Elasticity of Ferro- Periclase Through the High Spin - Low Spin Transition J. Michael Brown - University of Washington Jonathan Crowhurst - Lawrence Livernmore Lab. Alexander Goncharov - Geophysical Lab. Steven Jacobsen - Northwestern University J. Michael Brown - University of Washington Jonathan Crowhurst - Lawrence Livernmore Lab. Alexander Goncharov - Geophysical Lab. Steven Jacobsen - Northwestern University

Summary (Three Major Topics)  Mantle Tomography: Why are slabs hard to image in the lower mantle?  Do not penetrate?  Off-setting chemical and thermal effects?  High spin - low spin transition?  Mantle Tomography: Why are slabs hard to image in the lower mantle?  Do not penetrate?  Off-setting chemical and thermal effects?  High spin - low spin transition?

Summary (Three Major Topics)  Mantle Tomography: Why are slabs hard to image in the lower mantle?  Do not penetrate?  Off-setting chemical and thermal effects?  High spin - low spin transition?  Mantle Tomography: Why are slabs hard to image in the lower mantle?  Do not penetrate?  Off-setting chemical and thermal effects?  High spin - low spin transition?

 Physics of the High spin low spin transition  Outstanding experimental data  Robust macroscopic thermodynamic theory  Physics of the High spin low spin transition  Outstanding experimental data  Robust macroscopic thermodynamic theory

 New measurements of sound velocities through the HS-LS transition  Some experimental details  All elastic constants determined to 63 GPa  Help validate the macroscopic thermodynamic description  Support idea that thermal anomalies have small velocity perturbations in lower mantle  New measurements of sound velocities through the HS-LS transition  Some experimental details  All elastic constants determined to 63 GPa  Help validate the macroscopic thermodynamic description  Support idea that thermal anomalies have small velocity perturbations in lower mantle

Less structure in lower mantle A possible connection to the high-spin low-spin transition “Using the best mineral physics data, slabs should be visible in seismic images of the mid lower mantle - that they are not seen is somewhat surprising” Guy Masters 2006 AGU meeting

Physics of the High spin to Low spin Transition

High spin - low spin iron  Transition is  Intrinsically non-1 st order  Readily described by robust macroscopic thermodynamics  Characterized by  H =  E + P  V  Associated with anomalies in physical properties  Transition is  Intrinsically non-1 st order  Readily described by robust macroscopic thermodynamics  Characterized by  H =  E + P  V  Associated with anomalies in physical properties

 Truly exciting both in terms of  High pressure physics and chemistry  Understanding Earth’s mantle But - some re-appraisals are needed  Truly exciting both in terms of  High pressure physics and chemistry  Understanding Earth’s mantle But - some re-appraisals are needed

Clapyron Slope

Low-spin iron is an “additional chemical component in the mantle”

Fine Print  Focus on (Mg,Fe)O -  similar behavior for Perovsikte?  LS iron has smaller “ionic radius”  D-orbitals directed where oxygen is not  Iron sites are non-interacting  Properties in proportion to iron concentration  Little difference in EOS of HS and LS iron  “Softening” expected in transition region  Increment of pressure causes “normal” strain plus additional strain with HS to LS transition  If spin flip is “fast” compared to acoustic frequency, velocities can decrease  Focus on (Mg,Fe)O -  similar behavior for Perovsikte?  LS iron has smaller “ionic radius”  D-orbitals directed where oxygen is not  Iron sites are non-interacting  Properties in proportion to iron concentration  Little difference in EOS of HS and LS iron  “Softening” expected in transition region  Increment of pressure causes “normal” strain plus additional strain with HS to LS transition  If spin flip is “fast” compared to acoustic frequency, velocities can decrease

Macroscopic Thermodynamics  Gibbs energy: G(P,T,n,x)  n is low spin occupation (0 to 1)  x is fraction of sites occupied by Fe (0 to 1)  G = G lattice + G vibration + G magnetic + G mixing  Minimize G with respect to n  Gibbs energy: G(P,T,n,x)  n is low spin occupation (0 to 1)  x is fraction of sites occupied by Fe (0 to 1)  G = G lattice + G vibration + G magnetic + G mixing  Minimize G with respect to n

m = degeneracy (3) S = Spin state (2)  H =  E + P  V Tsuchiya et al 2006 also: Slichter and Drickamer 1972, G ü tlich et al 1979

Theory vs Experiment?

New Experimental Data

Impulsive Stimulated Light Scattering

(Mg,Fe)O 5.6% Fe (100) surface Ruby Argon 50 microns Rhenium Gasket

Extension to High Temperature?

Intrinsic Spin TransitionTotal Predicted Seismic Structure

SUMMARY  Large anomalies in V p and V s for HSLS transition  Macroscopic thermodynamic description works  Tested vs pressure and composition  High temperature test is needed  Mantle velocity anomalies may be suppressed - d V/ d T HSLS > 0  Explanation for lack of mid-mantle tomographic structure?  Perovskite is presumed to have analogous behavior  Large anomalies in V p and V s for HSLS transition  Macroscopic thermodynamic description works  Tested vs pressure and composition  High temperature test is needed  Mantle velocity anomalies may be suppressed - d V/ d T HSLS > 0  Explanation for lack of mid-mantle tomographic structure?  Perovskite is presumed to have analogous behavior