Magnetic instabilities in invar

A theory of magnetic instabilities which qualitatively explains the anomalous thermal properties of invar is presented. Fixed-spin-moment band calculations are used to show the existence of two-spin-states similar to Weiss's 2γ-state model. The two spin-states are connected by magnetic instabil...

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Bibliographic Details
Published in:Physica. B, Condensed matter Condensed matter, 1990-01, Vol.161 (1-3), p.99-104
Main Author: Moruzzi, V.L.
Format: Article
Language:English
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Summary:A theory of magnetic instabilities which qualitatively explains the anomalous thermal properties of invar is presented. Fixed-spin-moment band calculations are used to show the existence of two-spin-states similar to Weiss's 2γ-state model. The two spin-states are connected by magnetic instabilities which are shown to occur near the equilibrium volume in the Fe-Ni invar alloy with approximately 8.6 valence electrons/atom. The consequences of lattice vibrations on the thermal occupation of the two states are examined and it is shown that the low temperature expansion is dominated by a high-spin state, while the high temperature expansion results from a composite occupation of a high-spin and a low-spin state. The initial negative thermal expansion is shown to result from an antiferromagnetic state.
ISSN:0921-4526
DOI:10.1016/0921-4526(89)90112-9