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Magnetoresistance in Co/AlOx/Co tunnel junction arrays
KTH, Superseded Departments, Physics.
KTH, Superseded Departments, Physics.ORCID iD: 0000-0003-2339-1692
KTH, Superseded Departments, Physics.ORCID iD: 0000-0001-8534-6577
2002 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, Vol. 249, 513-518 p.Article in journal (Refereed) Published
Abstract [en]

Lateral arrays of Co/AlOx/Co junctions with dimensions down to 60 nin and inter-junction separations similar to60-100 nm have been fabricated and analyzed for possible coherent tunneling effects. Extra attention is paid to avoid uncertainties due to inconsistencies in switching and/or resistance of successive barriers. We observe similar to10% magnetoresistance enhancement at moderate bias in double junctions that cannot be accounted for by a simple model of two resistsors in series.

Place, publisher, year, edition, pages
2002. Vol. 249, 513-518 p.
Keyword [en]
magnetoresistance, magnetic nanostructure, tunnel junction array, Co, AlOx
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-5414DOI: 10.1016/S0304-8853(02)00457-2ISI: 000179065800022OAI: diva2:9775
QC 20100924Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2010-09-24Bibliographically approved
In thesis
1. Spin-dependant transport in lateral nano-devices based on magnetic tunnel junctions
Open this publication in new window or tab >>Spin-dependant transport in lateral nano-devices based on magnetic tunnel junctions
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis is an experimental study of spin dependent transport in nanoscale ferromagnetic tunnel junction arrays and lateral multi-terminal devices with normal metal and superconducting spin transport channels.

Two-, three-, and five-junction arrays have been fabricated in the form of lateral circuits and characterized using variable temperature magneto-transport measurements. The smallest inter-junction separation achieved was 65 nm. No significant enhancement in the sequential magneto-resistance (MR) was observed, which is attributed to the combined effect of short spin diffusion length in the ferromagnetic electrodes and high resistance of the tunnel barriers used. A substantially weaker bias dependence of the MR is observed for double junctions than for single junctions, consistent with the theoretical expectations.

Spin diffusion and relaxation in one-dimensional normal metal channels is studied using a novel multi-terminal device. The device has multiple ferromagnetic detector electrodes for an in-situ determination of the spin transport parameters. Such configuration has a great advantage as it eliminates sample-to-sample uncertainties in the physical properties studied. A three terminal device having a pair of detector electrodes placed symmetrically about the injection point is used to directly demonstrate decoupling of spin and charge current in nanostructures. Furthermore, by varying the thickness of the normal metal channel on the scale of the mean free path the surface contribution to spin relaxation is measured and compared to the bulk spin scattering rate. It is found that for Al surface scattering makes a weak contribution to the overall spin relaxation rate, the result that should be important for a number of proposed thin film spin-based devices.

The interplay between non-equilibrium magnetism and superconductivity is studied in a ferromagnetic/superconductor single electron transistor. Spin imbalance in the base is controlled by the bias voltage applied to the magnetic emitter/collector as well as the relative orientation of their magnetic moments. A strong magneto-transport effect is observed and attributed to a suppression of the superconducting gap in the center electrode by the spin imbalance in the antiparallel state of the device. The intrinsic spin relaxation parameters for the center electrode, important for interpreting the data are studied in a separate experiment using spin injection into a one-dimensional superconducting channel. It is found that the spin accumulation increases substantially on transition into the superconducting state while the spin diffusion length is reduced. These results represent a new way of combining magnetism and superconductivity on the nano-scale.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. iv, 86 p.
Trita-FYS, ISSN 0280-316X ; 2006:08
Spin diffusion, magnetic tunnel junctions
National Category
Physical Sciences
urn:nbn:se:kth:diva-3866 (URN)91-7178-278-8 (ISBN)
Public defence
2006-03-17, FR 4, Oskar Klein, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
QC 20100924Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2012-02-10Bibliographically approved

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