Dresden 2009 – scientific programme
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MA: Fachverband Magnetismus
MA 40: Poster II: Bio- and Molecular Magnetism (1-9); Magnetic Coupling Phenomena/Exchange Bias (10-15); Magnetic Particlicles and Clusters (16-29); Micro and Nanostructured Magnetic Materials (30-51); Multiferroics (52-64); Spin Injection in Heterostructures (65-67); Spin-Dyn./Spin-Torque (68-93); Spindependent Transport (94-108)
MA 40.23: Poster
Friday, March 27, 2009, 11:00–14:00, P1A
Magnetoelastic effects of magnetic nanoparticles in a copolymer matrix — •W. Schirmacher1, A. Omran2, L. Schulz3, S. Vallopilly4, P. Böni2, W. Petry2, and P. Müller-Buschbaum2 — 1Institut für Physik, Universität Mainz — 2Physik-Department E13, TU München — 3Universite de Fribourg, Switzerland — 4LENS Indiana Synchrotron Facility, Bloomington IN, USA
Magnetic properties of thin composite films, consisting of polystyrene-coated γ-Fe2O3 (maghemite) nanoparticles embedded into polystyrene-block-polyisoprene (PS-b-I) matrices, have been investigated. The magnetization measured as a function of external field and temperature show typical features of “super-paramagnets”, including a hysteresis at low temperatures and dispersive blocking, as expected for polydispersive samples. However, the differential magnetic susceptibility depends only weakly on temperature between roomtemperature and 2K. This strongly contradicts the superparamagnetic model, for which a Curie law is expected. We are able to explain our findings if we assume a mechanical twist of the particle due to the applied field. This coupling mechanism yields a temperature-independent susceptibility which is inversely proportional to the shear modulus of the copolymer matrix. We are able to successfully fit the hysteresis curves of our samples with this model.