Growth, structure and magnetism of ϵ-Fe2O3 in nanoparticle form

We present a novel and easy synthetic path to prepare ϵ-FeO (∼90%) with a small portion of α-FeO nanoparticles embedded in an amorphous silica matrix. An exhaustive structural study reveals the higher relative concentration of the ϵ-phase, with an average particle size of 17 nm. Confocal Raman microscopy and X-ray absorption spectroscopy are presented as novel techniques to characterize the ϵ-polymorph. The magnetic properties have been studied in a wide range of temperatures (5-1000 K), detecting blocking effects (∼135 K), collapse effects (50-125 K), Morin (∼268 K) and Néel (∼505 K) transitions.This work has been supported by the Ministerio Español de Economía y Competitividad (MINECO) through the projects MAT2012-38045-C04-03, MAT2012-38045-C04-01-P, MAT2013-48009-C04-01-P and FIS-2008-06249. J. L.-S. and M. A. thank the FPI fellowship and the UCM Campus of International Excellence (PICATA Program), respectively. Dr A. del Campo is acknowledged for the assistance with the CRM measurements.Peer Reviewe