Electric and magnetic properties of Eu<inf>1-x</inf>Gd<inf>x</inf>S films and GdS-EuS film junctions

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

“…Positive Weiss constant values indicate that a material is ferromagnetic and negative values indicate antiferromagnetism. As seen in Figure 9b, for samples with low Gd concentrations, the Weiss constant is both positive and enhanced as compared to undoped EuS, consistent with bulk values41 where the literature values are represented by crosses and our experimental values are represented by circles. As the concentration of Gd increases, the Weiss constant decreases, eventually becoming negative indicating the transition to antiferromagnetism 39,65–67.…”

“…This clearly shows the most significant T C enhancement occurs over the range 2.6 – 5.3 % Gd with the highest T C at 29.4 K. This is slightly greater than the concentration regime of highest T C enhancement reported for bulk Eu 1- x Gd x S (1 – 3 % Gd) 39. The overall behavior qualitatively follows the theoretical model of the RKKY coupling mechanism where localized spins are coupled through conduction electrons 14,38–41. Just as seen experimentally, Gd 3+ ions provide the same local moments as Eu 2+ and add electron density to the conduction band, which in turn improves the magnetic coupling, therefore enhancing the T C 40.…”

“…A more refined synthesis of EuS NCs provides the foundation for designing an effective method for synthesizing Eu 1- x Gd x S NCs. Bulk crystals and thin films of Gd doped EuS have been prepared through co-melting, electron-beam deposition, and flash evaporation (methods incompatible with all existing EuS NC synthetic schemes) and have been shown to have enhanced T C up to 50 K 39,41…”

“…Although methods for preparing bulk Eu 1- x Gd x S have been developed including co-melting and cooling of EuS and GdS ingots, electron-beam deposition, and flash evaporation,39,41 Gd doping of EuS NCs has not been previously reported. Pure EuS NCs can be synthesized using a variety of methods including growth from liquid ammonia,42,43 white light44 and microwave irradiation,45 zeolite templating,46 and decomposition of single source precursors 47,48.…”

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.…”