University of California at Berkeley – Physics Department – Hellman Lab

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

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

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

4. GMR Sensitivity to interface 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, PRB62 (2000). D.T. Pierce, J.A. Stroscio, J. Unguris, R.J. Celotta, PRB49 (1994). University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008

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

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

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

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

9. mJ/mol.K2!!! Tri-layer model Chromium Fe/Cr Alloy Iron University of California at Berkeley – Physics Department – Hellman Lab March APS Meeting – March 13, 2008

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

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

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

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