1. University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008 Heat capacity measurements of disordered Cr films David W. Cooke, Zoe Boekelheide, Daniel R. Queen, Frances Hellman University of California, Berkeley

2. University of California at Berkeley – Physics Department – Hellman Lab Motivation Nobel Prize Committee – 2007: “The discovery of giant magnetoresistance immediately opened the door to a wealth of new scientific and technological possibilities, including a tremendous influence on the technique of data storage and magnetic sensors.” FM NM MMM Conference (Austin, TX) – November 13, 2008

3. University of California at Berkeley – Physics Department – Hellman Lab Motivation Pierce, Stroscio, Unguris, Celotta, J.Mag.Mag.Mat 200 (1999) “Rough”“Smooth” Spin density wave AFM sets short- range coupling in Fe/Cr MMLs Roughness can lead to frustration Alters competition between short- and long-range coupling terms Fullerton, Bader, Robertson, PRL 77, 1382 (1996) MMM Conference (Austin, TX) – November 13, 2008

4. University of California at Berkeley – Physics Department – Hellman Lab Cr Fermi Surface & SDW Kummamuru, Soh. Nature 452 (2008) ISDW CSDW AF 1 AF 2 AF 0 MMM Conference (Austin, TX) – November 13, 2008

5. University of California at Berkeley – Physics Department – Hellman Lab Stress, Disorder, & the SDW Boekelheide et al., PRB 76 (2007) MMM Conference (Austin, TX) – November 13, 2008

6. University of California at Berkeley – Physics Department – Hellman Lab How to measure the DOS? Denlinger, Abarra, Allen, Rooney, Messer, Watson, and Hellman. Rev. Sci. Instr. 65, 946 (1994) Si Frame Heater Thermometers Thin Film Sample Membrane MMM Conference (Austin, TX) – November 13, 2008

7. University of California at Berkeley – Physics Department – Hellman Lab C P Results ISDW CSDW Mixed SDW Different slopes equal different Debye temps. High temperature values collapse Increasing γ with increasing disorder Ө D = 585K Ө D = 405K γ = 6.5 γ =1.55 MMM Conference (Austin, TX) – November 13, 2008

8. University of California at Berkeley – Physics Department – Hellman Lab Phonon Softening Wühl, et al. Z. Physik B 38 (1980) Ewert, et al. Sol. St. Comm. 18, 923 (1976) Features in F(ω) spread out and become more heavily weighted at low energies. MMM Conference (Austin, TX) – November 13, 2008

9. University of California at Berkeley – Physics Department – Hellman Lab E-P coupling and the DOS McMillan, Phys. Rev. 167 (1968) c Bulk data references: γ, Ө D from a) Heiniger et al. Phys. kondens. Materie 5 (1966), N(ε) from b) Laurent, et al. PRB 23 (1981), and from c) Brorson, et al. PRL 64 (1990). (a,b,c) MMM Conference (Austin, TX) – November 13, 2008

10. University of California at Berkeley – Physics Department – Hellman Lab Disorder Broadening MMM Conference (Austin, TX) – November 13, 2008

11. University of California at Berkeley – Physics Department – Hellman Lab Conclusions Within error, there is no observable difference in N between ISDW and CSDW Increasing disorder leads to phonon softening, as expected Strongly disordered samples show a strongly enhanced electron-phonon coupling Disorder broadening accounts for the variation in N MMM Conference (Austin, TX) – November 13, 2008