Dresden 2006 – scientific programme

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MA: Magnetismus

MA 16: Micro- and Nanostructured Magnetic Materials II

MA 16.1: Talk

Tuesday, March 28, 2006, 11:45–12:00, HSZ 103

In-situ measurements of magnetoresistive effects in ferromagnetic microstructures by Lorentz TEM — •Thomas Haug, Anton Vogl, Josef Zweck, and Christian H. Back — Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany

Recently large magnetoresistive values exceeding 10.000% have been discovered in ferromagnetic nanocontacts. In these experiments it is assumed that the contact area supports almost atomically sharp domain walls, where the conduction electrons suffer strong spin scattering. However, this theory is discussed controversially, as some other reasons could be listed as well, which might explain these extraordinary high effects. Apart from that, many other magnetoresitive experiments can only be explained theoretically or on the basis of micromagnetic simulations. So there is a strong need for direct observation of the micromagnetic behavior of the samples during the magnetoresistance measurement. We report on a four point resistance measurement inside a transmission electron microscope (TEM) and during the imaging process which uses a newly developed specimen holder. Lorentz microscopy allows us to observe the micromagnetic configuration of the ferromagnetic samples. Two different imaging techniques, Fresnel imaging and differential phase contrast (DPC) are used. The latter one allows lateral magnetic resolution down to 10 nm. We present first experiments on ferromagnetic Nickel structures where we can show the direct correlation between the appearance of magnetic domains and anisotropic magnetoresistance.