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Title: Size effects in the magnetic properties of ε-Fe{sub 2}O{sub 3} nanoparticles

We report the results of comparative analysis of magnetic properties of the systems based on ε-Fe{sub 2}O{sub 3}, nanoparticles with different average sizes (from ∼3 to 9 nm) and dispersions. The experimental data for nanoparticles higher than 6–8 nm in size are consistent with the available data, specifically, the transition to the magnetically ordered state occurs at a temperature of ∼500 K and the anomalies of magnetic properties observed in the range of 80–150 K correspond to the magnetic transition. At the same time, Mőssbauer and ferromagnetic resonance spectroscopy data as well as the results of static magnetic measurements show that at room temperature all the investigated samples contain ε-Fe{sub 2}O{sub 3} particles that exhibit the superparamagnetic behavior. It was established that the magnetic properties of nanoparticles significantly change with a decrease in their size to ∼6 nm. According to high-resolution electron microscopy and Mőssbauer spectroscopy data, the particle structure can be attributed to the ε–modification of trivalent iron oxide; meanwhile, the temperature of the magnetic order onset in these particles is increased, the well-known magnetic transition in the range of 80–150 K does not occur, the crystallographic magnetic anisotropy constant is significantly reduced, and the surface magnetic anisotropy plays a decisive role. This is apparentlymore » due to redistribution of cations over crystallographic positions with decreasing particle size, which was established using Mössbauer spectra. As the particle size is decreased and the fraction of surface atoms is increased, the contribution of an additional magnetic subsystem formed in a shell of particles smaller than ∼4 nm becomes significant, which manifests itself in the static magnetic measurements as paramagnetic contribution.« less
Authors:
 [1] ;  [2] ;  [1] ;  [3] ; ; ;  [1] ; ;  [4] ;  [3] ;  [4]
  1. Kirensky Institute of Physics, Krasnoyarsk 660036 (Russian Federation)
  2. (Poland)
  3. (Russian Federation)
  4. Boreskov Institute of Catalysis, Novosibirsk 630090 (Russian Federation)
Publication Date:
OSTI Identifier:
22492995
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 21; Other Information: (c) 2015 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; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANISOTROPY; CATIONS; CRYSTALLOGRAPHY; ELECTRON MICROSCOPY; EXPERIMENTAL DATA; FERROMAGNETIC RESONANCE; IRON OXIDES; MAGNETIC PROPERTIES; MOESSBAUER SPECTROMETERS; NANOPARTICLES; PARAMAGNETISM; PARTICLE SIZE; PARTICLE STRUCTURE; SUPERPARAMAGNETISM; SURFACES; TEMPERATURE RANGE 0273-0400 K