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This presentation discusses the impact of disorder on the heat capacity of Chromium films, exploring the interaction between short- and long-range coupling terms in the material. Key findings on stress, disorder, and electron-phonon coupling are presented, highlighting the influence of disorder on phonon softening and electron-phonon interactions. The study also examines the Fermi surface, spin density waves, and critical points related to disorder in Chromium films. The presentation concludes with insights on disorder broadening effects and the implications for data storage and magnetic sensors.
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Heat capacity measurements of disordered Cr films David W. Cooke, Zoe Boekelheide, Daniel R. Queen, Frances Hellman University of California, Berkeley University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 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 FM University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008
Motivation “Rough” “Smooth” Pierce, Stroscio, Unguris, Celotta, J.Mag.Mag.Mat200 (1999) • 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, PRL77, 1382 (1996) University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008
Cr Fermi Surface & SDW AF1 AF2 ISDW AF0 CSDW Kummamuru, Soh. Nature 452 (2008) University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008
Stress, Disorder, & the SDW Boekelheide et al., PRB 76 (2007) University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008
How to measure the DOS? Si Frame Thermometers Heater Membrane Thin Film Sample Denlinger, Abarra, Allen, Rooney, Messer, Watson, and Hellman. Rev. Sci. Instr.65, 946 (1994) University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008
Mixed SDW CSDW ISDW CP Results • Different slopes equal different Debye temps. • High temperature values collapse • Increasing γ with increasing disorder ӨD = 405K γ =6.5 γ =1.55 ӨD = 585K University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008
c E-P coupling and the DOS McMillan, Phys. Rev. 167 (1968) (a,b,c) Bulk data references: γ, ӨD from a) Heiniger et al. Phys. kondens. Materie5 (1966), N(ε) from b) Laurent, et al. PRB 23 (1981), and from c) Brorson, et al. PRL64 (1990). University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008
Disorder Broadening University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008
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 University of California at Berkeley – Physics Department – Hellman Lab MMM Conference (Austin, TX) – November 13, 2008
