Evidence of Formation of Superdense Nonmagnetic Cobalt.
Because of the presence of 3d transition metals in the Earth's core, magnetism of these materials in their dense phases has been a topic of great interest. Theory predicts a dense face-centred-cubic phase of cobalt, which would be nonmagnetic. However, this dense nonmagnetic cobalt has not yet been observed. Recent investigations in thin film polycrystalline materials have shown the formation of compressive stress, which can increase the density of materials. We have discovered the existence of ultrathin superdense nonmagnetic cobalt layers in a polycrystalline cobalt thin film. The densities of these layers are about 1.2-1.4 times the normal density of Co. This has been revealed by X-ray reflectometry experiments, and corroborated by polarized neutron reflectometry (PNR) experiments. Transmission electron microscopy provides further evidence. The magnetic depth profile, obtained by PNR, shows that the superdense Co layers near the top of the film and at the film-substrate interface are nonmagnetic. The major part of the Co film has the usual density and magnetic moment. These results indicate the possibility of existence of nonmagnetic Co in the earth's core under high pressure.
Department of Materials Science, Indian Association for the Cultivation of Science, 2A &2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India.
Nasrin
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Banu
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
Surendra
S
Singh
Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064, India.
B
B
Satpati
Microelectronic Research Center, The University of Texas at Austin, 10100 Burnet Road, Bldg 160, MER 1.606J, Austin, Texas 78758, USA.
A
A
Roy
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
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S
Basu
Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064, India.
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P
Chakraborty
Microelectronic Research Center, The University of Texas at Austin, 10100 Burnet Road, Bldg 160, MER 1.606J, Austin, Texas 78758, USA.
Hema C P
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Movva
Quantum Condensed Matter Division, Neutron Science Directorate, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN 37831-6475, USA.
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V
Lauter
Department of Materials Science, Indian Association for the Cultivation of Science, 2A &2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India.
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Dev