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1.
Co1−xZnxFe2O4 (with x varying from 0 to 0.7) nanoparticles to be used for ferrofluid preparation were prepared by chemical co-precipitation method. The fine particles were suitably dispersed in transformer oil using oleic acid as the surfactant. The magnetization (Ms) and the size of the particles were measured at room temperature. The magnetization (Ms) was found to decrease with the increase in zinc substitution. The magnetic particle size (Dm) of the fluid was found to vary from 11.19 to 4.25 nm decreasing with the increase in zinc substitution. 相似文献
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Taner Yildirim 《Physica C: Superconductivity and its Applications》2009,469(9-12):425-441
We present a detailed first-principles study of Fe-pnictides with particular emphasis on competing magnetic interactions, structural phase transition, giant magneto–elastic coupling and its effect on phonons. The exchange interactions Ji,j(R) are calculated up to ≈12 Å from two different approaches based on direct spin-flip and infinitesimal spin-rotation. We find that Ji,j(R) has an oscillatory character with an envelop decaying as 1/R3 along the stripe-direction while it is very short range along the diagonal direction and antiferromagnetic. A brief discussion of the neutron scattering determination of these exchange constants from a single crystal sample with orthorhombic-twinning is given. The lattice parameter dependence of the exchange constants, dJi,j/da are calculated for a simple spin-Peierls like model to explain the fine details of the tetragonal–orthorhombic phase transition. We then discuss giant magneto–elastic effects in these systems. We show that when the Fe-spin is turned off the optimized c-values are shorter than experimental values by 1.4 Å for CaFe2As2, by 0.4 Å for BaFe2As2, and by 0.13 Å for LaOFeAs. We explain this strange behavior by unraveling surprisingly strong interactions between arsenic ions, the strength of which is controlled by the Fe-spin state through Fe–As hybridization. Reducing the Fe-magnetic moment, weakens the Fe–As bonding, and in turn, increases As–As interactions, causing a giant reduction in the c-axis. These findings also explain why the Fe-moment is so tightly coupled to the As-z position. Finally, we show that Fe-spin is also required to obtain the right phonon energies, in particular As c-polarized and Fe–Fe in-plane modes that have been recently observed by inelastic X-ray and neutron scattering but cannot be explained based on non-magnetic phonon calculations. Since treating iron as magnetic ion always gives much better results than non-magnetic ones and since there is no large c-axis reduction during the normal to superconducting phase transition, the iron magnetic moment should be present in Fe-pnictides at all times. We discuss the implications of our results on the mechanism of superconductivity in these fascinating Fe-pnictide systems. 相似文献
4.
J. Fortágh H. Ott S. Kraft A. Günther C. Zimmermann 《Applied physics. B, Lasers and optics》2003,76(2):157-163
In this article, we describe an experimental system for generating Bose–Einstein condensates and controlling the shape and
motion of a condensate by using miniaturised magnetic potentials. In particular, we describe the magnetic trap setup, the
vacuum system, the use of dispenser sources for loading a high number of atoms into the magneto-optical trap, the magnetic
transfer of atoms into the microtrap, and the experimental cycle for generating Bose–Einstein condensates. We present first
results on outcoupling of condensates into a magnetic waveguide and discuss influences of the trap surface on the ultra-cold
ensembles.
Received: 21 August 2002 / Revised version: 10 December 2002 / Published online: 26 February 2003
RID="*"
ID="*"Corresponding author. Fax: +49-7071/295-829, E-mail: fortagh@pit.uni-tuebingen.de 相似文献
5.
Yi-Chen Yeh Chun-Han Chiu Juh Tzeng Lue 《Applied Physics A: Materials Science & Processing》2009,94(4):923-926
We have observed an abnormal electron transport characteristic from the Ni–Mn–Ni triple-layered magnetic thin-films. Due to
the intercalated Mn ultra-thin interlayer, the magnetic domain structure and the electron transport characteristic differ
a lot from their original magnetic (Fe, Co, and Ni) films. As inspected by a magnetic force microscopy (MFM), we observed
the variation of the domain configuration with Mn interlayer thicknesses (for 1, 5, and 10 nm). Moreover, we also examined
and found that the direct current (DC) resistivity have no significant change as the current conducts from the current-in-wall
(CIW) to the current- perpendicular-to-wall (CPW), which are opposite to the results of single layered films. 相似文献
6.
Pressure effects on magnetic properties and martensitic transformation of Ni–Mn–Sn magnetic shape memory alloys
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The mechanism for the effects of pressure on the magnetic properties and the martensitic transformation of Ni-Mn- Sn shape memory alloys is revealed by first-principles calculations. It is found that the total energy difference between paramagnetic and ferromagnetic austenite states plays an important role in the magnetic transition of Ni-Mn-Sn under pressure. The pressure increases the relative stability of the martensite with respect to the anstenite, leading to an increase of the martensitic transformation temperature. Moreover, the effects of pressure on the magnetic properties and the martensitic transformation are discussed based on the electronic structure. 相似文献
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Fe–Pt–MgO stacked storage layer constructed by [Fe–Pt/Fe–Pt–MgO/Fe–Pt] trilayered structure was proposed for a next-generation high-density perpendicular magnetic recording medium. The Fe–Pt–MgO composite middle layer was prepared by sputtering the Fe–Pt–MgO composite-type target including relatively large MgO content of 50 vol%. The Fe–Pt(0 0 1) seed layer deposited on MgO underlayer was effective in forming the ordered fct(0 0 1) phase for the Fe–Pt–MgO composite film. The reduction of transition jitter noise and the suppression of signal overlap were observed in the stacked-type medium with the Fe–Pt–MgO middle layer of 1 nm thickness. The improvement of recording properties is attributed to the pinning effect of magnetic domain wall by the Fe–Pt–MgO composite layer inserted into the middle of pure Fe–Pt storage layer. 相似文献
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《Journal of magnetism and magnetic materials》2001,232(3):189-193
A microstructural study of DC-sputtered Fe93−xZr3B4Agx films on Si(0 0 1) substrates has been carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). All samples were deposited as a function of additive Ag content (x=0–6 at%), and annealed in the range of temperature, 300–600°C, for 1 h in order to obtain enhanced soft magnetic properties. Through XRD and TEM investigation, Ag-free Fe93Zr3B4 films on Si(0 0 1) substrates consisted of nano-crystalline Fe-based phases. In the presence of Ag additive element, the microstructure of as-deposited Fe93−xZr3B4Agx films consisted of a mixture of majority of Fe-based amorphous and Ag crystalline phases. In this case, additive element, Ag played a role in retarding the formation of Fe-based crystalline phases during deposition, and insoluble nano-crystalline Ag particles were dispersed in the Fe-based amorphous matrix. As the content of Ag increased, the intensity of Ag crystalline XRD peak increased. Crystallization of Fe-based amorphous phase in the matrix of Fe88Zr3B4Ag5 thin films occurred at an annealing temperature of 400°C. In the case of Fe88Zr3B4Ag5 films annealed at 500°C, a much enhanced permeability of the Fe-based alloy thin films associated with nano-crystalline phases was achieved. 相似文献
10.
V. V. Korovushkin V. G. Kostishin M. A. Stepovich M. N. Shipko 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(12):1450-1454
The effect weak (10–100 kA m–1) low-frequency (10–20 Hz) pulsed magnetic fields have on the surface structure and magnetic characteristics of yttrium–iron garnet Y3Fe5O12 is studied by means of electron and Mössbauer spectroscopy. A mechanism is proposed for the variation of saturation magnetization in Y3Fe5O12 after magnetic pulse treatment. The mechanism is associated with the change in the spin state of iron ions localized in the tetrahedral sublattice. 相似文献
11.
《Superlattices and Microstructures》1998,24(1):93-97
A magnetic memory effect is observed in the absorption of electromagnetic waves of 20–70 MHz in YBa2Cu3O7at 77–300 K. 相似文献
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Abdul Majid Rehana Sharif J. J. Zhu Akbar Ali 《Applied Physics A: Materials Science & Processing》2009,96(4):979-984
Mn ions have been incorporated into MOCVD grown Al1−x
In
x
N/GaN thin films by ion implantation to achieve the room temperature ferromagnetism in the samples. Magnetic characterizations
revealed the presence of two ferromagnetic transitions: one has Curie points at ∼260 K and the other above room temperature.
In-diffusion of indium caused by the Mn implantation leads to the partition of AlInN epilayer into two diluted magnetic semiconductor
sub-layers depending on the Mn concentration. The Curie temperature of 260 K is assigned to the layer having lower concentration,
whereas T
c
above room temperature is assumed to be associated to the layer having higher Mn concentration. 相似文献
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A.C.F.M. Costa A.P.A. Diniz A.G.B. de Melo R.H.G.A. Kiminami D.R. Cornejo A.A. Costa L. Gama 《Journal of magnetism and magnetic materials》2008
Ni–Zn ferrites have been widely used in components for high-frequency range applications due to their high electrical resistivity, mechanical strength and chemical stability. Ni–Zn ferrite nanopowders doped with samarium with a nominal composition of Ni0.5Zn0.5Fe2−xSmxO4 (x=0.0, 0.05, and 0.1 mol) were obtained by combustion synthesis using nitrates and urea as fuel. The morphological aspects of Ni–Zn–Sm ferrite nanopowders were investigated by X-ray diffraction, nitrogen adsorption by BET, sedimentation, scanning electron microscopy and magnetic properties. The results indicated that the Ni–Zn–Sm ferrite nanopowders were composed of soft agglomerates of nanoparticles with a high surface area (55.8–64.8 m2/g), smaller particles (18–20 nm) and nanocrystallite size particles. The addition of samarium resulted in a reduction of all the magnetic parameters evaluated, namely saturation magnetization (24–40 emu/g), remanent magnetization (2.2–3.5 emu/g) and coercive force (99.3–83.3 Oe). 相似文献
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《Photonics and Nanostructures》2014,12(5):473-481
Electrodynamic properties of the graphene–magnetic semiconductor–graphene sandwich-structure have been investigated theoretically with taking into account the dissipation processes. Influence of graphene layers on electromagnetic waves propagation in graphene–semi-infinte magnetic semiconductor and graphene–magnetic semiconductor–graphene sandwich-structure has been analyzed. Frequency and field dependences of the reflectance, transmittance and absorbtance of electromagnetic waves by such structure have been calculated. The size effects associated with the thickness of the structure have been analyzed. The possibility of efficient control of electrodynamic properties of graphene–magnetic semiconductor–graphene sandwich-structure by an external magnetic field has been shown. 相似文献
17.
L.S. Vaidhyanathan M.P. Janawadkar 《Physica C: Superconductivity and its Applications》2010,470(17-18):693-695
Resistance oscillations as a function of magnetic field were observed in superconductor–magnetic tunnel junctions of Nb–Fe–FeOx–SiO2–Au–Nb. Junctions involving superconductor–magnetic layer superconductor system are exciting because for certain regime of ferromagnetic layer thickness, a Josephson coupling with an intrinsic phase difference of π might be stabilized. For fabrication of the tunnel junctions the thin films were deposited by RF/DC magnetron sputtering. Using photolithography and reactive ion etching, square junctions of size varying from 50 μm to 250 μm were defined. I–V characteristics and R vs. H characteristics were studied at 4.2 K. When the magnetic field is applied parallel to the junction plane, measurements of the junction resistance as a function of magnetic field at a fixed temperature show resistance peaks whenever the total magnetic flux through the junction equals an integral multiple of flux quantum. The penetration depth of the superconducting electrodes was estimated from the positions of the resistance peaks. 相似文献
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Leonardo Campanelli 《Chinese Journal of Physics (Taipei)》2018,56(1):91-95
We study the generation of cosmic magnetic fields during de Sitter inflation in a non-conformally-invariant effective model of massive electrodynamics containing a four-photon interaction term. We show that, if the photon self-coupling is strong enough, comoving magnetic fields correlated on scales of 10kpc and of intensities are produced as excitation of the vacuum. If amplified by galactic dynamo, they naturally explain the existence of galactic magnetic fields. 相似文献
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