Wednesday, 11 March 2015

FM at the interface of AF Co oxide NanoOctahedra NP, Room T magnetism and EB

Electrostatic doping as a source for robust ferromagnetism at the interface between antiferromagnetic cobalt oxides.
Zi-An Li, N. Fontaíña-Troitiño, A. Kovács, S. Liébana-Viñas, M. Spasova, R. E. Dunin-Borkowski, M. Müller, D. Doennig, R. Pentcheva, M. Farle & V. Salgueiriño 
(a) Size dependence of experimentally measured (black solid (T = 5 K) and dashed (300 K) lines) and calculated saturation magnetization MS of CoO octahedra. A magnetic moment μ of (4.8 ± 0.4)μB per Co2+ ion and a shell thickness of 3 nm Co3O4 is assumed. MS arises only from the Co cations at the surfaces or interfaces of the octahedral nanocrystals, as indicated in the schematic in (b). The blue lines are calculated values assuming only effectively one layer of Co2+ cations at the Co3O4 surface, while the red lines correspond to a double layer of Co cations at the interface.
Room-Temperature Ferromagnetism in Antiferromagnetic Cobalt Oxide Nanooctahedra.  
N. Fontaíña-Troitiño, S. Liébana-Viñas, Benito Rodríguez-González, Zi-An Li, M. Spasova, M. Farle, V. Salgueiriño
Nano Lett..14, 640 (2014)
Cobalt oxide octahedra were synthesized by thermal decomposition. Each octahedron-shaped nanoparticle consists of an antiferromagnetic CoO core enclosed by eight {111} facets interfaced to a thin (∼4 nm) surface layer of strained Co3O4. The nearly perfectly octahedral shaped particles with 20, 40, and 85 nm edge length show a weak room-temperature ferromagnetism that can be attributed to ferromagnetic correlations appearing due to strained lattice configurations at the CoO/Co3O4 interface.

Exchange Bias Effect in CoO@Fe3O4 Core−Shell Octahedron-Shaped Nanoparticles.  
Nerio Fontaíña Troitiño, Beatriz Rivas-Murias, Benito Rodríguez-González, and Verónica Salgueiriño
Chem. Mater. 26, 5566 (2014)
Increased coercive and tunable exchange bias field values were registered in hybrid CoO@Fe3O4 core–shell octahedron-shaped nanoparticles of different average size. In this strained morphology, the metal cation chemical potentials at the interface between the antiferromagnetic and ferrimagnetic oxides become a very dynamic variable. This causes the effective magnetic anisotropy to increase and the type of interface to change after growing the magnetite shell epitaxially onto the cobalt oxide {111} surface facets and, consequently, to tune the exchange bias effect.

 

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