共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Gerbaldo G. Ghigo G. Giunchi L. Gozzelino F. Laviano E. Mezzetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):297-300
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the
material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis.
A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous
polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous
part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration,
at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic
granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a
network of strongly coupled Josephson junctions.
Received 31 May 2001 and Received in final form 5 December 2001 相似文献
2.
Sun Guoya Xing D.Y. Shen R. Lin H.Q. 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):33-38
The Nambu spinor Green's function approach is applied to calculating the density of states (DOS) and superconducting order
parameter in normal-metal/insulator/ferromagnet/superconductor (NM/I/FM/SC) junctions. It is found that the s-wave superconductivity and ferromagnetism can coexist near the FM/SC interface, which is induced by proximity effect. On
the SC side, the spin-dependent DOS appears both within and without the energy gap. On the FM side, the superconducting order
parameter displays a damped oscillation and the DOS exhibits some superconducting behavior. The calculated result for the
DOS in FM for “0 state” and “π state” can reproduce recent tunneling spectra in Al/Al2O3/PdNi/Nb tunnel junctions.
Received 1st July 2002 Published online 19 November 2002 相似文献
3.
Y. Guo B. Wang B.-L. Gu Y. Kawazoe 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):509-513
We investigate characteristics of spin tunneling time in ZnSe/Ze1-xMnxSe multilayers under the influence of both an electric field and a magnetic field. The results indicate that the tunneling
time shows complicated oscillations and significant spin separation for electrons with different spin orientations traversing
semimagnetic semiconductor heterostructures. It is also shown that the tunneling time exhibits obvious asymmetry in opposite
tunneling directions for electrons tunneling through asymmetric heterostructures, which mainly occurs in resonant regions.
The degree of the asymmetry of the tunneling time is not only spin-polarization dependent but also external-field induced.
Received 10 July 2001 相似文献
4.
V. Apinyan R. Mélin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):373-389
We consider a microscopic theory of F/S/F trilayers with metallic or insulating ferromagnets. The trilayer with metallic ferromagnets
is controlled by the formation of non local pair correlations among the two ferromagnets which do not exist with insulating
ferromagnets. The difference between the insulating and ferromagnetic models can be understood from lowest order diagrams.
Metallic ferromagnets are controlled by non local pair correlations and the superconducting gap is larger if the ferromagnetic
electrodes have a parallel spin orientation. Insulating ferromagnets are controlled by pair breaking and the superconducting
gap is smaller if the ferromagnetic electrodes have a parallel spin orientation. The same behavior is found in the presence
of disorder in the microscopic phase variables and also in the presence of a partial spin polarization of the ferromagnets.
The different behaviors of the metallic and insulating trilayers may be probed in experiments.
Received 4 July 2001 and Received in final form 8 November 2001 相似文献
5.
Z.Y. Zeng Baowen Li F. Claro 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):401-405
A unified theory for the current through a mesoscopic region of interacting electrons connected to two leads which can be
either ferromagnet or superconductor is presented, yielding Meir-Wingreen-type formulas when applied to specific circumstances.
In such a formulation, the requirement of gauge invariance is satisfied automatically. Moreover, one can judge unambiguously
what quantities can be measured in the transport experiment.
Received 22 August 2002 / Received in final form 14 February 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: phyzengz@nus.edu.sg 相似文献
6.
Josephson current is investigated in the superconductor/ferromagnet/superconductor junction. It was shown that the current exhibited damping oscillations as a function of the ferromagnetic layer thickness. Previous theories based on Usadel or Eilenberger equations have predicted that the damping length and oscillation period divided by 2π were the same for weak ferromagnetic spacer. This contradicts past experiments. A new calculation of the Josephson current is proposed. The Gorkov equations are solved taking into account s–d scattering in ferromagnet. It is shown that the oscillation period depends only on the exchange magnetic field in the spacer, whereas the damping length is connected to the ferromagnetic mean free path. The concordance with the former experiment allows one to conclude that s–d scattering as a pair-breaking mechanism plays a significant role in the proximity effect in S/F heterostructures. 相似文献
7.
J.-P. Wang H. Meng 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):471-474
Spin torque transfer structures with new spin switching configurations are
proposed, fabricated and investigated in this paper. The non-uniform
current-induced magnetization switching is implemented based on both GMR and
MTJ nano devices. The proposed new spin transfer structure has a hybrid free
layer that consists of a layer with conductive channels (magnetic) and
non-conductive matrix (non-magnetic) and traditional free layer(s). Two
mechanisms, a higher local current density by nano-current-channels and a
non-uniform magnetization switching (reversal domain nucleation and growth)
by a magnetic nanocomposite structure, contribute in reducing the switching
current density. The critical switching current density for the new spin
transfer structure is reduced to one third of the typical value for the
normal structure. It can be expected to have one order of magnitude or more
reduction for the critical current density if the optimization of materials
and fabrication processes could be done further. Meanwhile, the thermal
stability of this new spin transfer structure is not degraded, which may
solve the long-standing scaling problem for magnetic random access memory
(MRAM). This spin transfer structure, with the proposed and demonstrated new
spin switching configurations, not only provides a solid approach for the
practical application of spin transfer devices but also forms a unique
platform for researchers to explore the non-uniform current-induced
switching process. 相似文献
8.
N.N. Garif'yanov Y.V. Goryunov T. Mühge L. Lazar G.G. Khaliullin K. Westerholt I.A. Garifullin H. Zabel 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):405-407
We have studied superconducting and magnetic properties of sputtered Fe/Pb/Fe-trilayers. For a fixed Pb thickness and with changing Fe thickness, , a monotonic decrease of the superconducting transition temperature was observed. Magnetization measurements clearly showed that Fe remains ferromagnetic down to the monolayer range. A quantitative
comparison of with the theory of pair breaking by the exchange field reveals that the observed -suppression by the ferromagnetic Fe-layer is much weaker than expected. Possible reasons for the reduced -suppression in this system are discussed.
Received: 30 June 1997 / Revised: 20 August 1997 / Accepted: 16 December 1997 相似文献
9.
M. Giroud K. Hasselbach H. Courtois D. Mailly B. Pannetier 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):103-109
We present electrical transport experiments performed on submicron hybrid devices made of a ferromagnetic conductor (Co) and
a superconducting (Al) electrode. The sample was patterned in order to separate the contributions of the Co conductor and
of the Co-Al interface. We observed a strong influence of the Al electrode superconductivity on the resistance of the Co conductor.
This effect is large only when the interface is highly transparent. We characterized the dependence of the observed resistance
decrease on temperature, bias current and magnetic field. As the differential resistance of the ferromagnet exhibits a non-trivial
asymmetry, we claim that the magnetic domain structure plays an important role in the electron transport properties of superconducting
/ ferromagnetic conductors.
Received 9 July 2002 / Received in final form 22 October 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: herve.courtois@grenoble.cnrs.fr
RID="b"
ID="b"associated to Université Joseph Fourier 相似文献
10.
A. Saffarzadeh 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):149-153
Spin-polarized tunneling in FMS/M/FMS double tunnel junctions where FMSs are ferromagnetic semiconductor layers and M is a
metal spacer is studied theoretically within the single-site coherent potential approximation (CPA). The exchange interaction
between a conduction electron and localized moment of the magnetic ion is treated in the framework of the s-f model. The spin polarization in the FMS layers is observed to oscillates as a function of the number of atomic planes in
the spacer layer. Amplitude of these oscillations decreases with increasing the exchange interaction in FMS layers.
Received 9 June 2001 and Received in final form 20 August 2001 相似文献
11.
E.I. Rashba 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(4):513-527
Insertion of a resistive contact between a ferromagnetic metal and a semiconductor microstructure is of critical importance
for achieving efficient spin injection into a semiconductor. However, the equations of the diffusion theory are rather cumbersome
for the junctions including such contacts. A technique based on deriving a system of self-consistent equations for the coefficients
of spin injection, γ, through different contacts are developed. These equations are concise when written in the proper notations.
Moreover, the resistance of a two-contact junction can be expressed in terms of γ's of both contacts. This equation makes
calculating the spin valve effect straightforward, allows to find an explicit expression for the junction resistance and to
prove that its nonequilibrium part is positive. Relation of these parameters to different phenomena like spin-e.m.f. and the
contact transients is established. Comparative effect of the Coulomb screening on different parameters is clarified. It is
also shown that the spin non-conservation in a contact can have a dramatic effect on the non-equilibrium resistance of the
junction.
Received 2 May 2002 / Received in final form 26 July 2002 Published online 15 October 2002
RID="a"
ID="a"Also at the Department of Physics, MIT, Cambridge, Massachusetts 02139, USA e-mail: erashba@mailaps.org 相似文献
12.
H. Pan S.-Q. Duan L.-N. Zhao W.-D. Chu W. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(1):71-76
We theoretically study the spin pump effects of the rotating
magnetic field on the spin current through two coupled quantum dots.
Owing to the interdot coupling, two molecular states with different
bands can be formed, resulting asymmetric spin current peaks. The
possibility of manipulating the spin current is explored by tuning
the strength, the frequency, and the direction of the rotating
magnetic field. The number and location of the spin current peaks
can be controlled by making use of various tunings. Furthermore, the
normal 2π period of the spin current with respect to the
magnetic flux can be destroyed by the interdot coupling. 相似文献
13.
Employing mutual-inductance measurements, we study the magnetic field dependence of complex AC susceptibility of artificially prepared highly ordered (periodic) two-dimensional Josephson junction arrays of unshunted Nb-AlOx-Nb junctions. The observed behavior can be explained assuming single-plaquette approximation of the overdamped model with an inhomogeneous critical current distribution within a single junction. 相似文献
14.
R. Migliore A. Messina A. Napoli 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(1):111-115
A simple way to acquire information on the mean values of the phase operators sinϕ and cosϕ of an ultrasmall Josephson junction
prepared in an arbitrary pure or not state is reported. Our proposal exploits the recently predicted occurrence of current
spikes in the I-V characteristic of a mesojunction irradiated by a quantum single-mode low-intensity coherent electromagnetic field. A necessary
condition for the validity of our treatment is presented and discussed.
Received 11 April 2001 相似文献
15.
R.L. Leheny Y.S. Lee G. Shirane R.J. Birgeneau 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):287-290
Inelastic neutron scattering with high wave-vector resolution has characterized the propagation of transverse spin wave modes
near the antiferromagnetic zone center in the metastable domain state of a random field Ising magnet. A well-defined, long
wavelength excitation is observed despite the absence of long-range magnetic order. Direct comparisons with the spin wave
dispersion in the long-range ordered antiferromagnetic state reveal no measurable effects from the domain structure. This
result recalls analogous behavior in thermally disordered anisotropic spin chains but contrasts sharply with that of the phonon
modes in relaxor ferroelectrics.
Received 2 November 2002 / Received in final form 4 February 2003 Published online 11 April 2003
RID="a"
ID="a"leheny@pha.jhu.edu 相似文献
16.
F. Liang Y. H. Yang J. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):337-341
We propose an electrical scheme for the generation of a pure spin current without a charge current in a two-terminal device,
which
consists of a scattering region of a two-dimensional electron gas
(2DEG) with Rashba (R) and/or Dresselhaus (S) spin-orbit interaction (SOI)
and two normal leads. The SOI is modulated by a time-dependent gate
voltage to pump a spin current. Based on a tight-binding model and
the Keldysh Green’s function technique, we obtain the analytical
expression of the spin current. It is shown that a pure spin current
can be pumped out, and its magnitude could be modulated by
device parameters such as the oscillating frequency of the SOI, as
well as the SOI strength. Moreover, the spin polarisation direction of
the spin current could also be tuned by the strength ratio between
RSOI and DSOI. Our proposal provides not only a fully electrical means
to generate a pure spin current but also a way to control the spin
polarisation direction of the generated spin current. 相似文献
17.
G. Hammerl H. Bielefeldt S. Leitenmeier A. Schmehl C.W. Schneider A. Weber J. Mannhart 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):299-301
For many applications of polycrystalline high-T
c superconductors the small critical currents of the grain boundaries pose a severe problem. To solve this problem, we derive
novel designs for the microstructure of coated conductors.
Received 25 February 2002 Published online 6 June 2002 相似文献
18.
Z. P. Niu Z. M. Zheng D. Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):281-287
Four-component Bogoliubov-de Gennes equations are applied to study
tunneling conductance spectra of ferromagnet/ferromagnet/d-wave
superconductor (F1/F2/d-wave S) tunnel junctions and to find
out signs of spin-triplet pairing correlations induced in the
proximity structure. The pairing correlations with equal spins
arises from the novel Andreev reflection (AR), which requires at
least three factors: the usual AR at the F2/S interface, spin
flip in the F2 layer, and superconducting coherence kept up in
the F2 layer. Effects of angle α between magnetizations of
the two F layers, polarizations of the F1 and F2 layers, the
thickness of the F2 layer, and the orientation of the d-wave S crystal on the tunneling conductance are investigated. A conversion
from a zero-bias conductance dip at α = 0 to a zero-bias
conductance peak at a certain value of α can be seen as a
sign of generated spin-triplet correlations. 相似文献
19.
K. P. McKenna G. J. Morgan 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):451-456
A quantum equation of motion method is applied to simulate conduction electron spin-relaxation and transport in the presence
of the spin-orbit interaction and disorder. A spin-relaxation time of 25ps is calculated for Cu with a realistic low temperature
resistivity of 3.2 μΩ cm – corresponding to a spin-diffusion length of about 0.4 μm. Spin-relaxation in a finite nanocrystallite
of Cu is also simulated and a short spin-relaxation time (0.47 ps) is calculated for a crystallite with 7% surface atoms.
The spin-relaxation calculated for bulk Cu is in good agreement with experimental evidence, and the dramatic nanocrystallite
effect observed has important implications for nano-spintronic devices. 相似文献
20.
G.B. Lesovik T. Martin G. Blatter 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):287-290
A weakly biased normal-metal-superconductor junction is considered as a potential device injecting entangled pairs of quasi-particles
into a normal-metal lead. The two-particle states arise from Cooper pairs decaying into the normal lead and are characterized
by entangled spin- and orbital degrees of freedom. The separation of the entangled quasi-particles is achieved with a fork
geometry and normal leads containing spin- or energy-selective filters. This solid state entangler is characterized by noise
cross-correlations which are identical to the noise in one lead, a signature consistent with entanglement. A connection to
Bell-type experiments is envisioned (cond-mat/0009193).
Received 20 September 2001 相似文献