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To investigate ferromagnetic semiconductors and insulators, such as the famous EuO, EuS, or CrBr3, we propose a hybridized Kondo-lattice model, where, in addition to the conduction electrons, localized moments (e.g., the 4f-electi...
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To investigate ferromagnetic semiconductors and insulators, such as the famous EuO, EuS, or CrBr3, we propose a hybridized Kondo-lattice model, where, in addition to the conduction electrons, localized moments (e.g., the 4f-elections) are modeled as a strongly correlated band system. The quasi-empty conduction band is weakly filled due to the hybridization term. This activates the intraatomic exchange coupling between conduction and localized electrons. Temperature-dependent phase diagrams and quasiparticle densities of states are presented for various coupling and hybridization strengths. Moreover, the influence of the one-particle energy of the localized electrons E-f is discussed. A comparison with mean held calculations is given at the end of this work. (C) 2014 Elsevier B.V. All rights reserved.
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Large single crystals of optimally doped Eu(Fe0.91Rh0.09)(2)As-2 were grown by the self-flux method. Resistivity and magnetization measurements show that the compound undergoes a superconducting transition at 19.6 K, followed by a...
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Large single crystals of optimally doped Eu(Fe0.91Rh0.09)(2)As-2 were grown by the self-flux method. Resistivity and magnetization measurements show that the compound undergoes a superconducting transition at 19.6 K, followed by a ferromagnetic ordering of the Eu2+ moments at 16.8 K. The upper critical fields at zero temperature are estimated to be 12.5 T and 15.1 T for fields along the ab plane and the c-axis, respectively. Moreover, anisotropy reversal of the upper critical field is observed near the magnetic ordering temperature, which may be related to the anisotropic magnetization of Eu ions and the demagnetization effect. Both ferromagnetic and superconducting features are displayed by the magnetic susceptibility and peculiar isothermal magnetization loop. Our combined results unambiguously demonstrate the coexistence of ferromagnetism and superconductivity in the title compound.
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Magnetic multilayers consisting of itinerant ferromagnetic SrRuO_3 (SRO) and antiferromagnetic NiO were pulse-laser deposited on (0 0 1) SrTiO_3 substrates. After small-field cooling, enhancements from both the unconventional exch...
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Magnetic multilayers consisting of itinerant ferromagnetic SrRuO_3 (SRO) and antiferromagnetic NiO were pulse-laser deposited on (0 0 1) SrTiO_3 substrates. After small-field cooling, enhancements from both the unconventional exchange bias (EB) and the large coercive field were observed in the multilayers. Coercivity values for the in-plane hysteresis loop increased by almost 50 times in comparison with a pure SRO film. The maximum value of the bias moment in the minor loop and the EB field can be achieved in different cooling fields. Moreover, hysteresis indicates a two-step magnetization reversal. We speculate that a pinned layer exists at the SRO/NiO interface producing magnetic regions that pin the ferromagnetic SRO layer.
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We have investigated both the static and dynamic magnetic properties of rectangle antidot arrays in a ferromagnetic thin film. The thin films are FeCoBSi amorphous alloy with different thicknesses (40, 80, 160, and 320 nm) on a Si...
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We have investigated both the static and dynamic magnetic properties of rectangle antidot arrays in a ferromagnetic thin film. The thin films are FeCoBSi amorphous alloy with different thicknesses (40, 80, 160, and 320 nm) on a Si substrate. Vibrating sample magnetometry and microstrip transmission line measurements are conducted to associate the microwave magnetic analysis of the antidot arrays with hysteresis studies. The patterned films result in the change of ferromagnetic resonance from single-band to multiband, and the destruction of in-plane uniaxial anisotropy. Hence, the mechanisms of multiresonance are proposed to be related to the special domain-wall motion and spin-wave modes what is caused by the demagnetizing field in per-unit area. To study the magnetic torques in per-unit area, The Object Oriented MicroMagnetic Framework (OOMMF) is used to simulate the dynamic magnetization process.
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This study presents the decoupling of ferromagnetic properties of Fe-Co-Hf-N films with an in-plane uniaxial anisotropy from ferromagnetic cemented carbide (WC-Co) substrates by predepositing a non-ferromagnetic buffer layer betwe...
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This study presents the decoupling of ferromagnetic properties of Fe-Co-Hf-N films with an in-plane uniaxial anisotropy from ferromagnetic cemented carbide (WC-Co) substrates by predepositing a non-ferromagnetic buffer layer between the substrate and the film. Due to the ferromagnetic Co content in the substrate, a magnetic coupling effect arises which suppresses the natural ferromagnetic resonance of the Fe32Co45Hf11N12 film at a frequency of 2.13 GHz. The deposition of a non-ferromagnetic, electrically conductive TiN layer, or a non-ferromagnetic, electrically insulating SiO2 layer between the substrate and the soft ferromagnetic film shows decoupling regarding the static ferromagnetic properties, so that the formation of an in-plane uniaxial anisotropy is possible. With regard to the application as a high-frequency sensor the paper shows that with increasing the thickness of the electrically insulating SiO2 buffer layer the full width at half maximum (FWHM) of the resonance line becomes much sharper, in contrast to the electrically conductive TiN. The explanation was attributed to the formation of eddy-currents in the electrically conductive material causing a magnetic field which disturbs the uniform precession of the magnetic moments. The high-frequency properties of the decoupled film system are promising for a thermal and mechanical stress sensor system on cutting tools.
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The organic magnetic polymer has been researched and developed in the USA, Russia, Japan and other countries in recent years for its great value both in theory and practice. Ovchinnikov reported the first synthesis of pure ferroma...
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The organic magnetic polymer has been researched and developed in the USA, Russia, Japan and other countries in recent years for its great value both in theory and practice. Ovchinnikov reported the first synthesis of pure ferromagnetic organic-polymer (metal free), but the saturation magnetization (M_s) is only about one thousandth of the theoretical value. Soon afterwards, Cao et al. did a similar study. Their work is important in theory rather than in practice.
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X-ray crystal structure analyses of the 4-(4-halobenzylideneamino)TEMPO (TEMPO = 2,2,6,6-tetramethyl-piperidyl-1-oxyl) radicals 4-(4-fluorobenzylideneamino)-2,2,6,6-tetramethylpiperidyl-1-oxyl, 4-(4-chlorobenzylideneamino)-2,2,6,6...
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X-ray crystal structure analyses of the 4-(4-halobenzylideneamino)TEMPO (TEMPO = 2,2,6,6-tetramethyl-piperidyl-1-oxyl) radicals 4-(4-fluorobenzylideneamino)-2,2,6,6-tetramethylpiperidyl-1-oxyl, 4-(4-chlorobenzylideneamino)-2,2,6,6-tetramethylpiperidyl-1-oxyl, 4-(4-bromob enzylidene amino)-2,2,6,6-tetramethylpiperidyl-1-oxyl and 4-(4-iodobenzylideneamino)-2,2,6,6-tetramethylpiperidyl-1-oxyl, and other 4-Ar-CH=N-TEMPO [Ar = 4-Ph-Ph, 2,2,6,6-tetramethyl-4-(4-phenylbenzylideneamino)piperidyl-1-oxyl, 4-Py, 2,2,6,6-tetramethyl-4-(4-pyridylmethylideneamino)piperidyl-1-oxyl, and 3,5-diCl-Ph, 4-(3,5-dichlorobenzylideneamino) -2,2,6,6-tetramethylpiperidyl-1-oxyl] radicals have been performed at room temperature. Some of these radicals show intermolecular ferromagnetic interactions at extremely low temperatures. X-ray analysis revealed that crystals of the 4-I-Ph derivative showed two modifications [(a) and (b)] measurements of the magnetic properties of these crystals showed a ferromagnetic transition at an extremely low temperature for modification (a) and an antiferromagnetic interaction for modification (b). The structural features of these TEMPO radical crystals can be classified into three groups: (i) the crystal structures of the 4-Cl-Ph, 4-I-Ph(a) and 4-Ph-Ph derivatives, which show a ferromagnetic transition; (ii) the structures of the 4-Br-Ph and 4-Py derivatives, which show a ferromagnetic interaction (theta > 0); (iii) miscellaneous: the antiferromagnetic 4-F-Ph and 4-I-Ph(b) derivatives (theta < 0) and the ferromagnetic 3,5-diCl-Ph (theta > 0) derivative. Sheetlike arrangements of O atoms and intra-sheet interactions through the CH2 or CH3 groups of the TEMPO rings are related to the mechanisms of the ferromagnetic interactions. [References: 21]
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X-ray crystal structure analyses were performed on 4-(Ar-methyleneamino)-TEMPO radicals at room temperature (TEMPO = 2,2,6,6-tetramethylpiperidyl-1-oxyl): Ar = Ph [4-(benzylideneamino)-2,2,6,6-tetra-methylpiperidyl-1-oxyl], 4-MeS-...
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X-ray crystal structure analyses were performed on 4-(Ar-methyleneamino)-TEMPO radicals at room temperature (TEMPO = 2,2,6,6-tetramethylpiperidyl-1-oxyl): Ar = Ph [4-(benzylideneamino)-2,2,6,6-tetra-methylpiperidyl-1-oxyl], 4-MeS-Ph [2,2,6,6-tetramethyl-4-(4-methylthiobenzylideneamino)piperidyl-1-oxyl], 4-Me-Ph [4-(4-methylbenzylideneamino)-2,2,6,6-tetramethylpiperidyl-1-oxyl], 4-PhO-Ph [2,2,6,6-tetramethyl-4-(4-phenoxybenzylideneamino)piperidyl-1-oxyl], 4-MeSO2-Ph [2,2,6,6-tetramethyl-4-(4-methylsulfonylbenzylideneamino)piperidyl-1-oxyl] , 3-Py [2,2,6,6-tetramethyl-4-(3-pyridylmethylideneamino)piperidyl-1-oxyl] and 2-Naph [2,2,6,6-tetramethyl-4-(2-naphthylideneamino)piperidyl-1-oxyl]. Structures of Ph and 4-Me-Ph derivatives were also determined at 100 K. Some of these crystals have been revealed to show intermolecular ferromagnetic interactions at an extremely low temperature. Structural features of crystals of Ph, 4-MeS-Ph and 3-Py derivatives, which show ferromagnetic interactions, are very similar to each other. In these crystals, O atoms are arranged to form a sheet. The ferromagnetic interactions are considered to be transferred through O ... H van der Waals' interactions of the B-H atoms of the neighboring TEMPO rings within the sheet. Between O ... O sheets, the aryl groups are arranged in a herringbone manner. The crystal structure of the 4-Me-Ph derivative, which shows an antiferromagnetic interaction, is also pseudo-isostructural with those of Ph, 4-MeS-Ph and 3-Py derivatives, while the arrangement of the aryl groups is different. The packing mode of the crystals of the 4-MeSO2-Ph derivative, of which the Weiss constant theta is nearly zero, is very different from those of the other derivatives showing magnetic interactions. The fact that the crystal structure of the paramagnetic 4-MeSO2-Ph derivative does not show the O ... O sheet structure accompanying the O ...beta-H interactions indicates that the intermolecular ferromagnetic interactions through B-H atoms within the O ... O sheet are important for these TEMPO radical crystals. [References: 20]
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Superlattices consisting of ferromagnetic SrRuO3 and superconducting YBa2Cu3O7 [YBCO] layers of a thickness between 5 urn and 60 nm have been analyzed with respect to their magnetic [T-mag] as well superconducting [T-C] ordering t...
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Superlattices consisting of ferromagnetic SrRuO3 and superconducting YBa2Cu3O7 [YBCO] layers of a thickness between 5 urn and 60 nm have been analyzed with respect to their magnetic [T-mag] as well superconducting [T-C] ordering temperature. The reduction of both is compared with previous results obtained in YBCO/La2/3Ca1/3MnO3 superlattices. Whereas the reduction of T-C is comparable for both ferromagnetic materials the suppression of ferromagnetism is more pronounced in the case of the SrRuO3-based superlattices. This result is discussed in terms of a competition of the order parameters giving rise to ferromagnetism and superconductivity and the role of interface roughness. [References: 4]
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Rapid advances in controlled preparation techniques have enabled us to fabricate submicron-scale magnetic structures. Considerable interest has been paid to the spin-excitation spectrum of a small magnetic structure. Several exper...
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Rapid advances in controlled preparation techniques have enabled us to fabricate submicron-scale magnetic structures. Considerable interest has been paid to the spin-excitation spectrum of a small magnetic structure. Several experiments using ferromagnetic resonance absorption or Brillouin light scattering have been performed to probe how the reduction of sample size affects the spin-excitation spectrum. The measurement in these experiments is carried out for arrays of small samples. Thus, strictly speaking, the results do not reveal the spectrum of individual samples. Besides the dynamical magnetic properties, electron transport properties in mesoscopic ferromagnetic metals have been the subject of intesive study. Particularly, the magnetoresistance of thin wires containing a magnetic domain wall (DW) has attracted attention with the aim of studying DW dynamics. It has been shown that we can detect DW depinning by measuring the resistance as a function of a magnetic field. Furthermore, it it shown recently that the dynamical property of a DW can be studied by measuring the magnetoresistance. These studies suggest that the magnetoresistance of various magnetic structures may provide us useful informations on their dynamical property.
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