Observation of single-spin transport in an island-shaped CoFeB double magnetic tunnel junction prepared by magnetron sputtering

Abstract

The Co₄₀Fe₄₀B₂₀(CFB)/MgO/CFB/MgO/CFB-based multilayer was prepared by conventional magnetron sputtering and utilised in the fabrication of double magnetic tunnel junctions (DMTJs) for which the middle CFB layers were island-shaped. By analysing the magnetic property of the CFB islands with Langevin’s equation, it was possible to identify their diameters of 7.6, 8.9 and 11.0 nm; accordingly submicron-scaled DMTJs were fabricated to investigate single-spin transport phenomena. The coulomb staircase and the oscillatory tunnel magnetoresistive (TMR) were able to be observed at 6 K, where the TMR ratio was enhanced up to 60%, which is the highest value ever achieved in this structure.

Keywords:

• Magnetoresistance
• double magnetic tunnel junction
• coulomb staircase
• island growth

Acknowledgements

Author (TS) thanks Associate Professor Nobuki Tezuka and Dr. Tatsuya Saito for many fruitful discussions.

Additional information

Funding

This work was partly supported by Global COE program of Material Research Institute Tohoku University; KAKENHI (Grant-in-Aid for Young Scientists (A) [grant number 22686001]; Grant-in-Aid for Scientific Research (S) [grant number 24226001]; JST ‘Advanced Spintronic Materials and Transport Phenomena (ASPIMATT)’.