Parts | Days | Selection | Search | Downloads | Help
AM: Magnetismus
AM 7: Magnetische Schichten und Vielfachschichten III
AM 7.1: Invited Talk
Tuesday, March 18, 1997, 09:30–10:15, F5
Magnetic Nanoparticles — •S. Mørup — Technical University of Denmark, Department of Physics, DK-2800 Lyngby, Denmark
Nanometer-sized magnetic particles often exhibit fast superparamagnetic relaxation, i.e. fluctuations of the magnetization direction across the energy barriers, separating the easy directions of magnetization. By combining M"ossbauer spectroscopy measurements (with a time scale of the order of 1 – 10 ns) with ac and dc magnetization measurements (with time scales in the range 10−4 – 100 s) it is possible to obtain detailed information on the temperature dependence of the relaxation time. Moreover, the influence of inter-particle interactions can be studied. Because a large fraction of the atoms are in the surface, M"ossbauer spectroscopy can also be used to study surface magnetism in nanoparticles and how the surface atoms are affected by chemisorbed molecules. Studies of chemisorption on α-Fe particles show that chemisorbed oxygen leads to formation of a ferromagnetic iron oxide surface layer whereas carbon monoxide chemisorption results in a diamagnetic surface component.