Magnetische Anisotropie und Spintransport in magnetoelektronischen Schichtsystemen und Nanostrukturen

The increasing use of information technology has lead to the development of numerous new concepts and processes in the production of electronic devices and magnetic data storage systems. The preparation and lithographic patterning of thin films plays a central role in this context. This work was motivated by the progress in these fields. The focus lies on the magnetic anisotropy and preparation of magnetotransport structures.The theoretical basis of magnetic anisotropy and magnetotransport is explained in chapters 1 and 2. Experimental methods and setups used for this work are introduced in chapter 3. In chapter 4 an analysis of the magnetic anisotropy of Fe(110) thin films on sapphire substrates with a Mo(110) buffer is shown. Samples with different Fe(110) layer thicknesses were grown by molecular beam epitaxy (MBE) and examined ex situ by Brillouin light scattering (BLS). The frequency of the Damon Eshbach spin wave mode was measured for each thickness as a function of the angle between the external magnetic saturation field and a selected in plane direction of the sample. By fitting the spin wave frequency with a continuum model the relevant magnetic anisotropy constants were extracted. A dependence of the magnetocrystalline anisotropy and a uniaxial in-plane anisotropy on the thickness could be observed which is attributed to anisotropic relaxation of lattice distortion in the Fe(110) layer.A magnetooptical Kerr effect (MOKE) study of micropatterned exchange bias systems with perpendicular magnetic anisotropy introduced in chapter 5 shows that perpendicular anisotropy as well as exchange bias are influenced, but not destroyed by the patterning process. Structures in the range of 200 nm to several microns were prepared and examined. The coercivity of the microstructures grows with decreasing lateral dimension, while the exchange bias is reduced. The comparison of the temperature dependence of coercivity and exchange bias in microstructures and an unpatterned reference sample indicates an influence of patterning on the distribution of local blocking temperatures. In chapter 6 two different methods of preparing transport structures on the micrometer to nanometer scale are introduced. The operativeness of the devices is proven by magnetotransport measurements. The first introduced process allows the preparation of current perpendicular to the plane (cpp) devices from pre-deposited multilayer samples. Tunneling magnetoresistance (TMR) structures based on ferromagnet/insulator/ferromagnet layer systems were prepared which showed a TMR ratio of up to 45% at room temperature.The second process developed in this work allows the fabrication of cpp contacts with lateral dimensions of 100 nm and less. Nanostencils are pre-patterned to define the geometry and dimension of the contacts which are prepared by depositing a multilayer onto the nanostencil. With samples prepared by this method it was possible to show switching of the electrodes of a giant magnetoresistance (GMR) nanocontact by spin torque transfer. Measurements were performed under different external magnetic fields. Current-induced excitation of the spin system in the contacts could be observed.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2006

Author dc:creator

• Fraune, Michael

Contributors dc:contributor

• Güntherodt, Gernot

• info:eu-repo/classification/ddc/530
• Physik
• Magnetische Anisotropie
• Magnetowiderstand
• Lithographie
• Magnetooptik
• Ionenstrahllithographie
• magnetic anisotropy
• magnetooptics
• magnetoresistance, lithography
• focussed ion beam lithography

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123774%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:62185