Heat capacity measurements of
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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.

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University of California at Berkeley – Physics Department – Hellman Lab

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University of california at berkeley physics department hellman lab

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


Motivation

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


Cr fermi surface

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


Gmr sensitivity to interface

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


Relaxation calorimetry on a chip

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


Characteristic specific heat

Low T:

Characteristic specific heat

University of California at Berkeley – Physics Department – Hellman Lab

March APS Meeting – March 13, 2008


Heat capacity of mmls

Heat capacity of MMLs

University of California at Berkeley – Physics Department – Hellman Lab

March APS Meeting – March 13, 2008


Sommerfeld values for mmls

Sommerfeld values for MMLs

University of California at Berkeley – Physics Department – Hellman Lab

March APS Meeting – March 13, 2008


Tri layer model

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


Sommerfeld values for mmls1

Sommerfeld values for MMLs

University of California at Berkeley – Physics Department – Hellman Lab

March APS Meeting – March 13, 2008


Mml characterization

MML Characterization

University of California at Berkeley – Physics Department – Hellman Lab

March APS Meeting – March 13, 2008


Xrd of mmls

XRD of MMLs

University of California at Berkeley – Physics Department – Hellman Lab

March APS Meeting – March 13, 2008


Conclusions

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


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