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All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics
Published on: January 19, 2018
Tunneling magnetoresistance on the subnanometer scale
Christian Heiliger1, Martin Gradhand, Peter Zahn
1Department of Physics, Martin Luther University Halle-Wittenberg, D-06099 Halle, Germany.
Physical Review Letters
|October 13, 2007
Summary
The structure of iron (Fe) electrodes significantly impacts the tunneling magnetoresistance (TMR) ratio. A single crystalline Fe layer adjacent to the barrier dramatically boosts TMR, even with amorphous Fe present.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Quantum Mechanics
Background:
- Tunneling Magnetoresistance (TMR) is crucial for magnetic sensor technology.
- The electrode-barrier interface critically influences TMR device performance.
- Understanding the role of electrode structure is key to optimizing TMR devices.
Purpose of the Study:
- To investigate the effect of iron electrode thickness and structure (amorphous vs. crystalline) on the TMR ratio in Fe/MgO/Fe tunnel junctions.
- To determine the minimum crystalline structure required for achieving high TMR.
- To elucidate the underlying physical mechanisms governing TMR in these systems.
Main Methods:
- Ab initio calculations were employed to simulate Fe/MgO/Fe tunnel junctions.
- The electronic structure and transport properties were analyzed.
- The influence of amorphous and crystalline iron layers of varying thicknesses was systematically studied.
Main Results:
- An amorphous Fe layer directly contacting MgO results in a low TMR ratio (44%).
- Inserting even a single crystalline Fe monolayer between the amorphous Fe and MgO barrier significantly increases the TMR ratio.
- A giant TMR ratio exceeding 500% is achievable with just one crystalline Fe monolayer.
- Amorphous Fe has minimal impact if more than two crystalline Fe monolayers are present.
- The TMR effect originates from symmetry selection within the MgO barrier and spin filtering at the Fe-MgO interface.
Conclusions:
- The crystalline structure of Fe electrodes, particularly at the interface with the MgO barrier, is paramount for achieving high TMR ratios.
- A single crystalline Fe monolayer is sufficient to engineer a giant TMR effect.
- The TMR phenomenon in these junctions arises from a combination of quantum mechanical effects within the barrier and at the electrode interface, independent of the bulk electrode magnetism.
