High magnetization materials are in great demand for the fabrication of advanced multifunctional magnetic devices. Notwithstanding this demand, the development of new materials with these attributes has been relatively slow. In this work, we propose a new strategy to achieve high magnetic moments above room temperature. Our material engineering approach invoked the embedding of magnetic nanoclusters in an oxide matrix. By precisely controlling pulsed laser deposition parameters, Co nanoclusters are formed in a 5 at % Co-TiO2 film. The presence of these nanoclusters was confirmed using transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray absorption fine structure. The film exhibits a very high saturation magnetization of 99 emu/cm3. Detailed studies using X-ray magnetic circular dichroism confirm that Co has an enhanced magnetic moment of 3.5 μB/atom, while the Ti and O also contribute to the magnetic moments. First-principles calculations supported our hypothesis that the metallic Co nanoclusters surrounded by a TiO2 matrix can exhibit both large spin and orbital moments. Moreover, a quantum confinement effect results in a high Curie temperature for the embedded Co nanoclusters. These findings reveal that 1-2 nm nanoclusters that are quantum confined can exhibit very large magnetic moments above room temperature, representing a promising advance for the design of new high magnetization materials.
|Original language||English (US)|
|Number of pages||8|
|Journal||ACS Applied Materials and Interfaces|
|State||Published - Oct 29 2019|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The PNR research conducted at ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division,
Office of Basic Energy Sciences, and US Department of Energy. J.B.Y. would like to thank the research support for Australian Research Council (ARC) Future Fellowship (FT160100205). S.P.R. and R.Z. acknowledge support from the ARC (DP150100018). The authors acknowledge gratefully the scientific and technical support provided by the Microscopy Australia node at the University of Sydney (Sydney Microscopy & Microanalysis). J.B.Y. and X.D. would like to acknowledge gratefully the Australian National Fabrication Facility (ANFF) node at UNSW for technical support and access to the LaserMBE system. Prof. Jianhua Zhao is thanked for advice and support in relation to the SQUID measurements. Our calculations were undertaken with the assistance of resources from the National Computational Infrastructure (NCI) and the authors acknowledge the high-performance computing support from the Sydney Informatics Hub at the University of Sydney for expert facilitation of our access to the NCI. ANFF, Microscopy Australia, and the NCI are supported by the Australian Government under the National Collaborative Research Infrastructure Scheme (NCRIS) program.