Dresden 2006 – wissenschaftliches Programm
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MA: Magnetismus
MA 11: Spin-Structures and Magnetic Phase Transitions II
MA 11.1: Vortrag
Montag, 27. März 2006, 15:00–15:15, HSZ 403
Magneto-optic measurement of magnetic phase transition and domain structure of liquid Co80 Pd20 — •Lucian M. Stefan and Karl Maier — Helmholtz Institut für Strahlen- und Kernphysik, Rheinische Friedrich-Wilhelms-Universität Bonn, Nußallee 14-16, D-53115 Bonn, Germany
The temperature dependence of the magnetisation of liquid Co80 Pd20 was obtained and the domain structure of the liquid phase was investigated. The spherical samples (mass: 10 - 11mg) were processed in an electromagnetic levitation device in pure H2 atmosphere, which allows an undercooling of Δ T ≈ 360K below the liquidus temperature (T = 1610K). The magnetisation on the surface across the magnetic phase transition was measured via the magneto-optical Kerr effect.
A significant increase of the Kerr-angle was observed at the magnetic phase transition which reflects the appearance of magnetic order in the liquid. The Curie temperature found for the liquid phase is TCl = 1253K and compares to similar values found in earlier experiments (stray field measurements). All Kerr data indicate a plateau in a region of ≈ 0.5K at the low-temperature end of the magnetisation curve. This is interpreted as the presence of an identical domain structure in all independent measurements (measuring area diameter about 10µ m). Our results agree with computer simulations, which predict a vortex structure of domains for a liquid spherical sample. In this structure the spins are oriented parallel to the surface along an imaginary equator due to the absence of domain walls in a ferromagnetic liquid.