Spin-Polarized Ion Scattering Spectroscopy
Before this system was developed, it was very difficult to analyse magnetic structure of outermost surfaces even with the most advanced analytical techniques. In order to develop spintronics devices (employing both charge and spin) further, it was necessary to realize the analysis of "Spin" and "structure" at the ourtermost surface (first aomic layer at the surface).
Generation of spin-polarized 4He+ ion beam made the impossible possible. This beam is the key technology to SP-ISS. The NIMS reseacher succeeded in generation of world's highest beam performance index (beam polarization). By using this beam, dramatic progress in spintronics development is expected in the future
Applications
HDD, MRAM (Magnetoresistive Random Access Memory) [TMR (Tunnel Magneto-Resistance), GMR (Giant Magnet-Resistance)]
How It Works
The figure above shows the principle of spin analysis of outermost surfaces using the spin-polarized 4He+ ion beam. When He+ ions are scattered at a surface, electrons are captured by He+ at the outermost surface and the ions become He atoms (ion neutralization). However, the occurrence of neutralization is limited to cases where the spin orientations of the He+ ion and the electrons of the outermost surface are anti-parallel (Pauli exclusion principle). In (A), the He+ ion is neutralized, but in contrast, in (B), neutralization does not occur. In other words, because neutralization depends on the spin of ther outermost surface electrons, the electron spin of the outermost surface can be analyzed by measuring the He+ ions which are scattered without undergoing ion neutralization.
Spin-Polarized 4H+ Ion Beam
This beam is very sensitive to both outermost surface and spin. The beam quqlity of this system is the best in the world.
P = 25 %
I = 5 nA
After a few years research, the quality has been improved very much. 25% of spin polarization ratio is the world's highest value.
Generation of the beam
- Generate metastable He atom (He* (23S1, 1s2s)) by electric discharge
- Make He* spin polarized by optical pumping at 1083 nm
- Penning ionization : He* + He* --> He+ + He0 +e-
Schematic of Optical Pumping
