NMR Study of $\varepsilon $-Co Nanoparticles

POSTER

Abstract

$^{59}$Co spin-echo nuclear magnetic resonance (NMR) spectra were obtained at 4.2 K and 1.3 K for a 6.5 nm $\varepsilon $-Co nanoparticle system. The powder sample was synthesized using an air-free high boiling point solution procedure and sealed in glass ampules without exposure to air. No NMR signal is observed at either 4.2 K or 1.3 K over the frequency range 150 MHz $<$= $\nu \quad <$= 250 MHz for H = 0; however, the application of a magnetic field 1.5 kOe $<$= H $<$= 7.5 kOe results in the appearance of a very strong echo. The NMR spectra are characterized by two components: (1) a distinct peak at 232 MHz whose intensity increases but does not shift with increasing field and (2) a very broad distribution between 150 MHz and 210 MHz whose intensity both increases and shifts to higher frequency with increasing field. There is no trace of the peaks which characterize either the multidomain or single domain fcc or hcp phases. Furthermore, a dramatic time evolution of the echo (observed at both 205 MHz and 232 MHz) is observed when the field is suddenly increased or decreased. An attempt to understand the spectra in the light of a core-shell picture for the $\varepsilon $-Co nanoparticles, superparamagnetism, and the interparticle and intraparticle interactions is made.

Authors

  • David Perry

    University of Connecticut, Department of Physics, University of Connecticut, Storrs, CT 06269-3046

  • Joseph Budnick

    University of Connecticut, Department of Physics, University of Connecticut, Storrs, CT 06269-3046

  • William Hines

    Department of Physics, University of Connecticut, Storrs, CT 06269-3046

  • V.E. Guiseppe

    University of Connecticut, Univ. of New Hampshire, Sandia National Labs, IBM Research Center, PTB, TUNL, Petersburg Nuc. Phys. Inst., Yale Univ., U.S. Coast Guard Acad., Department of Physics, University of Connecticut, Storrs, CT 06269-3046, Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, Division of Proton Engineering Frontier Project, Korea Atomic Energy Research Institute, Daejeon, Korea, Department of Chemistry, Sogang University, Seoul, Korea, Materials Science Department, Brookhaven National Lab, Upton, NY 11973, Canadian Light Source, University of Saskatchewan, Saskatoon, Canada, Department of Physics, University of Connecticut, Storrs, CT 06269, RMD Inc., Watertown, MA, ALEM Associates, Boston, MA, Physics Department, University of Connecticut, Storrs, CT, University of South Dakota, LANL

  • V.E. Guiseppe

    University of Connecticut, Univ. of New Hampshire, Sandia National Labs, IBM Research Center, PTB, TUNL, Petersburg Nuc. Phys. Inst., Yale Univ., U.S. Coast Guard Acad., Department of Physics, University of Connecticut, Storrs, CT 06269-3046, Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, Division of Proton Engineering Frontier Project, Korea Atomic Energy Research Institute, Daejeon, Korea, Department of Chemistry, Sogang University, Seoul, Korea, Materials Science Department, Brookhaven National Lab, Upton, NY 11973, Canadian Light Source, University of Saskatchewan, Saskatoon, Canada, Department of Physics, University of Connecticut, Storrs, CT 06269, RMD Inc., Watertown, MA, ALEM Associates, Boston, MA, Physics Department, University of Connecticut, Storrs, CT, University of South Dakota, LANL