Dresden 2011 – scientific programme

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MA: Fachverband Magnetismus

MA 43: Micro- and Nanostructured Magnetic Materials IV

MA 43.8: Talk

Wednesday, March 16, 2011, 18:45–19:00, HSZ 103

Examination of the Switching Field Distribution (SFD) and the shape anisotropy constant of nickel nanorods — •Florian Krämer, Philipp Bender, Andreas Tschöpe, and Rainer Birringer — Universität des Saarlandes, Saarbrücken

Nickel nanorods with diameters D<64nm and aspect ratios n>3 are expected to be uniaxial ferromagnetic single domain particles. The most simple approach to estimate their magnetic behavior is the Stoner-Wohlfarth-Modell (SWM), where magnetic reversal of ellipsoidal particles is assumed to occur by delocalized coherent rotation. However measurements of Ni nanorods show that their coercivity is significantly smaller than predicted by the SWM. There are two possible explanations for this discrepancy: first, a reduced shape anisotropy constant, and second, deviations from the proposed delocalized coherent rotation.The objective of this work was to study the magnetism of Ni nanorods with varying geometry (D=12−22 nm, n>5), in terms of their switching field distribution and shape anisotropy constant.The Ni nanorods were synthesized by current-pulsed electrodeposition of Ni into hexagonally ordered porous alumina templates. The nanorods were released from the templates by dissolution of the alumina in aqueous NaOH and dispersed in gelatine solutions (10 wt% gelatine) at 60 ^∘C. Applying an external homogenous magnetic field during gelation enables the preparation of magnetically textured ferrogels with negligible dipolar interaction between the rods.The shape anisotropy constant and SFD’s of the nanorods were determined from static magnetization measurements of the uniaxial ferrogels.