Tuning the magnetic interactions in GaAs:Mn/MnAs hybrid structures by controlling shape and position of MnAs nanoclusters

Thumbnail Image

Files

ElmMatthias_2010_11_19.pdf (10.69 MB)

Date

2010

Authors

Advisors/Reviewers

Further Contributors

Contributing Institutions

Publisher

Journal Title

Journal ISSN

Volume Title

Publisher

License

In Copyright
In Copyright

Quotable link

DOI:
http://dx.doi.org/10.22029/jlupub-9601

Abstract

The realization of magnetoelectronic and spintronic devices is recently of great interest because such devices not only use the charge of the electron for information processing and storage, but also its spin. This provides an enhanced functionality such as the non-volatile storage of information in so-called MRAMs.An interesting material system for the realization of new magnetoelectronic devices are the so-called granular hybrid structures consisting of ferromagnetic nanoclusters, which are embedded in a paramagnetic matrix. These hybrids have the advantage that they combine ferromagnetic and semiconducting properties in one single material system. In addition, they show magnetoresistance effects similar to the giant or tunnel magnetoresistance, which nowadays are widely used in e.g. non-contact sensors or hard disk read heads. In general, mainly the random cluster distribution of conventionally grown hybrid structures hinders a technological utilization of these effects in miniaturized magnetoelectronic devices.However, with the new method of self-assembled growth by selective area metal-organic vapour phase epitaxy (SA-MOVPE) on pre-patterned (111)B-substrates, regular arrangements of nanoclusters of well-defined size, shape and position can be prepared.In this work the magnetic properties of hexagonal MnAs nanoclusters and their influence on the transport properties of GaAs:Mn /MnAs hybrid structures were studied. Various arrangements of isolated nanoclusters and cluster chains were grown on (111)B-GaAs substrates by SA-MOVPE. The first part of this work deals with the manufacturing process of the different cluster arrangements investigated. By a suitable pre-structuring of the substrate it was possible to influence the cluster size, cluster shape and cluster position systematically. Preparing various arrangements it could be shown that the hexagonal nanoclusters prefer to grow along their a-axes.In the second part, the magnetic properties of the nanoclusters were studied. Ferromagnetic resonance (FMR) measurements show a hard magnetic axis perpendicular to the sample plane, i.e. parallel to the c-axis. By measurements, where the magnetic field was rotated in the sample plane, it could be demonstrated that the orientation of the magnetization can be forced into a certain direction by controlling the cluster shape. These results are confirmed by measurements using magnetic force microscopy.The third part deals with the influence of the nanoclusters and their arrangement on the transport properties of the GaAs:Mn matrix. For temperatures above 30 K the structures investigated show positive as well as negative magnetoresistance effects, which are typical for granular GaAs:Mn/MnAs hybrid structures. This behaviour can be explained in the context of transport in extended band states. The size of the magnetoresistance effects correlates strongly with the respective cluster arrangement of the sample. This behaviour has been predicted theoretically and could be confirmed experimentally in the context of this work.Below 30 K large positive magnetoresistance effects show up for the regular cluster arrangements, which cannot be observed for hybrid structures with random cluster distributions. These large positive magnetoresistance effects and their qualitative behaviour with increasing magnetic field can be attributed to so-called hopping transport, which dominates at these temperatures. In addition at low temperatures, the size of the respective effects strongly correlates with the cluster arrangement. By angle-dependent measurements, in which the external magnetic field was rotated in the sample plane, a direct influence of the orientation of the cluster magnetization on the transport properties could be demonstrated.

Link to publications or other datasets

Description

Notes

Original publication in

Original publication in

Anthology

Collections

Dissertationen/Habilitationen

URI of original publication

Forschungsdaten

Series

Citation