Role of the oxygen partial pressure in the formation of composite Co-CoO nanoparticles by reactive aggregation

• Published in: Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology Vol. 13; no. 10; pp. 4583 - 4590
• Main Authors: De Toro, J. A., Andrés, J. P., González, J. A., Riveiro, J. M., Estrader, M., López–Ortega, A., Tsiaoussis, I., Frangis, N., Nogués, J.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.10.2011; Springer Nature B.V
• Subjects: Agglomeration; Characterization and Evaluation of Materials; Chemistry and Materials Science; Cobalt; Exchange; Inorganic Chemistry; Lasers; Magnetic properties; Materials Science; Nanocomposites; Nanomaterials; Nanoparticles; Nanostructure; Nanotechnology; Optical Devices; Optics; Partial pressure; Photonics; Physical Chemistry; Research Paper; Nanocomposite; Cluster source; Magnetic nanoparticles; Exchange bias
• ISSN: 1388-0764; 1572-896X
• DOI: 10.1007/s11051-011-0418-8

The magnetic properties of diluted films composed of nanocomposite Co-CoO nanoparticles (of ~8 nm diameter) dispersed in a Cu matrix have been investigated. The nanoparticles were formed in an aggregation chamber by sputtering at different Ar/O 2 partial pressures (0–0.015). The exchange-bias properties appear to be insensitive to the amount of O 2 during their formation. However, the temperature dependence of the magnetization, M(T), exhibits two different contributions with relative intensities that correlate with the amount of O 2 . The magnetic results imply that two types of particles are formed, nanocomposite Co-CoO (determining the exchange-bias) and pure CoO, as confirmed by transmission electron microscopy observations. Importantly, as the O 2 partial pressure during the sputtering is raised the number of nanocomposite Co-CoO nanoparticles (exhibiting exchange-bias properties) is reduced and, consequently, there is an increase in the relative amount of pure, antiferromagnetic CoO particles.