Spin Dependent Transport Properties

The left part of Fig. 5.2 shows the attenuation of the photoemission signal from tungsten versus film thickness filled diamond denote the intensity in the spin 

It seems to be possible to explain the polarization enhancement of secondary electrons by the spin dependence of the IMFP. This means, the different attenuation lengths act as a spin filter, majority electrons preferentially allowing to be transmitted. The spin asymmetry of the IMFP, given by A = (2+ — 2 )/(2+ + 2 ), amounts to about 20% for both systems and is confirmed by an investigation of Fe/Cu(100) [8] leading to the same value of A. A very effective spin filter can be realized by a graphene layer which was theoretically predicted [11] and experimentally verified for graphene on Ni(lll) [12]. 

---

In the first part of this chapter it will be reported on spin dependent transport and surface magnetic properties of itinerant magnetic substrates, thin Fe(l 10) and Co(OOOl) films evaporated on W(110), which were investigated by these electron emission techniques. Subsequently, the behavior of adsorbates will be discussed from the point of view whether they change the properties of the surface and whether they feel the magnetism of the underlying substrate. This discussion will be carried out for the example of oxygen which adsorbs dissociatively on the above mentioned surfaces. 

The above qualitative picture is supported by the data of frequency-dependent transport properties. The frequency dependence of conductivity provides another, independent way of determining the effective dimensionality d. In disordered systems the conductivity as a function of frequency usually follows a power law o- o>. Considering that the basic process of conduction is an anomalous diffusion, i.e., a random walk of the charge carriers on a network of effective dimensionality d < d, where d is the space dimension ( = 3 in the present case), the exponent s can be expressed as = 1 - did. This expression with data of conductivity versus frequency given in the literature [106] leads to values for d that agree satisfactorily with those obtained from spin dynamics. 

Perovskite materials have many interesting and spectacular properties such as high temperature superconductors, magneto resistance, ferroelectricity, charge ordering, spin dependent transport, high thermo power, optical properties, etc. As well as their applications in catalyst electrodes in certain types of fuel cells, memory devices, etc. 

Perovskite materials (ABX3) exhibit many fascinating properties from both theoretical and application perspectives, including ferroelectricity, superconductivity, charge ordering, and spin-dependent transport. The interplay of compositional, structural, optical, and transportation properties is commonly observed in this family, making them promising candidates as photocatalysts. Perovskites are characterised by a crystal structure similar to that of calcium titanium oxide (CaTiOs). Normally A and B sites are occupied by two cations with very different sizes (dA > dfi), whereas X (normally O) is an anion that bonds to both. In the ideal cubic-symmetry structure, the A and B cations are 12- and sixfold coordinated in bulk and surrounded by cuboctahedron and octahedron of anions, respectively. 

Many ferromagnets are metals or metallic alloys with delocalized bands and require specialized models that explain the spontaneous magnetization below Tc or the paramagnetic susceptibility for T > Tc. The Stoner-Wohlfarth model,6 for example, explains these observed magnetic parameters of d metals as by a formation of excess spin density as a function of energy reduction due to electron spin correlation and dependent on the density of states at the Fermi level. However, a unified model that combines explanations for both electron spin correlations and electron transport properties as predicted by band theory is still lacking today. 

Spin-orbit(SO) coupling is an important mechanism that influences the electron spin state [1], In low-dimensional structures Rashba SO interaction comes into play by introducing a potential to destroy the symmetry of space inversion in an arbitrary spatial direction [2-6], Then, based on the properties of Rashba effect, one can realize the controlling and manipulation of the spin in mesoscopic systems by external fields. Recently, Rashba interaction has been applied to some QD systems [6-8]. With the application of Rashba SO coupling to multi-QD structures, some interesting spin-dependent electron transport phenomena arise [7]. In this work, we study the electron transport properties in a three-terminal Aharonov-Bohm (AB) interferometer where the Rashba interaction is taken into account locally to a QD. It is found that Rashba interaction changes the quantum interference in a substantial way. 

The methodological background to obtaining the transport properties from discrete compartments is the formalism used by Cory and Garroway (50) to obtain the displacement profile (15) of molecules in a dispersed system. Detailed information on the mole cular motion may be obtained by measuring the A dependence of the apparent diffusion coefficient caused by a possible obstruction of the spin motion. The stimulated echo sequence, Fig. 9a, is usually used to probe various diffusion times, A. As is seen from the fig-... 

Depending on the magnetic ground state of the ytterbimn atoms we observe a variety of diflerent transport properties. Several of the YhTX intermetallics behave like classical metals. In those cases where the ytterbium 4f eleetrons interact with the conduction electrons we observe Kondo-lattiee behavior at low temperatures. The onset of magnetie ordering expresses itself as a drop at low temperatures due to a decrease of spin disorder scattering. 

One calculates transport properties by correlating the resistivity with the total scattering cross-section. The electrical resistivity is found to be temperature insensitive at low temperatures, has the ln T/T ) dependence near T , and decreases steadily for T > Tq. The shape of the resistivity curve will be discussed in section 3.3. Clearly the low-temperature resistivity is in disagreement with experiments, which indicate the type Fermi liquid behavior. The discrepancy comes from the implicit assumption that the impurity atoms scatter the conduction electrons Incoherently. How the system achieves coherence at low temperatures is now studied in terms of the spin fluctuation resonance model, but the analysis has not yet reached the level of sophistication of the single-impurity problem. 

Once the energy bands are determined, the calculation of thermodynamic quantities is a simple exercise. The only complication is that the bands are temperature dependent and the Fermi energy /r(T) must be determined as a function of temperature. In contrast to the spin fluctuation resonance model, the present model has two energy parameters, namely r and /r(0). The interplay of these two parameters causes a breakdown of the simple scaling idea. For instance, it will be demonstrated that the thermodynamic properties are more sensitive to the quantity n(0) — r < r but the transport properties are more sensitive to tj. The exponent a also affects the result somewhat, but since a has a narrow range of variation, its influence on the results is weak. 

---