Oriented attachment and exchange coupling ofα−Fe2O3nanoparticles

Abstract

We show that antiferromagnetic nanoparticles of ␣-Fe 2 O 3 ͑hematite͒ under wet conditions can attach into chains along a common ͓001͔ axis. Electron microscopy shows that such chains typically consist of two to five particles. X-ray and neutron diffraction studies show that both structural and magnetic correlations exist across the interfaces along the ͓001͔ direction. This gives direct evidence for exchange coupling between particles. Exchange coupling between nanoparticles can suppress superparamagnetic relaxation and it may play a role for attachment along preferred directions. The relations between exchange coupling, magnetic properties, and oriented attachment are discussed.

Polarized neutron powder diffraction studies of antiferromagnetic order in bulk and nanoparticle NiO

“…The magnetic correlation length would also be larger than the particle size determined with TEM if the magnetic (and crystallographic) order continues from one particle to the next. This may happen for epitaxially aligned particles [43]. As discussed below, we see no overall preferred orientation of the particles in the sample.…”

Band-gap measurements of bulk and nanoscale hematite by soft x-ray spectroscopy

“…The characterization of a similar "asprepared" sample by the Mössbauer spectroscopy, transmission electron microscopy, x-ray, and neutron diffraction is described in Ref. 29 and discussed below. Samples of ϳ30 nm diameter hematite nanoparticles were produced by annealing commercial NANOCAT ultrafine Fe 2 O 3 ͑MACH I, Inc., King of Prussia, PA͒ in air at 220°C.…”

Interaction of Fe3+meso-tetrakis (2,6-dichloro-3-sulfonatophenyl) porphyrin with cationic bilayers: magnetic switching of the porphyrin and magnetic induction at the interface

“…PP exhibited a decrease in the negative band due to larger symmetry-breaking distortions of the porphyrin in the heterogeneous medium. This feature arises from the contributions of the temperature-independent term [19,58,69]. The S shape and zero crossing of the MCD spectra matched with the electronic absorption maximal most probably results from the magnetic field-induced split of degenerated iron dorbitals (Faraday A term).…”

“…On the other hand, the normally six-coordinate metal center with its four porphyrin ring nitrogen atoms allows the addition of two axial ligands. For design purposes, these axial ligand sites are important for the control of porphyrin properties [19,20].…”