Regensburg 2010 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 41: Nanoparticles and Composite Materials II

CPP 41.11: Talk

Thursday, March 25, 2010, 16:45–17:00, H48

Ferrofluids With Shifted Dipoles — •Rudolf Weeber, Sofia Kantorovich, Joan J. Cerdà, and Christian Holm — Institute for Computational Physics, Pfaffenwaldring 27, 70569 Stuttgart, www.icp.uni-stuttgart.de

In the last decades, ferrofluids and magnetic colloids have become relevant in many applications ranging from engineering to medicine, and therefore have attraced the interest of scientists from many fields. We present simulations and analytical calculations for a model system for magnetic nanoparticles that have a dipole moment shifted out of the center of mass, towards the surface. I.e., the spherical symmetry of the particle is broken. This model is inspired by experiments on colloidal particles with magnetic caps by Erbe et. al. While it does not attempt to reproduce the experiments exactly, similar structures can be observed already for intermediate shifts of the dipole. In our contribution, we discuss ground state properties for small clusters, which help us to understand the building blocks of larger systems. For moderate shifts of the dipole moment, the ground state structure changes from chains and rings with parallel alignment of moments, usually observed in dipolar particles, to pairs and triangles with close to anti-parallel orientation of moments. We also present magnetization properties of larger systems at finite temperature and observe the influence of the shift in particular on the initial slope of the magnetization curve, namely, the initial susceptibility.