Title: " Exploiting magnetic dipolar interactions in artificially nanostructured systems "

Thesis supervisor: Paolo Vavassori

When: 7 February, Friday, 11:00

Where: Korta Building

Abstract: 

This PhD thesis deals with the study of magnetic dipolar interactions in different ferromagnetic nanostructured materials. After an introduction to ferromagnetism at the nanoscale, the nanofabrication method used to pattern the nanostructures issue of study in this thesis is presented. By means of Electron-Beam Lithography, well-defined ferromagnetic nanostructures with sub-50nm gaps between neighbouring nanoelements have been fabricated in a fully controlled and reproducible fashion. After that, three different cases where magnetic dipolar interactions play a predominant role are presented. The first case consists in studying the magnetization reversal process in elongated ferromagnetic nanoelements coupled through asymmetric dipolar interactions, due to which it is possible to tune the magnetization reversal pathway. Depending on the orientation of the externally applied field it is possible to induce the formation of stable non-uniform magnetization states at remanence in nanomagnets where these non-uniform states are energetically extremely unfavoured with respect to a single-domain state. The second case consists of studying the physics of the accommodation of frustration in so-called Artificial Spin-Ice nanostructures. Different demagnetization protocols have been proposed in literature to study how the magnetization of the nanoelements is accommodated. In this thesis a thermal demagnetization protocol never reported previously in literature is presented: with this demagnetization protocol systematic studies of the accommodation of frustration in Artificial Spin-Ice samples become possible. The third case deals with the study of the effect of ultrafast dipolar magnetic field pulses, created by the displacement of a domain wall through a nanostripe, on the magnetization of adjacent magnetic nanoellipses placed at a distance of 50nm from the nanostripe. A magnetization reversal process in these nanoellipses is induced, provoked by the action of the ultrafast magnetic field pulse created by the domain wall being displaced through the nanostripe.