnetoresistance were measured between 2 K and 270 K. Both films exhibit a negative magnetoresistance (MR). The MR vs. reduced magnetisation curves are characterised by a box-like behavior, as already observed in magnetic systems with competing interactions. A standard analysis indicates that in both systems individual Fe nanoparticles are magnetically correlated over large distances. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||