Spin - Polarized Low - Energy

SPLEED Spin-Polarized Low Energy Electron Diffraction Similar to LEED, except the incident electron beam is spin-polarized. This is particularly useful for the study of surface magnetism and magnetic ordering. 

Spin-polarized low-energy SPLEED electron diffraction... 

Spin-polarized low-energy electron diffraction (24, 145) Scanning tunneling microscopy (2, 35, 146-152)... 

Magnetic Measurements. Our method of choice to measure the coupling behavior was spin-polarized secondary electron emission (SPSEE). After bombardment with 1 keV electrons, spin-polarized low-energy electrons are emitted. The spin analysis is carried out by a Mott detector. The secondary electrons are emitted from the first few layers only and the method is thus surface sensitive. 

Figure 7.2 Diffraction of spin-polarized low energy electrons (SP-LEED). (a) Schematic description of the experimental phenomenology, (b) Evaluation of the reflected intensities ia depending on the direction of spin polarization (a = -h or —) and magnetization p, = + or —) with respect to the normal of the scattering plane [3].

The techniques of u.SR and p-LCR are based on the fact that parity is violated in weak interactions. Consequently, when a positive muon is created from stationary pion decay its spin is directed opposite to its momentum. This makes it possible to form a beam of low energy (4 MeV) positive muons with nearly 100% spin polarization at high intensity particle accelerators such as TRIUMF in Canada, the PSI in Switzerland, LAMPF and BNL in the USA, KEK in Japan, and RAL in England. Furthermore the direction of position emission from muon decay is positively correlated with the muon spin polarization direction at the time of decay. This allows the time evolution of the muon spin polarization vector in a sample to be monitored with a sensitivity unparalleled in conventional magnetic resonance. For example, only about 101 7 muon decay events are necessary to obtain a reasonable signal. Another important point is that //.SR is conventionally done such that only one muon is in the sample at a time, and for p,LCR, even with the highest available incident muon rates, the 2.2 fis mean lifetime of the muon implies that only a few muons are present at a given time. Consequently, muonium centers are inherently isolated from one another. 

In Fig. 7 the results of the model for the cohesive energy are given, and compared with the experimental values and with the results of band calculations. The agreement is satisfactory (at least of the same order as for similar models for d-transition metals). For americium, the simple model yields too low a value, and one needs spin-polarized full band calculations (dashed curve in Fig. 7) to have agreement with the experimental value. 

For a particle with an energy E, the effective gap seen is A — E. At low temperatures, we can take into account the excess resistance due to charge imbalance by introducing an effective voltage dependent charge imbalance time tq caT/(A — eV), and adding a resistance Rq = PaAq to the resistance calculated in the spin-polarized BTK model described above. 

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