Structural and Magnetic Properties of CoO-Pt core-shell nanoparticles
| Autor: | Zelenakova, Adriana, Zelenak, Vladimir, Michalik, Stefan, Kovac, Jozef, Meisel, Mark W. |
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| Rok vydání: | 2013 |
| Předmět: | |
| Zdroj: | Phys. Rev. B 89, 104417 (2014) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevB.89.104417 |
| Popis: | Using microemulsion methods, CoO-Pt core-shell nanoparticles (NPs), with diameters of nominally 4 nm, were synthesized and characterized by high-resolution transmission electron microscopy (HRTEM) and a suite of x-ray spectroscopies, including diffraction (XRD), absorption (XAS), absorption near-edge structure (XANES), and extended absorption fine structure (EXAFS), which confirmed the existence of CoO cores and pure Pt surface layers. Using a commercial magnetometer, the ac and dc magnetic properties were investigated over a range of temperature (2 K $\leq$ T $\leq$ 300 K), magnetic field ($\leq$ 50 kOe), and frequency ($\leq$ 1 kHz). The data indicate the presence of two different magnetic regimes whose onsets are identified by two maxima in the magnetic signals, with a narrow maximum centered at 6 K and a large one centered at 37 K. The magnetic responses in these two regimes exhibit different frequency dependences, where the maximum at high temperature follows a Vogel-Fulcher law, indicating a superparamagnetic (SPM) blocking of interacting nanoparticle moments and the maximum at low temperature possesses a power law response characteristic of a collective freezing of the nanoparticle moments in a superspin glass (SSG) state. This co-existence of blocking and freezing behaviors is consistent with the nanoparticles possessing an antiferromagnetically ordered core, with an uncompensated magnetic moment, and a magnetically disordered interlayer between CoO core and Pt shell. Comment: 11 pages, 11 figures |
| Databáze: | arXiv |
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