Strongly exchange coupled inverse ferrimagnetic soft|hard, MnxFe3-xO4|FexMn3-xO4, core|shell heterostructured nanoparticles

http://pubs.rsc.org/en/content/articlelanding/2012/nr/c2nr30986f

Nanoscale, 2012,4, 5138-5147

Marta Estrader ,  Alberto López-Ortega ,  German Salazar-Alvarez,  Igor Golosovsky ,  Marianna Vasilakaki ,  Kalliopi Trohidou , David Keavney ,  Randy Dumas ,  Jordi Sort ,  Sonia Estrade , Dolors Baro ,  Santiago Suriñach ,  Francesca Peiro and Josep Nogués

Inverted soft|hard, in contrast to conventional hard|soft, bi-magnetic core|shell nanoparticles of Mn_xFe_3-xO₄|Fe_xMn_3-xO₄ with two different core sizes (7.5 and 11.5 nm) and fixed shell thickness (~ 0.6 nm) have been synthesized. The structural characterization suggests that the particles have an interface with a graded composition. The magnetic characterization confirms the inverted soft|hard structure and evidences a strong exchange coupling between the core and the shell. Moreover, larger soft core sizes exhibit smaller coercivities and loop shifts, but larger blocking temperatures, as expected from spring-magnet or graded anisotropy structures. The results indicate that, similar to thin film systems, the magnetic properties of soft|hard core|shell nanoparticles can be fine tuned to match specific applications.

Cold Consolidation of Metal–Ceramic Nanocomposite Powders with Large Ceramic Fractions

http://onlinelibrary.wiley.com/doi/10.1002/adfm.200800456/abstract

Advanced Functional Materials

Volume 18, Issue 20, pages 3293–3298, October 23, 2008

Enric Menéndez, German Salazar-Alvarez, Alexander P. Zhilyaev, Santiago Suriñach, Maria Dolors Baró, Josep Nogués, Jordi Sort

DOI: 10.1002/adfm.200800456

Abstract

Co/α-Al₂O₃ powder mixtures (5, 10, 20, 30, 40, and 50 mass % of α-Al₂O₃) have been ball-milled and, subsequently, consolidated at room temperature by means of a high pressure torsion procedure in order to produce bulk nanostructured composites. For mixtures up to 20% of α-Al₂O₃, the cold-compaction results in roughly fully dense disks with relatively high microhardness values. However, the compaction for 30, 40, and 50% of α-Al₂O₃ is less effective, resulting in a reduction of the microhardness although a structure in the nanoscale range is still preserved. A detailed structural investigation has been also performed.