1. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 Heat capacity measurements of Fe/Cr multi-layers David W. Cooke, Frances Hellman University of California, Berkeley Matt Carey Hitachi Global Storage Technologies San Jose Research Center

2. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 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 How to measure DOS?

3. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 Cr Fermi Surface Mattheis, 1965; Laurent, 1981; Fawcett, 1988 (100) plane

4. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 GMR Sensitivity to interface D.T. Pierce, J.A. Stroscio, J. Unguris, R.J. Celotta, PRB 49 (1994). M. Velez and I. K. Schuller, J. Mag. Mag. Mat. 184, 275 (1998). M.C. Cyrille, S. Kim, M. E. Gomez, J. Santamaria, C. Leighton, Kannan, M. Krishnan, and Ivan K. Schuller, PRB 62 (2000).

5. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 Relaxation Calorimetry on a Chip Specific heat of thin films –200nm ~= 10µg –2K - 300K –0T - 8T 2006 APS Keithley Instrumentation Award Magnetron sputtered MMLs –t Fe constant @ 17.7A –Film thickness ~200nm –Substrate at RT Thermally evaporated Cu –~200nm thick –High k yields uniform temperature contours

6. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 Characteristic specific heat Low T:

7. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 Heat capacity of MMLs

8. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 Sommerfeld values for MMLs

9. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 Tri-layer model Chromium Fe/Cr Alloy Iron mJ/mol.K 2 !!!

10. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 Sommerfeld values for MMLs

11. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 MML Characterization

12. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 XRD of MMLs

13. University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008 Conclusions Fe/Cr MMLs exhibit well-defined enhancement of D.O.S. at Fermi energy –No field dependence –GMR-independent –Suggests interface effect Future directions: –More textured films –Vary roughness via sputtering pressure –Study of alloys