Synthesis and Magnetic Properties of Gd Doped EuS Nanocrystals with Enhanced Curie Temperatures

EuS nanocrystals (NCs) were doped with Gd resulting in an enhancement of their magnetic properties. New EuS and GdS single source precursors (SSPs) were synthesized, characterized, and employed to synthesize Eu1−xGdxS NCs by decomposition in oleylamine and trioctylphosphine at 290 °C. The doped NCs were characterized using X-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy, which support the uniform distribution of Gd dopants through electron energy loss spectroscopy (EELS) mapping. X-ray absorption spectroscopy (XAS) revealed the dopant ions in Eu1−xGdxS NCs to be predominantly Gd3+. NCs with a variety of doping ratios of Gd (0 ≤ x < 1) were systematically studied using vibrating sample magnetometry and the observed magnetic properties were correlated with the Gd doping levels (x) as quantified with ICP-AES. Enhancement of the Curie temperature (TC) was observed for samples with low Gd concentrations (x ≤ 10%) with a maximum TC of 29.4 K observed for NCs containing 5.3% Gd. Overall, the observed TC, Weiss temperature (θ), and hysteretic behavior correspond directly to the doping level in Eu1−xGdxS NCs and the trends qualitatively follow those previously reported for bulk and thin film samples.