Size-Dependent Magnetism of EuS Nanoparticles

Abstract

EuS nanoparticles were synthesized by solution-phase thermolysis of the diethylammonium salt of the anionic europium dithiocarbamate complex, [Eu(S 2 CNEt 2 ) 4 ] -. Oleylamine and triphenylphosphine were used as surfactants to prevent nanoparticle agglomeration and stabilize particle growth. By varying the synthetic parameters such as reaction temperature, heating time, and the [surfactant]:[precursor] ratio, nanoparticles of different sizes were obtained. The size-dependent magnetic properties of these nanoparticles were studied, and it was observed that a decrease in the ferromagnetic ordering temperature occurs with decreasing particle size.

Europium chalcogenide magnetic semiconductor nanostructures

“…What is clear from our data and the literature is that the large increase in magnetization occurs at decreasing temperatures, as a function of particle size [37]. Unfortunately, the evidence for size dependent band gap changes is quite weak.…”

“…For example, an increase of oleylamine and triphenyl phosphine rather than tri-octylphosphine allowed for a reduction in temperature while still producing crystalline nanoparticles. Oleylamine has previously been shown to reduce the decomposition temperature of the dithiocarbamate complexes [59]. Although many semiconductor nanoparticle syntheses use TOP, we found that the need to filter the solvent and the ease of oxidation made TOP less convenient to work with.…”

“…A related, alternative precursor to the neutral tris compound are salts of the tetrakis complex, Eu(S 2 CNR 2 ) 4 − . This precursor lacks phenanthroline or bpy, which can interfere with optical studies of the nanoparticles [37]; unfortunately these salts are less stable and more difficult to work with. The utility of Eu(S 2 CNR 2 ) 3 L was quickly recognized by several investigators and is used in most reports of EuS nanoparticles.…”

“…Crystallite size can also be determined indirectly, from calculations based on powder X-ray Reprinted with permission from Ref. [37]. Copyright 2008 American Chemical Society.…”

Element-specific magnetometry of EuS nanocrystals

“…ous reports that EuS NCs in the range of 10 nm will have depressed T C values due to surface and quantum effects. 14,16 Using the Curie-Weiss law the Weiss temperature was determined to be 15.7 K which is positive indicating ferromagnetic ordering and similar in magnitude to the reported value of 19 K. 17,18 The effective magnetic moment ͑ eff ͒ is 2.0 B , which is much lower than the 7.9 B expected for pure bulk EuS. As will be discussed in greater detail below, XAS showed there to be 30% of ferromagnetically ordered Eu 2+ and 70% of paramagnetically ordered Eu 3+ present.…”