Structure, microstructure and magnetic properties of electrodeposited Co and Co-Pt in different nanoscale geometries

Thin films and nanowires of Co-Pt have been prepared by means of electrodeposition. Composition, structure, microstructure and magnetic properties have been intensively studied using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry and correlated to the deposition parameters such as electrolyte composition, deposition current and/or potential. Co rich Co-Pt films have been deposited at various current densities. A nearly constant composition of Co70Pt30 was achieved for current densities between 18 and 32 mA/cm². Detailed texture measurements confirmed an increasing fraction of the hexagonal phase with its c-axis aligned perpendicular to the film plane with increasing current density. Accordingly, magnetic properties are strongly affected by the magnetocrystalline anisotropy of the hexagonal phase that competes with the shape anisotropy of the thin film geometry. Co-Pt nanowires have been prepared within alumina templates at different deposition potentials between -0.6 and -0.9VSCE changing the composition from nearly pure Pt to Co. The composition Co80Pt20 was observed at a deposition potential of -0.7VSCE. Co-Pt nanowires are nanocrystalline in the as-deposited state. Magnetic measurements reveal changing fcc and hcp phase fractions within the wires as the effective anisotropy significantly differs from the expected shape anisotropy for nanowires with high aspect ratio. This change in effective anisotropy is attributed to the preferential alignment of the c-axis of hcp Co-Pt phase perpendicular to the nanowires axis. A promising alternative with much smaller feature sizes is the diblock copolymer template. Electrodeposition of Co and Co-Pt into these templates has been carried out. Inhomogeneities in the template thickness as well as a certain substrate roughness have been identified to be the reasons for inhomogeneous template filling. Thus magnetic properties are dominated by large deposits found on top of the template. Additionally, rolled-up tubes of several nm thick Au/Co/Au films have been characterized magnetically. Temperature dependent measurements show an exchange bias behaviour that is explained in terms of induced stresses during cooling. Changes of magnetic properties in the investigated samples are finally discussed in terms of competing effects of different magnetic anisotropies in various geometries.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Technische Universität Dresden

Year

2010

Author dc:creator

• Khatri, Manvendra Singh

Contributors dc:contributor

• Schultz, L.
• Srinivas, V.

• magnetism
• thin films
• nanowires
• rolled-up tubes
• Magnetismus
• Dünnschichten
• Nanodrähte