Semiconductor-based tunnel structures: preparation and application


Semiconductor-based tunnel structures: preparation and application

Zhou, S.; Schmidt, H.

Spin-polarized tunnel magnetoresistance (TMR) effects occur when two ferromagnets are separated by a thin insulator. The resistance of the tunneling current changes with the relative magnetization orientation of the magnetic bottom and top electrode [1,2]. The research in this field is fuelled by the demanding of magnetoresistive random access memory (MRAM) devices. In 2004, Parkin et al. were able to make Fe/MgO/Fe junctions with 200% TMR at room temperature [3]. However, the development of high-density metal-based MRAM scale devices is hampered by large switching fields and multidomain structures. Theoretically, diluted magnetic semiconductors (DMS) reveal a larger degree of spin polarization and therefore also bigger spin transport effects. Mn-doped GaAs is a successful DMS and magnetic tunnel junctions based on epitaxially grown GaMnAs/AlAs/GaMnAs have shown promising TMR values up to 75% at 8 K [5]. Novel MRAM cells are based on magnetic tunnel junctions with current-induced switching. It has been shown that semiconductors [6] need a current pulse for switching which is two orders of magnitude smaller in comparison to metals [7]. Using wide-gap magnetic semiconductors, e.g. ZnO, the magnetic tunnel structure may be transparent and may possess a Curie temperature above room temperature [9,10].

In this talk, we report the clearly observed tunneling magnetoresistance at 5 K in magnetic tunnel junctions with Co-doped ZnO as the bottom electrode and Co as the top electrode prepared by pulsed laser deposition and thermal evaporation [11], respectively. Spin-polarized electrons were injected from Co-doped ZnO to the crystallized Al2O3 separation layer and tunnelled through the amorphous part of the Al2O3 barrier. Our studies demonstrate the spin polarization in Co-doped ZnO and its possible application in future ZnO-based spintronics devices. Additionally, we will show preliminary results of Si:Mn based tunnelling structures. In this system, SiO2 is the barrier layer while ferromagnetic granular Si:Mn obtained by Mn ion implantation into Si and Co are the bottom and top electrode, respectively.

[1] J. S. Moodera et al., Phys. Rev. Lett. 74, 3273 (1995).
[2] T. Miyazaki et al., J. Magn. Magn. Mater. 139, L231 (1995).
[3] S. S. P. Parkin et al., Nat. Mat. 3, 862 (2004).
[4] S. D. Sarma et al., Solid State Commun. 119, 207 (2001).
[5] M.Tanaka et al., Phys.Rev. Lett. 87, 026602 (2001).
[6] M. Yamanouchi et al., Nature 428, 539 (2004).
[7] J.A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000).
[8] T. Jungwirth et al., Phys. Rev. B 72, 165204 (2005).
[9] T. Dietl et al., Science 287, 1019 (2000).
[10] K. Sato et al., Jpn. J. Appl. Phys. 39, L555 (2000).
[11] Q. Xu et al., Phys. Rev. Lett. 101, 076601 (2008)

  • Invited lecture (Conferences)
    International Workshop on Advances in Spintronic Materials: Theory and Experiment, 26.-28.11.2008, Duisburg, Germany

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Publ.-Id: 11978