Researchers from the NanoElectronics Research Institute (NeRI) of the National Institute of Advanced Industrial Science and Technology (AIST) and the Japan Science and Technology Corporation (JST) have developed a world-first TMR device that has a single-crystal nanostructured electrode and have discovered the new phenomenon of a spin-polarized resonant tunneling effect at room temperature. The findings pave the way for the development of new spintronic devices.

The discovery of a spin-polarized resonant tunneling effect at room temperature will facilitate the development of new devices (spin transistors) that possess both data storage and switching functions. The findings are expected to accelerate research into new MRAM (magnetoresistive random-access memory) technology that does not require semiconductor transistors. Moreover, such methods to control electron spin interference effects in solids could make a significant contribution toward the development of quantum computing.

1. First ever development of a TMR device that incorporates a single-crystal nanostructured electrode
   The researchers produced the first ever TMR device that generates a quantum well state and incorporates a nanostructured electrode made from a single-crystal non-magnetic metal (copper) and a ferromagnetic metal (cobalt).
    
2. Discovery of the spin-polarized resonant tunneling effect
   The researchers discovered a large oscillation in magnetoresistance when a quantum well state was formed in the electrode of a TMR device. The results demonstrate the new phenomenon of a spin-polarized resonant tunneling effect evev at room temperature.
    
3. Encouraging results for the development of spin transistors
   If this effect can be applied, it could enable the development of new TMR devices with additional switching functionality.
    
4. The results are published in the 12 July 2002 edition of the US journal Science:
   Article title: Spin-Polarized Resonant Tunneling in Magnetic Tunnel Junctions
   [Authors: S. Yuasa, T. Nagahama, Y. Suzuki]
    

This research was based on a collaborative research agreement between AIST and JST and was carried out as a project for Core Research for Evolutional Science and Technology (CREST) in the area of Functional Control of Electrons, Photons, Etc. as part of the research theme Creating Novel Functions by Spin Injection in Solids.

Figure1(A): Conventional TMR device.	Figure1(B): New type TMR device with an electrode made of single-crystal nanostructure.
Figure2: Electron microscopy image of the new type TMR device with a nano-structured electrode, which consists of single-crystal layers of nonmagnetic copper and ferromagnetic cobalt.
Figure3: Schematic diagram of the new type TMR device with a nanostructured electrode, in which electrons with different spin directions tunnel from the upper to the bottom electrodes. The arrows pointing to the right and the left denote the directions of electron spins. Only the electron spins pointing to the left are confined in the copper layer and form spin-polarized quantum-well.
Figure4: Magnetoresistance exhibits a large oscillation as a result of the spin-polarized resonant tunneling. It is noteworthy that the spin-polarized resonant tunneling occurs even at room temperature.