Design and Functionalization of Magnetic Core-Shell Oxide Nanoparticles Exhibiting Exchange Bias Features
- PDF / 334,396 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 51 Downloads / 179 Views
Design and Functionalization of Magnetic Core-Shell Oxide Nanoparticles Exhibiting Exchange Bias Features Fayna Mammeri1, Faïza Mamèche1, Zeinab Kataya2, Nader Yaacoub2, Anna SlawskaWaniewska3, Nicolas Menguy4, Jean-Marc Grenèche2 and Souad Ammar1 1 ITODYS, Univ Paris-Diderot, Sorbonne Paris Cité, UMR 7086 CNRS, 15 Rue Jean-Antoine de Baïf, Paris, 75205 France. 2 LPEC, Univ du Maine, UMR 6087 CNRS, Avenue Olivier Messiaen, Le Mans, 72085 France 3 IFPAN, al. Lotników 32/46, Warszaw, 02-668 Poland 4 IMPMC, Univ Paris 6, Paris Sorbonne, UMR 7590 CNRS, 4 Place Jussieu, Paris, 75005 France ABSTRACT Core-shell magnetic nanoparticles (CSNPs) composed of a ferrimagnetic core (CoFe2O4) embedded in an antiferromagnetic shell (CoO) were produced using seed mediated growth in a polyol. Different core sizes and shell thicknesses were considered. The structural and magnetic properties of assemblies of these nanoparticles were characterized by means of X-ray Diffraction, Transmission Electron Microscopy, dc-magnetometry (SQUID) and 57Fe Mössbauer spectrometry. The measured EB magnetic field values, at low temperature, are found to be weak whatever the microstructural characteristics of the studied CSMNPs. Simultaneously, both the magnetization and the interparticle interaction (mainly dipolar) appear clearly reduced when the shell thickness increases. INTRODUCTION Tailoring the size of the magnetic particles at the nanometer scale has led to the emergence of new magnetic properties, of great interest in various research topics ranging from magnetic recording and quantum computing to earth science and biomedicine. Nanomaterials display peculiar magnetic properties that are not present in their bulk counterparts and due to the synergy between intrinsic properties, arising from finite size effect, and collective effects induced by the different kinds of interparticles or intercrystals interactions. The thermal stability of the nanomaterials magnetization is one of the key issues for most applications and is particularly critical for magnetic recording. Several recent experimental studies have indicated that exchange coupled ferromagnetic (FM) and antiferromagnetic (AFM) nanostructures exhibit an improved thermal stability of the magnetization, in agreement with theoretical models.1,2 The studied nanostructures exhibit all the features of exchange bias (EB) due to the exchange coupling between the spins at the interface between the FM core and the surrounding AFM shell. Experimentally, EB is demonstrated by a hysteresis loop shift along the field axis and a coercivity enhancement when the material is cooled from a starting temperature ranged between TN (Néel temperature) and TC (Curie temperature) in the presence of an applied magnetic field. Such an additional and unidirectional anisotropy would be a good opportunity to increase the thermal transition from the blocked FM state to the superparamagnetic one up to room temperature. The use of such core-shell nanoparticles (CSNPs) in magnetic devices is depending on their ability to be p
Data Loading...
