Superantiferromagnetic EuTe nanoparticles: room temperature colloidal synthesis, structural characterization, and magnetic properties† Weidong He, ad Suseela Somarajan, bd Dmitry S. Koktysh cd and James H. Dickerson * bd Received 25th August 2010, Accepted 11th October 2010 DOI: 10.1039/c0nr00625d In this communication, EuTe nanoparticles with different size distributions have been synthesized for the first time at room temperature by injection of ethylene glycol solution of Na 2 Te into ethylene glycol solution of EuCl 2 in the presence of triethanolamine. By adding phenanthroline into EuCl 2 solution, EuTe nanospindles have also been synthesized. The as-synthesized EuTe nanocrystals show size-dependent optical properties. Low-temperature magnetic measurements show that 6.5 nm EuTe nanoparticles show pronounced superantiferromagnetic transition between 2 K and 20 K. Our facile synthesis route opens up the opportunity of studying and applying this classical Heisenberg antiferromagnetic material in quantized-size range; our magnetic analysis indicates that the properties of EuTe can be tuned by the change of its diameter. Both the spin configuration and the 4f–5d electronic transition of europium(II) chalcogenides (EuX: X ¼ O, S, Se, Te) make these materials promising candidates for advanced magnetic, optical, and electronic applications. 1–6 Among the europium chalcogenides, EuTe is a classical Heisenberg antiferromagnetic material with a N eel temperature of 9.6 K and a NaCl structure. 7–9 Interest in synthesizing nanoscale EuX has continued to grow considerably during the past decade. For example, colloidal EuO, EuS and EuSe nanoparticles (NPs) have been synthesized by a variety of groups. 10–16 However, there has been no report on the synthesis of EuTe nanoparticles, which are as intriguing as the other EuX NPs regarding synthetic chemistry, optical and magnetic properties. In this communication, we report the first colloidal synthesis of EuTe nanostructures, using ethylene glycol (EG) as solvent and triethanolamine (TEA) as stabilizer, and the observation of nanocrystalline boundary effects on the magnetic response of these materials. EuTe NPs were synthesized by the injection of a solution of Na 2 Te into a well stirred EG plus TEA solution of EuCl 2 . Reductive TEA and EG keep both Eu 2+ and Te 2 from oxidation while TEA metal chelate formed in this proce- dure balances nucleation and growth steps in the synthesis. The synthesis renders a fast growth mechanism as well as a narrow size distribution of the EuTe NPs at room temperature. EuTe NPs of different sizes were synthesized by setting the concentrations of the EuCl 2 and Na 2 Te. By introducing phenanthroline along with TEA under the same conditions, EuTe nanospindles (NSs) were also achieved. In addition, the magnetic properties of EuTe NPs were measured and analyzed. All synthetic steps were carried out in nitrogen filled, moisture free glove box at room temperature. In the synthesis of 6.5 nm EuTe NPs, EuCl 2 (0.0446 g) was dissolved in a mixture solution of 15 mL ethylene glycol (EG) and 4 mL triethanolamine (TEA) under vigorous stirring. 2 mL of 0.1 M solution of Na 2 Te in EG were added dropwise into the vigorously stirred EuCl 2 solution. The resulting black-colored EuTe nanoparticles were separated out via centrifu- gation, washed repeatedly with methanol, and finally stored in methanol for further measurements. The synthesis of 7.3 nm and 5.5 nm EuTe NPs is the same as that for 6.5 nm EuTe nanoparticles except that the concentrations of EuCl 2 and Na 2 Te were 0.1 M and 0.4 M, respectively. In typical synthesis of EuTe NSs, 0.036 g phe- nanthroline was dissolved in 2 mL EG and injected into EuCl 2 /EG solution before the injection of Na 2 Te/EG solution. Other parts of the synthetic procedure followed that of the 6.5 nm EuTe NPs synthesis. High resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) pattern images were obtained using a Philips CM20 TEM operating at 200 kV. HR-TEM samples were made by drop-casting the EuTe nanoparticle suspen- sions on carbon-coated copper grids. The UV-Vis spectra were recorded with a Varian Cary 5000 UV-VIS-NIR spectrophotometer. Powder XRD measurements were made using a Scintag X1 powder diffractometer. A Bruker Tensor 27 FTIR spectrometer was used to measure FTIR spectra of EuTe NPs. Energy dispersive X-ray (EDS) analysis was performed using a Hitachi S-4200 Scanning Electron Microscope operated at 20 kV acceleration voltage. The ease of TEA bonding to Eu 2+ ions in the EG solution facili- tated the formation of a chelate compound [Eu(TEA) n ]Cl 2 in the early stages of the synthesis. 17 Upon injection of the EG solution of Na 2 Te, EuTe NPs were formed, which readily precipitated in the reactor. Two reaction steps are associated with the formation of EuTe, as described in Scheme 1, which is consistent with the report from Xu et al. on SnS. 18 Synthesized EuTe NPs were capped by groups of TEA, which was confirmed by Fourier transform infrared spectroscopy (FTIR), shown in Fig. S1† (in the ESI). The ligands largely helped prevent EuTe oxidation in an oxygen present envi- ronment. Typical transmission electron microscope (TEM) images of EuTe NPs are shown in Fig. 1(a). As seen from the images, the NPs were Scheme 1 Reaction schematic of EuTe colloidal synthesis. a Interdisciplinary Graduate Program in Materials Science, Vanderbilt University, Nashville, TN, USA b Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA c Department of Chemistry, Vanderbilt University, Nashville, TN, USA d Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, TN, USA. E-mail: james.h.dickerson@vanderbilt. edu; Fax: +1-615-343-1708; Tel: +1-615-343-2957 † Electronic supplementary information (ESI) available: Fig. S-1 through S-5. See DOI: 10.1039/c0nr00625d This journal is ª The Royal Society of Chemistry 2010 Nanoscale COMMUNICATION www.rsc.org/nanoscale | Nanoscale Downloaded on 19 November 2010 Published on 01 November 2010 on http://pubs.rsc.org | doi:10.1039/C0NR00625D View Online