• Callori, Sara J.
• Khaydukov, Yury
• James, Michael
• Klose, Frank
• Bertinshaw, Joel
• Brun, Anton P. Le
• Evans, Peter J.
• Aughterson, Robert
• Hughes, Jacob S.
• Sprouster, David J.
• Wang, Xiaolin L.
• Cortie, David L.
• Keller, Thomas
• Triani, Gerry

Abstract

<p>High magnetizations are desirable for spintronic devices that operate by manipulating electronic states using built-in magnetic fields. However, the magnetic moment in promising dilute magnetic oxide nanocomposites is very low, typically corresponding to only fractions of a Bohr magneton for each dopant atom. In this study, we report a large magnetization formed by ion implantation of Co into amorphous TiO_2-δ films, producing an inhomogeneous magnetic moment, with certain regions producing over 2.5 μ_B per Co, depending on the local dopant concentration. Polarized neutron reflectometry was used to depth-profile the magnetization in the Co:TiO_2-δ nanocomposites, thus confirming the pivotal role of the cobalt dopant profile inside the titania layer. X-ray photoemission spectra demonstrate the dominant electronic state of the implanted species is Co⁰, with a minor fraction of Co²⁺. The detected magnetizations have seldom been reported before and lie near the upper limit set by Hund's rules for Co⁰, which is unusual because the transition metal's magnetic moment is usually reduced in a symmetric 3D crystal-field environment. Low-energy positron annihilation lifetime spectroscopy indicates that defect structures within the titania layer are strongly modified by the implanted Co. We propose that a clustering motif is promoted by the affinity of the positively charged implanted species to occupy microvoids native to the amorphous host. This provides a seed for subsequent doping and nucleation of nanoclusters within an unusual local environment.</p>

Topics

• nanocomposite
• impedance spectroscopy
• cluster
• amorphous
• positron annihilation lifetime spectroscopy
• defect
• cobalt
• magnetization
• clustering
• defect structure
• reflectometry