Magnetic characterization of single nanostructures

CIC nanoGUNE Seminars

Hans Peter Oepen. University of Hamburg, Hamburg, Germany
nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
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Magnetic characterization of single nanostructures In this talk new approaches are presented to study the magnetic behavior of single nanostructures and the interaction between nanostructures. In principal a micro- or nanoscaled device is built that gives access to the magnetic properties of individual nanostructures. To quantify the interaction between nanostructures exhibiting flux closure domain pattern we have developed a new technique to study the magnetization behavior in single elements. Utilizing a highly focused ion beam (FIB) we create structures in a thin film including electrical contacts, which allows to measuring the energy state of the individual element via the anisotropic magnetoresistance. The sizes of the magnetic Py structures vary between 300 x 600 nm2 and 500 x 1000nm2. The energy of the magnetic ground state is measured via the reversal magnetization behavior on applying a magnetic field along the short axis of the rectangles. When identical elements are positioned next to the rectangle the magnetization behavior changes depending on the separation between the structures. This is used to quantify the interaction between the elements. To fabricate smaller structures with diameters below 20 nm we use low energy ion milling to structure thin films or multilayers. For that purpose we deposit nanosized particles on Co/Pt multilayers. The particles protect the magnetic multilayers locally from being removed by ions while between the particles the magnetic multilayer is erased. On applying the correct dose an array of magnetic multilayer dots is created. The anisotropy and the total amount of magnetic material per nanodot can be purposely tuned so that the magnetic property of the dots can be varied from ferromagnetic to superparamagnetic behavior. The magnetization behavior of the dots is determined utilizing the Anomalous Hall Effect (AHE). To attain a Hall voltage crosses are fabricated by lithographical methods on which the multilayer is deposited. Performing the above mentioned procedures of transferring the nanoscale structure into the film we generate Hall geometries that contain only very small amounts of nanoparticles. Up to now we were able to measure the magnetic behavior of ensemble with a minimal number of about 18 nanodots. Based on our experience we estimate that the technique has the potential for the investigation of single nanodots magnetization behavior.