1. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 Heat capacity measurements of sub- milligram quantities of mantle minerals David W. Cooke, Frances Hellman University of California, Berkeley Alexandra Navrotsky, Maria Dorogova, Charles E. Lesher University of California, Davis

2. Magnetic Phase Transitions? Structural Phase Transitions? University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 Motivation High pressure materials –Lower mantle, D’’ layer, and core –Silicate spinels,(Mg,Fe) 2 SiO 4 –Effect of minor constituents in silicate phases –Perovskites (Mg,Fe)SiO 3 –Stishovite (rutile SiO 2 ) Small sample size –Multi-anvil cells: ~100-10,000 µg –Diamond anvil cells: ~1-100 µg

3. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 “Calorimeter on a Chip” Specific heat of thin films –100nm ~= 5µg –2K - 500K –0T - 8T Information gained: –Thermodynamics Decomposition Magnetic transitions Structural changes 2006 APS Keithley Instrumentation Award

4. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 Simulation Work

5. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 Relative Addenda Size

6. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 Fe 2 SiO 4 Olivine (Fayalite) High T difference likely due to silver paint addenda uncertainty

7. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 Cobalt Oxide High T difference likely due to silver paint addenda uncertainty

8. Synthesized by multi-anvil apparatus (UCD) (Lesher’s lab) –Powder with grains ~5-50µg –XRD shows pure spinel phase University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 Fe 2 SiO 4 Spinel High pressure phase formed from olivine, composition [(Fe,Mg) 2 SiO 4 ] Found in mantle transition zone Fe 2 SiO 4 olivine spinel transition near 6 GPa

9. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 Fe 2 SiO 4 Spinel Data noisier because used “large” device (C P of spinel ~16% total C P )

10. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 15, 2006 Conclusions/Future Work Shown feasibility of new technique Measure silver paint C P to higher accuracy Decrease addenda by using thin devices Improve measurements on pure fayalite Measure Mg 2-x Fe x SiO 4 series –Relevant to transition zone geophysics –Are there magnetic transitions?