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Title: The Verwey transition in nanostructured magnetite produced by a combination of chimie douce and spark plasma sintering

Magnetite nanoparticles about 10 nm sized were synthesized by the polyol method. Zero-field-cooled (ZFC)-FC measurements showed a blocking temperature ∼170 K and the absence of the Verwey transition. They were subsequently consolidated by spark plasma sintering at 750 °C for 15 min, leading to a high density (92% of the theoretical density), solid body, with grains in the 150 nm range. X-ray diffraction patterns exhibited a spinel single phase with cell parameters corresponding to the magnetite structure. Magnetic measurements showed a decrease of coercivity from 685 Oe (54.5 kA/m) at 118 K to 90 Oe (7.2 kA/m) at 139 K. ZFC measurements at 25 Oe presented a three-fold magnetization increase as temperature increased; a small transition between 116 and 117.5 K, followed by a larger one from 117.6 to 124 K. The first transition can be associated with a complex crystallographic transition and delocalization of Fe{sup 2+}-Fe{sup 3+}, while the second one can be attributed to spin reorientation due to the magnetocrystalline anisotropy constant (K{sub 1}) change of sign as previously observed only in magnetite single crystals.
Authors:
; ;  [1] ; ;  [2] ; ;  [3] ;  [4]
  1. ITODYS, Université Paris Diderot, PRES Sorbonne Paris Cité, CNRS-UMR 7086, 75205 Paris Cedex (France)
  2. Depto Materiales Metálicos y Cerámicos, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Mexico 04510 (Mexico)
  3. International Iberian Nanotechnology Laboratory, 4715-310 Braga (Portugal)
  4. SATIE, ENS Cachan, CNRS, UniverSud, F-94230 Cachan (France)
Publication Date:
OSTI Identifier:
22273883
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 17; Conference: 55. annual conference on magnetism and magnetic materials, Atlanta, GA (United States), 14-18 Nov 2010; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANISOTROPY; COERCIVE FORCE; DENSITY; IRON IONS; MAGNETITE; MAGNETIZATION; MONOCRYSTALS; NANOSTRUCTURES; PARTICLE SIZE; PARTICLES; PLASMA; SINTERING; SPIN; TEMPERATURE DEPENDENCE; X-RAY DIFFRACTION