Exchange bias and surface effects in bimagnetic CoO-core/Co0.5Ni0.5Fe2 O4 -shell nanoparticles
Bimagnetic nanoparticles have been proposed for the design of new materials with controlled properties, which requires a comprehensive investigation of their magnetic behavior due to multiple effects arising from their complex structure. In this work we fabricated bimagnetic core/shell nanoparticles...
| Autores: | , , , , , , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2016 |
| País: | Argentina |
| Institución: | Consejo Nacional de Investigaciones Científicas y Técnicas |
| Repositorio: | CONICET Digital (CONICET) |
| Idioma: | inglés |
| OAI Identifier: | oai:ri.conicet.gov.ar:11336/126149 |
| Acceso en línea: | http://hdl.handle.net/11336/126149 |
| Access Level: | acceso abierto |
| Palabra clave: | CORE/SHELL NANOPARTICLES EXCHANGE-BIAS MAGNETIC NANOPARTICLES FERRITES https://purl.org/becyt/ford/2.10 https://purl.org/becyt/ford/2 https://purl.org/becyt/ford/1.3 https://purl.org/becyt/ford/1 |
| Sumario: | Bimagnetic nanoparticles have been proposed for the design of new materials with controlled properties, which requires a comprehensive investigation of their magnetic behavior due to multiple effects arising from their complex structure. In this work we fabricated bimagnetic core/shell nanoparticles formed by an ∼3-nm antiferromagnetic (AFM) CoO core encapsulated within an ∼1.5-nm ferrimagnetic (FiM) Co0.5Ni0.5Fe2O4 shell, aiming at studying the enhancement of the magnetic anisotropy and the surface effects of a ferrimagnetic oxide shell. The magnetic properties of as-synthesized and annealed samples were analyzed by ac and dc magnetization measurements. The results indicate that the magnetic response of the as-synthesized particles is governed by the superparamagnetic behavior of the interacting nanoaggregates of spins that constitute the disordered ferrimagnetic shell, whose total moments block at (TB)=49 K and collectively freeze in a superspin-glass-type state at (Tg)=3 K. On the other hand, annealed nanoparticles are superparamagnetic at room temperature and behave as an exchange-coupled system below the blocking temperature (TB)=70 K, with enhanced coercivity HC(10K)∼14.6 kOe and exchange bias field HEB(10K)∼2.3 kOe, compared with the as-synthesized system where HC(10K)∼5.5 kOe and HEB(10K)∼0.8 kOe. Our results, interpreted using different models for thermally activated and surface relaxation processes, can help clarify the complex magnetic behavior of many core/shell and hollow nanoparticle systems. |
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