Our in-situ MR-setup allows investigating the magnetization behaviour of single submicron structures, which have been prepared within the same chamber by means of a highly focused ion beam (FIB), via magnetotransport measurements. Up to now we concentrated on rectangles that have been prepared out of a chromium/permalloy/platinum trilayer film system.
To investigate the rectangles, a several microns sized electrical circuit has been prepared like it is shown in figure 1. The bright gray rectangle (1) is the ferromagnetic structure that is to be investigated. Above from there is a contact pad (6), which we can place a submicron tungsten tip via a nanometer-precision micromanipulator at (link in-situ MR). To decouple the structure and the ferromagnetic film, the area around the rectangle (3) has been rendered paramagnetic by ion irradiation, without decreasing the electric conductivity too much. If now a voltage is applied between the tip and the film (2), the isolation (4 und 5) around the contact pad forces the whole electrical current to run through the ferromagnetic rectangle. The potential difference between the tip and the film is beeing measured in dependence of an externally applied magnetic field to investigate the magnetization behavior.
The dominating so called anisotropic magnetoresistance (AMR) is used for our investigation. We obtain the following magnetoresistance curves according to the magnetic field being either parallel to the long axis of the rectangle (easy axis of magnetization, figure 2) or perpendicular to it (so parallel to the hard axis of magnetization, figure 3):
The SEMPA images point out the changes in the magnetic microstructure of the rectangles in an external field. In the case of easy axis loops steps in the magnetoresistance appear, which can be linked to irreversible transitions between quasi single domain s- or c-states and the so called diamond state (see fig 4). In the case of hard axis loops just reversible processes occur: The size of the end domains and the angle of the magnetization in the main domains are changed by the magnetic field like it's shown in fig. 5.
