Berlin 2008 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 16: SYM Phase Transformations in Metallic Melts V
MM 16.3: Vortrag
Dienstag, 26. Februar 2008, 10:45–11:00, H 1058
Nanosized magnetisation density profiles in hard-magnetic NdFeCoAl glasses — •A. Wiedenmann1, O. Perroud1, M. Stoica2, and J. Eckert2 — 1HMI-Berlin, Glienickerstr. 100, 14109 Berlin — 2IFW-Dresden, P.O. Box 270116, 01171 Dresden
Nd-Fe-Co-Al alloys have a high glass forming ability and show hard magnetic behavior at room temperature. The aim of the present SANS investigation was to establish structural and magnetic units in the alloys on a nanometer length scale and correlate them with the observed magnetic properties. Nd80Fe20 and Nd60FexCo30−xAl10 cylinders with x=0, 7.5 and 20 have been produced by mold casting with different diameters and have been investigated by SANS, SEM/TEM and magnetization measurements. The microstructure consists of a Nd-rich matrix, a Fe-rich partially amorphous phase and of nanosized Nd particles. The magnetisation show two transition temperatures: Tc1∼40K corresponds to the ordering of the magnetic moment in the Nd phases and and Tc2∼500K to the Curie temperature of the Fe-rich phase. The low magnetic scattering contribution has been extracted beside the strong nuclear scattering by using polarized neutrons. It turned out that the Fe-rich phase is essential for the hard magnetic properties of the alloys where the nanoparticles play an important role, while the Fe free alloy is soft magnetic. The magnetization density profil depends on T: Well below Tc1 the local magnetization of the nanosized particles is higher than that of the ferromagnetic matrix while above Tc1 they are paramagnetic and act more efficiently as pinning centers for the magnetic domains, which enhance the coercivity above Tc1.