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1.
S. Bellucci P. Onorato 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):35-40
We propose a new scheme of spin filtering employing ballistic
nanojunctions patterned in a two dimensional electron gas
(2DEG). Our proposal is essentially based on the spin-orbit (SO)
interaction generated by a lateral confining potential (β-SO
coupling ).
We demonstrate that the flow of a longitudinal unpolarized current
through a ballistic T and X junction with this spin-orbit
coupling will induce a spin accumulation which has opposite signs
for the two lateral probes and is, therefore, the principal
observable signature of the spin Hall effect in these devices. 相似文献
2.
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
3.
A. Phirouznia M. M. Tehranchi M. Ghanaatshoar 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):103-107
For an ideal one-dimensional ferromagnetic wire with a
magnetic domain wall (DW), contribution of the DW to the resistivity of the
system has been investigated. We have studied the resistance due to the
magnetic impurities in the domain wall which was suspended in a weak
magnetic field for two types of chiralities. The analysis has been based on
Boltzmann transport equation, within the relaxation time approximation.
Through this formalism, both increasing and decreasing of the resistance due
to the DW have been predicted in presence of Zeeman interaction as an
extrinsic mechanism. 相似文献
4.
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
5.
S. Bellucci F. Carillo P. Onorato 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(4):509-515
We suggest a spin filter scheme using T-stub nanometric
crossjunctions patterned in two dimensional electron gases (2DEGs)
in the presence of spin orbit interaction (SOI).
We compare the effects of SOI arising from vertical confinement of charge carriers
in the well, Rashba or α-SOI, with SOI generated by lateral
confinement of the wire, β-SOI. We show that β coupling
can be more effective in generating a spin polarized current as
compared to α-SOI. We also compare the efficiency of the
T-stub filter with the one of the X shaped cross junction. 相似文献
6.
M. Ziese R. Höhne H.C. Semmelhack H. Reckentin N.H. Hong P. Esquinazi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):415-422
The magnetotransport properties of magnetite films with different microstructures were investigated in order to identify prerequisites
for the attainment of a large tunnelling magnetoresistance in polycrystalline samples. Epitaxial films on MgAl2O4, polycrystalline films on Al2O3 and rough MgAl2O4 substrates and a polycrystalline La0.7Ca0.3MnO3 film on MgO were compared. Although grain boundaries induce a large high-field magnetoresistance in magnetite films, the
low-field magnetoresistance characteristic for spin-polarized tunnelling was virtually absent in these samples. Two factors
might be responsible for this behaviour: (1) grain boundaries in magnetite are conducting and do not form tunnelling barriers
and (2) the spin-polarization near grain boundaries is suppressed due to non-stoichiometry.
Received 15 April 2002 Published online 13 August 2002 相似文献
7.
C. Stockinger W. Markowitsch W. Lang W. Kula R. Sobolewski 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):301-311
We report our studies on the superconducting and normal-state properties of metallic thin films ( 52 K) exposed to long-term white-light illumination (photodoping). It was observed that the effects of photoexcitation strongly
depended on the temperature at which the photodoping was performed. At low temperatures, both the Hall mobility and the Hall
number were photoenhanced, whereas, at temperatures slightly below room temperature, the Hall mobility initially showed an
abrupt increase followed by a long-term decrease, and the Hall number increased even stronger than at low temperatures. The
enhancement of the film's superconducting transition temperature Tc, caused by photodoping, exhibited the same temperature dependence as the enhancement of the Hall number, being largest ( 2.6 K) at high temperatures. From the asynchronous behavior of the Hall quantities, we conclude that both the photoassisted
oxygen ordering and charge transfer mechanisms contribute to photodoping. The relative contributions of both mechanisms and,
thus, the electronic properties of the photoexcited state are strongly temperature dependent. Studies of the relaxation of
the photoexcited state at 290 K showed an unexpectedly short relaxation time of the Hall mobility after termination of the
illumination. The relaxation saturated somewhat below the initial, undoped value, similarly to the decrease of the Hall mobility,
observed upon long illumination. These latter findings give evidence for a competition between the oxygen ordering and thermal
disordering processes during and after the photoexcitation in the high-temperature range.
Received: 13 October 1997 / Accepted: 19 November 1997 相似文献
8.
Y. Saito T. Inokuchi H. Sugiyama K. Inomata 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):463-469
We conducted a detailed study of hard axis magnetic field (Hhard)
dependence on current-induced magnetization switching (CIMS) in MgO-based
magnetic tunnel junctions (MTJs) with various junction sizes and various
uniaxial anisotropy fields. The decreases in critical current density
(Jc) and the intrinsic critical current density (Jc0) estimated from
the pulse duration dependence on Jc in CIMS are observed when applying
Hhard for all MTJs. The decrease in energy barrier of CIMS is also
observed except for the largest sample. These results indicate that the
reduction of Jc is attributable to both the increase of spin-transfer
efficiency and the decrease in energy barrier in the case of applying
Hhard. The Jc0 decreases with increase in the mutual angle between
the direction of magnetization and the easy axis (θf),
which is consistent with the theoretical prediction proposed by Slonczewski.
The degree of the reduction of Jc0 for the same value of Hhard
decreases with decreasing size of MTJs. This behavior is considered to be
related to not only decrease in θf due to the increase in
anisotropy field in MTJs, but also to the increase in the variance of the
initial angle of magnetization due to the thermally activated magnon
excitation. The stable switching endurance related to CIMS was observed in a
wide range of MTJ sizes when applying Hhard. Moreover, we proposed a new
architecture and a new switching method considering write disturbance. These
results would be useful for application to spin memory and other
spin-electronic devices. 相似文献
9.
P. Schwab R. Raimondi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):483-495
We show that in the metallic phase of a two dimensional electron gas the spin-orbit coupling due to structure inversion asymmetry
leads to a characteristic anisotropy in the magnetoconductance. Within the assumption that the metallic phase can be described
by a Fermi liquid, we compute the conductivity in the presence of an in-plane magnetic field. Both the spin-orbit coupling
and the Zeeman coupling with the magnetic field give rise to two spin subbands, in terms of which most of the transport properties
can be discussed. The strongest conductivity anisotropy occurs for Zeeman energies of the order of the Fermi energy corresponding
to the depopulation of the upper spin subband. The energy scale associated with the spin-orbit coupling controls the strength
of the effect. More in particular, we find that the detailed behavior and the sign of the anisotropy depends on the underlying
scattering mechanism. Assuming small angle scattering to be the dominant scattering mechanism our results agree with recent
measurement on Si-MOSFET's in the vicinity of the metal-insulator transition.
Received 11 July 2001 相似文献
10.
W. Westerburg F. Martin P.J.M. van Bentum J.A.A.J. Perenboom G. Jakob 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):509-513
We measured the temperature dependence of the linear high field Hall resistivity of ( K) and ( K) thin films in the temperature range from 4 K up to 360 K in magnetic fields up to 20 T. At low temperatures we find a
charge-carrier density of 1.3 and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In this temperature
range electron-magnon scattering contributes to the longitudinal resistivity. At the ferromagnetic transition temperature
a dramatic drop in the number of charge-carriers n down to 0.6 holes per unit cell, accompanied by an increase in unit cell volume, is observed. Corrections of the Hall data
due to a non saturated magnetic state will lead a more pronounced charge-carrier density collapse.
Received 22 July 1999 and Received in final form 7 October 1999 相似文献
11.
12.
N.A. Babushkina L.M. Belova E.A. Chistotina O.Yu. Gorbenko A.R. Kaul B. Güttler K.I. Kugel 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):409-415
The effect of
16
O
→
18
O isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La0.35Pr0.35Ca0.3MnO3 epitaxial thin films deposited onto LaAlO3 and SrTiO3 substrates. For the films on LaAlO3, the isotope substitution resulted in the reversible transition from a metal-like to insulating state. The applied magnetic
field ( H
≥ 2
T) transformed the sample with 18O back to the metallic state. The films on SrTiO3 remained metallic at low temperatures for both 16O and 18O, but the shift of the resistivity peak corresponding to onset of metallic state exceeded 63 K after
16
O
→
18
O substitution. The temperature dependence of both resistivity and magnetic susceptibility was characterized by hysteresis,
especially pronounced in the case of the films on LaAlO3. Such a behavior gives certain indications of the phase separation characteristic of interplay between ferromagnetism and
charge ordering.
Received 11 February 2000 and Received in final form 13 September 2000 相似文献
13.
P. Schwab R. Raimondi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):5-8
We consider non-equilibrium transport in disordered conductors. We calculate the interaction correction to the current for
a short wire connected to electron reservoirs by resistive interfaces. In the absence of charging effects we find a universal
current-voltage-characteristics. The relevance of our calculation for existing experiments is discussed as well as the connection
with alternative theoretical approaches.
Received 2 September 2002 Published online 29 October 2002 相似文献
14.
A. N. Useinov L. R. Tagirov R. G. Deminov Y. Zhou G. Pan 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):187-192
We investigated the mean-free path effects
on the magnetoresistance of ferromagnetic nanocontacts.
For most combinations of parameters the magnetoresistance
monotonously decreases with increasing the contact cross-section.
However, for a certain choice of parameters the calculations show
non-monotonous behavior of the magnetoresistance
in the region in which the diameter of the contact becomes
comparable with the mean-free path of electrons.
We attribute this effect to different conduction
regimes in the vicinity of the nanocontact: ballistic for electrons of
one spin projection, and simultaneously diffusive for the other.
Furthermore, at certain combinations of spin asymmetries
of the bulk mean-free paths in a heterocontact, the
magnetoresistance can be almost constant,
or may even grow as the contact diameter increases.
Thus, our calculations suggest a way to search
for combinations of material parameters,
for which high magnetoresistances can be achieved
not only at the nanometric size of the contact, but also at much
larger cross-sections of nanocontacts which can be
easier for fabriaction with current technologies.
The trial calculations of the magnetoresistance with material parameters
close to those for the Mumetal-Ni heterocontacts agree satisfactorily
with the available experimental data. 相似文献
15.
F.B. Anders M. Huth 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):491-499
We present calculations of the electronic transport properties of heavy-fermion systems within a semi-phenomenological approach
to the dynamical mean field theory. In this approach the dynamics of the Hund's rules 4f (5f )-ionic multiplet split in a crystalline environment is taken into account. Within the scope of this calculation we use the
linear response theory to reproduce qualitative features of the temperature-dependent resistivity and hall conductivity, the
magneto-resistivity and the thermoelectric power typical for heavy-fermion systems. The model calculations are directly compared
with experimental results on CeCu
2
Si
2.
Received 30 June 2000 and Received in final form 15 December 2000 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.
C. Stockinger G. Heine W. Markowitsch W. Lang R. Adam R. Sobolewski R. Rössler J.D. Pedarnig D. Bäuerle 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):227-231
() thin films were photodoped with white light at various temperatures from 70 K to 290 K. Before and after the excitation,
the magnetoconductivity was measured in a magnetic field B
= 0.5 T, and the experimental results were fitted to the Aslamazov-Larkin theory of superconducting order-parameter fluctuations
to determine the superconducting coherence lengths, and . We observed that the photodoping process enhanced and and that the amount increased with the photodoping temperature increase. On the other hand, the superconducting anisotropy
/ decreased with increasing temperature. The photodoping effect enhances superconducting properties of partially oxygen-deficient
samples and is considerably increased by high doping temperatures.
Received 15 December 1999 and Received in final form 24 May 2000 相似文献
18.
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
19.
G. Bergmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):19-25
A new method is suggested to investigate the mechanism of the anomalous Hall
effect (AHE) in ferromagnetic metals. Using a double layer of a ferromagnet
and a normal metal of increasing thickness one can manipulate the AHE in the
ferromagnet without changing the ferromagnet's structure and electronic
properties. The conduction electrons from the normal metal carry their drift
velocity across the interface into the ferromagnetic film and induce an
additional AHE conductance ΔGxy. Its dependence on the mean free
path in the normal metal distinguishes between the side jump and the skew
scattering mechanisms for the AHE in the ferromagnet. 相似文献
20.
A. Cresti G. Grosso G. Pastori Parravicini 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(4):537-549
This paper addresses in a concise and rigorous way the basic tools for the study of local longitudinal and transverse microscopic
currents in two-dimensional devices. The emphasis is on the optimized use of the Keldysh nonequilibrium Green's function theory
together with the tight-binding representation of the electronic system. We elaborate general analytic expressions of current
profiles, useful for modeling and simulating the local site-to-site flow of carriers; furthermore, in broken time-reversal
symmetry, the formalism discerns unambiguously persistent and transport contributions to the bond currents. Our approach achieves
a workable theoretical imaging, resolved in space and energy, of the microscopic currents through mesoscopic devices. 相似文献