### Session E3: Prussian Blue Analogs and Magnetite

Chair: Heinz Nakotte, New Mexico State University
Room: UA Student Union Agave

 Friday, October 21, 2011 3:25PM - 3:37PM E3.00001: Magnetic properties of selected Prussian Blue Analogs (PBAs) Manjita Shrestha , Sourav Adak , Heinz Nakotte , Luke L. Daemen , Monika Harlt , Vivien Zapf Prussian Blue Analogs consists of MC$_{6}$ and AN$_{6}$ octahedra connected by cyanide ligands (M, A= metals). They typically crystallize in cubic structures. We have studied temperature and field dependence of the magnetization and the susceptibility of selected Prussian Blue Analogs such as hexacyanocobaltates, -ferrates and -chromates. All compounds exhibit modified Curie --Weiss behavior in the paramagnetic region. The observed effective moments of those compounds were compared with the ones of the respective free-ion values. Furthermore, we find evidence that a few of the compounds exhibit a transition to long-range magnetic order at low temperatures. Friday, October 21, 2011 3:37PM - 3:49PM E3.00002: Local Structural Study of Prussian Blue Analog Fe$_3$(Co(CN)$_6$)$_2$*nD$_2$O Joe Peterson , Sourav Adak , Heinrich Nakotte The family of Prussian Blue analogs (PBA) is of interest because a number of them have been shown to exhibit negative thermal expansion. $Fe_3(Co(CN)_6)_2*nH_2O$ is particularly interesting because, when fully hydrated, it has been shown to have both positive and negative thermal expansion in the region from 123-298K while its partially dehydrated form demonstrates a linear-like negative thermal expansion over the same temperature region. To investigate the role local structural properties play in these systems we conducted temperature varying neutron pair distribution function (PDF) analysis on both the fully hydrated and partially dehydrated $Fe_3(Co(CN)_6)_2*nD_2O$. Friday, October 21, 2011 3:49PM - 4:01PM E3.00003: Thermal Expansion in 3$d$-Metal Prussian Blue Analogs -- A Survey Study S. Adak , L. Daemen , M. Hartl , D. Williams , J. Summerhill , H. Nakotte We present a comprehensive study of the structural properties and the thermal expansion behavior of 17 different Prussian Blue Analogs (PBAs) with compositions $M^{II}_{3}[(M')^{III}$\textit{(CN)}$_{6}]_{2}$\textit{.nH}$_{2}O$ and $M^{II}_{2}$\textit{[Fe}$^{II}$\textit{(CN)}$_{6}$\textit{].nH}$_{2}O$, where $M^{II}$\textit{ = Mn, Fe, Co, Ni, Cu} and \textit{Zn}, $(M')^{III}$\textit{ = Co, Fe} and $n$ = 5 to 18. Temperature-dependent X-ray diffraction studies were performed in the temperature range between -150$^{o}$C (123 K) and room temperature. The vast majority of the studied PBAs were found to crystallize in cubic structures of space groups$Fm\overline 3 m$, $F\overline 4 3m$ and$Pm\overline 3 m$. The temperature dependence of the lattice parameters was taken to compute an average coefficient of linear thermal expansion in the studied temperature range. Of the 17 compounds, 9 display negative values for the average coefficient of linear thermal expansion, which can be as large as 39.7 x 10$^{-6}$ K$^{-1}$ for \textit{Co}$_{3}$\textit{[Co(CN)}$_{6}]_{2.}12H_{2}O$. All of the $M^{II}_{3}$\textit{[Co}$^{III}$\textit{(CN)}$_{6}]_{2}$\textit{.nH}$_{2}O$compounds show negative thermal expansion behavior, which correlates with the Irving-Williams series for metal complex stability. The thermal expansion behavior for the PBAs of the $M^{II}_{3}$\textit{[Fe}$^{III}$\textit{(CN)}$_{6}]_{2}$\textit{.nH}$_{2}O$ family are found to switch between positive (for \textit{M = Mn, Co, Ni}) and negative (\textit{M = Cu, Zn}) behavior, depending on the choice of the metal cation ($M)$. On the other hand, all of the $M^{II}_{2}$\textit{[Fe}$^{II}$\textit{(CN)}$_{6}$\textit{].nH}$_{2}O$ compounds show positive thermal expansion behavior. Friday, October 21, 2011 4:01PM - 4:13PM E3.00004: Preparation and Characterization of Magnetite (Fe$_{3}$O$_{4})$ Nanoparticles Matea Trevino , Karine Chesnel , Betsy Olsen , Jared Hancock , Roger Harrison , Jeffrey Farrer Magnetite (Fe3O4) nanoparticles exhibit a superparamagnetic behavior when small. Our goal is to fabricate such particles and characterize their structural and magnetic properties as function of particle size and synthesis route. I will show the different fabrication methods we have utilized: one inorganic salt mixing method, an inorganic solution method, and lastly an organic solution method. The last approach should allow us to achieve monolayers of nanoparticles. I will present X-ray diffraction (XRD) results as well as Vibrating Sample Magnetometry (VSM) results, including Field Cooling (FC) versus Zero Field Cooling (ZFC) measurements to find the blocking temperature, or when the magnetic moments are frozen; to complement the magnetometry measurements. We will also include images of nanoparticles deposited on a wafer, recorded by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Friday, October 21, 2011 4:13PM - 4:25PM E3.00005: X-ray magnetic scattering studies of Fe3O4 nanoparticles Karine Chesnel , Matea Trevino , Andrew Westover , Roger Harrison , Andreas Scherz Magnetite (Fe3O4) particles exhibit a superparamagnetic behavior when their size are in nanometer scale. Such nanoparticles could potentially be used for applications in the medical field. We are interested in investigating the magnetic order and fluctuation dynamics in self-assemblies of such nanoparticles. Our Fe3O4 nanoparticles are prepared by an organic route and range from 2 nm to 50 nm in size. They are deposited on membranes where they self- assemble. We have been studying the magnetic order using X-ray resonant magnetic scattering (XRMS) at the SSRL synchrotron facility in Stanford. This unique technique, combined with X-ray Magnetic Circular Dichroism (XMCD), provide information about the spatial distribution of the particles and their magnetic interaction. We are studying the magnetic signal under the application of magnetic field and at different temperatures to prepare future dynamical measurements near the blocking temperature.