Synthesis and characterisation of magnetic iron sulfide nanocrystals

Fe1-xS and Fe3S4 nanocrystals with a variety of morphologies and average sizes were synthesised by the reaction of iron(II) acetylacetonate (Fe(acac)(2)) and elemental sulfur in oleylamine. Reaction at 200 degrees C for 240 min produced extremely thin Fe3S4 sheets, which displayed low coercivities (14 kA m(-1)) suggestive of pseudosingle-domain or multidomain particles. Reaction temperatures >= 300 degrees C for 30 min produced 70 nm Fe1-xS nanocrystals with hexagonal plate and hexagonal prism morphologies, which displayed high magnetic coercivities (110 kA m(-1)) characteristic of single magnetic domain particles. Rapid injection of sulfur solution at 280 degrees C followed by immediate cooling produced a mixture of Fe1-xS nanocrystals and spherical, polydisperse similar to 5 nm Fe3S4 nanocrystals, which displayed superparamagnetism above an average blocking temperature of 55 K. (C) 2012 Elsevier Inc. All rights reserved.