Unveiling a New High-Temperature Ordered Magnetic Phase in ϵ-Fe2O3
García-Muñoz, José Luis (Institut de Ciència de Materials de Barcelona)
Romaguera, Arnau (Institut de Ciència de Materials de Barcelona)
Fauth, François (ALBA Laboratori de Llum de Sincrotró)
Nogués, Josep (Institut Català de Nanociència i Nanotecnologia)
Gich García, Martí (Institut de Ciència de Materials de Barcelona)

Data:	2017
Resum:	Iron oxides are among the most abundant materials on Earth, and yet there are some of their basic properties which are still not well-established. Here, we present temperature-dependent magnetic, X-ray, and neutron diffraction measurements refuting the current belief that the magnetic ordering temperature of ϵ-FeO is ∼500 K, i. e. , well below that of other iron oxides such as hematite, magnetite, or maghemite. Upon heating from room temperature, the ϵ-FeO nanoparticles' saturation magnetization undergoes a monotonic decrease while the coercivity and remanence sharply drop, virtually vanishing around ∼500 K. However, above that temperature the hysteresis loops present a nonlinear response with finite coercivity, making evident signs of ferrimagnetic order up to temperatures as high as 850 K (T). The neutron diffraction study confirms the presence of ferrimagnetic order well above 500 K with Pna'2' magnetic symmetry, but only involving two of the four Fe sublattices which are ordered below T ≈ 480 K, and with a reduced net ferromagnetic component, that vanishes at above 850 K. The results unambiguously show the presence of a high-temperature magnetic phase in ϵ-FeO with a critical temperature of T ∼ 850 K. Importantly, this temperature is similar to the Curie point in other iron oxides, indicating comparable magnetic coupling strengths. The presence of diverse magnetic phases is further supported by the nonmonotonic evolution of the thermal expansion. The existence of a high-temperature ferrimagnetic phase in ϵ-FeO may open the door to further expand the working range of this multifunctional iron oxide.
Ajuts:	Ministerio de Economía y Competitividad MAT2015-686760-02-2-P Ministerio de Economía y Competitividad MAT2012-38213-C02-02 Ministerio de Economía y Competitividad MAT2016-77391-R Ministerio de Economía y Competitividad SEV-2015-0496 Ministerio de Economía y Competitividad SEV-2013-0295 Agència de Gestió d'Ajuts Universitaris i de Recerca 2014/SGR-213 Agència de Gestió d'Ajuts Universitaris i de Recerca 2014/SGR-1015
Drets:	Tots els drets reservats.
Llengua:	Anglès
Document:	Article ; recerca ; Versió sotmesa a revisió
Matèria:	Coercivity and remanences ; Critical temperatures ; Ferrimagnetic order ; Ferromagnetic component ; Magnetic ordering temperatures ; Neutron diffraction measurements ; Neutron diffraction studies ; Temperature dependent
Publicat a:	Chemistry of materials, Vol. 29, Issue 22 (November 2017) , p. 9705-9713, ISSN 1520-5002

DOI: 10.1021/acs.chemmater.7b03417

Preprint 21 p, 1.9 MB

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