| AVS 56th International Symposium & Exhibition | |
| Magnetic Interfaces and Nanostructures | Thursday Sessions |
| Session MI+TF-ThA |
| Session: | Magnetic Thin Films: Multilayers and Nanostructures |
| Presenter: | J.R.I. Lee, Lawrence Livermore National Laboratory |
| Authors: | J.R.I. Lee, Lawrence Livermore National Laboratory R.W. Meulenberg, University of Maine S.K. McCall, Lawrence Livermore National Laboratory K.M. Hanif, Naval Research Laboratory J.C. Lang, Argonne National Laboratory D. Haskel, Argonne National Laboratory L.J. Terminello, Lawrence Livermore National Laboratory T. van Buuren, Lawrence Livermore National Laboratory |
| Correspondent: | Click to Email |
The observation of magnetism has recently been reported for numerous nanoscale materials that do not demonstrate comparable behavior in bulk form. This is intriguing because coupling the magnetic properties of the nanocrystalline materials with their size-dependent optical and electronic behavior presents the potential for application in a variety of technologies. Identifying the origin of the magnetic properties is, therefore, of paramount importance. To date, several conflicting mechanisms have been proposed in studies of a number of nanoscale systems and, significantly, the cause of the magnetism remains a matter of some controversy in the literature. For example, the ferromagnetic behavior observed for Au nanocrystals (NCs) has been attributed to interactions with the organic surface passivant in one study and an intrinsic property of the nanoscale metal in another. Comparable sources have been also been proposed for the magnetic properties of CdSe NCs, along with an alternative possibility that defect sites are responsible. We report a systematic investigation of the effects of the surface passivant on CdSe NCs using a combination of x-ray magnetic circular dichroism (XMCD) spectroscopy, superconducting quantum interference device (SQUID) magnetometry and x-ray absorption spectroscopy (XAS). The suite of experiments demonstrates that, contrary to the findings of prior studies, our NCs are not ferromagnetic and instead exhibit paramagnetic behavior. In addition, the magnetic susceptibility is dependent on interactions with the organic molecule used to passivate the surface of the CdSe NCs. More specifically, the paramagnetic properties depend upon electron transfer at the molecular level via π-back donation between surface Cd atoms and the organic ligands.
Project 07-LW-041 was funded by the LDRD Program at LLNL. This work was partially supported by the OBES, DMR, under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. Use of the ALS and APS was supported by the U.S. DOE, Office of Science, OBES, under Contracts DE-AC02-05CH11231 and DE-AC02-06CH11357, respectively.