Direct determination of the magnetic structure of the delta phase of oxygen.
Simple diatomic molecules exhibit a variety of exciting physical phenomena under high pressures, including structural transitions, pressure induced metallization, and superconductivity. Oxygen is of particular interest because it carries a magnetic moment. For the first time we studied the magnetic structure in solid oxygen under very high pressure by a direct method, namely, neutron diffraction. A new type of magnetic order with ferromagnetic stacking of the antiferromagnetic O2 planes was discovered in delta-O2 at P=6.2 GPa. We show that all structural transformations at pressures <7 GPa are driven by spin interactions; therefore, high-pressure oxygen should be considered as a unique "spin-controlled crystal."
Laboratoire Léon Brillouin C.E.A.-C.N.R.S., CEA Saclay, 91191 Gif-sur-Yvette, France.
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Goncharenko
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Makarova
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Ulivi