Berlin 2005 – wissenschaftliches Programm

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MA: Magnetismus

MA 20: Poster:Schichten(1-29),Spintrsp(30-45),Ex-Bias(46-63),Spindyn(64-75),Mikromat.(76-80),Cluster(81-94),Abbv.(95-99),Obflm(100-02),SpElek.(103-09),E-Theo(110-14),Mikromag.(115-16),Spin+PÜ(117-26),Mag.Mat.(127-51),Meth.(152-55),Mol.Mag(156-59),Kondo(160-65

MA 20.90: Poster

Montag, 7. März 2005, 14:00–18:00, Poster TU C

Magnetization measurements on frozen ferrofluids - an attempt to separate interaction and anisotropy influences — •H. Bremers, O. Michele, and J. Hesse — Institut für Metallphysik und Nukleare Festkörperphysik, Technische Universität, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany

In this contribution we focus on a novel way to perform magnetization experiments on frozen ferrofluids or magnetic nanoparticles fixed in space. The basic idea is to project the behaviour of a real particle system onto a Stoner-Wohlfart (SW) particle ensembly behaviour. Therefore first an ideal SW particle system with unique size and orientation of easy axis was studied numerically by introducing a particle - particle interaction via an demagnetizing field. We have shown that for non-interacting SW particles the universal mean value rule holds that the magnetization measured after ZFC (zero field cooling) can be expressed as a mean value of the magnetization measured after PHFC and NHFC (positive and negative high field) [1] cooling processes. Any deviation from this mean value rule is due to interactions only and can be derived from the magnetization measurements and assigned to equivalent behaviour of a SW particles system. By this new method it is possible to determine the mean value of the particles anisotropy and the mean interaction which is expressed as magnetic field. [1] O. Michele, J. Hesse, H. Bremers, E.K. Polychroniadis, K.G. Efthimiadis, H. Ahlers; J. Phys.: Cond. Matter 16 (2004) 427-443