Dresden 2003 – wissenschaftliches Programm
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SYEC: Materials under extreme conditions
SYEC 3: Extreme Conditions (Poster Session)
SYEC 3.1: Poster
Mittwoch, 26. März 2003, 13:00–19:00, P2a
Magnetoelastic effects in cobalt under compression — •Gerd Steinle-Neumann1,2,3, Lars Stixrude2, and Ronald E. Cohen3 — 1Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany. — 2Geological Sciences, University of Michigan, Ann Arbor, MI 48109, USA. — 3Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA.
Recent experiments on cobalt (Co) under compression showed a martensitic phase transition (hexagonal close packed, hcp to cubic close packed, fcc) over an expanded pressure region, ranging from 100 to 150 GPa [1]. The exact location and nature of this phase transition is not well understood to date. It has been speculated, however, that it may be associated with the loss of magnetism at pressure in hcp Co [1] as previously predicted from first-principles calculations [2]. We have used spin-polarized all electron density functional theory with GGA to further study magnetism, energetics, and elasticity for the two phases of Co. In agreement with experiment we find a phase transition at approximately 100 GPa, from ferromagnetic hcp to non-magnetic fcc. Shortly below the transition pressure we find softening of the shear elastic constants (c44 and c66) in hcp Co, in response to the onset of loss of magnetism. We also predict an increase in longitudinal (by ∼ 5 %) and transverse (by ∼ 15%) acoustic velocities across the phase transition.
[1] Yoo et al., Phys. Rev. Lett. 84, 4132 (2000).
[2] Steinle-Neumann et al., Phys. Rev. B 60, 791 (1999).