Lecture by Adian Hill, ESRF, Grenoble – Niels Bohr Institute - University of Copenhagen

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Lecture by Adian Hill, ESRF, Grenoble

Since the synthesis of mesoporous silica in 1992, the field of research within the chemical sciences has bloomed. Mesoporous materials (defined as having pores with diameters between 20 Å and 500 Å) have been a regular feature in scientific literature for almost 20 years, with uses such as fuel cells, catalysts, gas storage devices and chemical sponges suggested. This class of material lie between the nano and bulk definitions, exhibiting shared properties between the two worlds. However, very little work has been carried out on studying their magnetic properties and linking these to their physical shape and dimensions. This is in part due to the difficulty of synthesising regularly ordered and repeatable samples.

In 2006, some of the first crystallographically ordered mesoporous metal oxides (ordered walls within an ordered porous structure) were produced. These materials have undergone extensive studies ranging for physisorption analysis to inelastic neutron scattering techniques.

Here I will present the case of mesoporous hematite, α-Fe2O3. Initial magnetic susceptibility measurements showed significant differences between the observed properties and the known properties of bulk hematite. This was confirmed to be the suppression of the well characterised Morin transition (a spin re-orientation) by neutron powder diffraction.

The similarities between this material and extensively studied hematite nanoparticles is striking. Following work by Lefmann et al., we have applied their analysis to inelastic neutron spectroscopy data from the mesoporous sample, using basic approximations. These results, along with the latest high quality data on a nanoparticle sample collected on the upgraded IN5 time of flight spectrometer at the Institut Laue-Langevin will be presented here.