Trinity College Dublin

Extra Terrestrial Magnetic Carbon

Persistent reports of very weak high temperature ferromagnetism in graphite [ Ref:Magnetic carbon Tatiana L. Makarova et al, Ref Ferromagnetism in Oriented Graphite Samples P. Esquinazi et al] received a boost from our recent studies of graphite nodules from the Canyon Diablo meteorite. Pieces of the huge Fe-Ni fall from the Arizona desert contain large graphite inclusions which are shot through with metal on all length scales from ten nanometres to ten millimetres. Strongly ferromagnetic, only about two thirds of the magnetisation can be accounted for by the magnetic minerals present - kamacite, magnetite, etc. The residue, with a magnetization of 23 A m2 kg-1 is somehow associated with carbon! We propose that the moment is induced in a sheath that is surrounding nanoscale magnetite inclusions - a magnetic proximity effect. The combination of half-metal and semi-metal (magnetite/graphite) opens a new dimension in spin electronics.

Nature paper

Magnetic Soils

Some tropical soils are sufficiently magnetic to be attracted by a small magnet (there are no such soils in Ireland). We have been interested in how the magnetic minerals maghemite and magnetite form in the soils and how magnetic measurements on the field can help in agronomy. A portable soil magnetometer has been developed for this purpose. There are even implications for use on Mars. Ref: The magnetic soils of Brazil, Mauro Resende, J.E.M. Allan and J.M.D. Coey, Earth Planet. Sci.Lett. 78 322-326 (1986), A portable soil magnetometer, J M D Coey, O Cugat, J McCauley and J D Fabris, Revista de Fisica Aplicada e Instrumentação 7 25-30 (1993)