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Photoemission study of coupled magnetic layers

Photoemission study of coupled magnetic layers. Z. Q. Qiu Dept. of Physics, University of California at Berkeley. Outline Motivation Magnetic Phase Transition Spin Reorientation Transition Wish List. 2D. 1D. 0D. 5ML. 10. 15. 20. 25. 30. Motivation. GMR and Oscillatory Coupling

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Photoemission study of coupled magnetic layers

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  1. Photoemission study of coupled magnetic layers Z. Q. Qiu Dept. of Physics, University of California at Berkeley • Outline • Motivation • Magnetic Phase Transition • Spin Reorientation Transition • Wish List

  2. 2D 1D 0D 5ML 10 15 20 25 30 Motivation • GMR and Oscillatory Coupling • P. Grünberg, et. al., Phys. Rev. Lett. 57, 2442 (1986). • M. N. Baibich, et. al., Phys. Rev. Lett. 61, 2472 (1988). • S. S. P. Parkin et. al. Phys. Rev. Lett. 64, 2304 (1990). Spectroscopy of valence electrons Microscopy of core electrons (PEEM) • Element-specificity + imaging • How does the interlayer coupling change the magnetic properties • of the individual layer?

  3. ? TC1 TC2 FM1 FM2 FM2 FM1 Ni(wedge)/Fe(5ML)/Co(10ML)/Cu(100) Co Co Ni Ni dc T=310K 380K 430K Magnetic Phase Transition • What is effect of the interlayer coupling on the phase transition? • Single or separate phase transitions? • How is the TC of the coupled sandwich compared to TC1 and TC2? Ni(3ML)/Fe(5ML)/Co(10ML)/Cu(100)

  4. Co Co(0.23ML)/Cu(2ML)/Ni/Cu(100) dCo= 0.23ML 0.23ML 0.23ML 0.23ML 0.23ML Co Ni dCo= 1.3ML 1.3ML 1.3ML 1.3ML 1.3ML dNi = 4.9ML 5.3ML 5.8ML 6.2ML 7.1ML Ni Co(2.3ML)/Cu(2ML)/Ni/Cu(100) dNi = 3.7ML 4.5ML 5.0ML 5.4ML 6.1ML Co dCo= 2.3ML 2.3ML 2.3ML 2.3ML 2.3ML Ni dNi =2.5ML 3.4ML 4.1ML 5.3ML 7.5ML Co(1.3ML)/Cu(2ML)/Ni/Cu(100)

  5. Co/Cu(2ML)/Ni/Cu(100) Co/Fe(5ML)/Ni/Cu(100) • PM state of one layer has little effect on the Tc of the other film. • FM state of one layer reduces the dc of the other layer.

  6. dNi II 1: PM 2: FM IV 1: FM 2: FM I 1: PM 2: PM III 1: FM 2: PM dCo Jint=0 Jint0 dNi II 1: PM 2: FM IV 1: FM 2: FM I 1: PM 2: PM III 1: FM 2: PM dCo

  7. ? K  0 K > 0 K < 0 Spin Reorientation Transition (SRT) H = -J  Si•Sj – KSiz2 What will happen at K  0 ? • Spin-orbit interaction gives -KSZ2 if z symmetry is broken. • Dipolar interaction gives 2pM2SZ2. E = -KSZ2 = -(KS/d - 2pM2)SZ2 Changing d or T to tune K around zero.

  8. equals If M2/ r  0, E = -J M1•M2= - M1 •Hwith H = J <M2> M1 M1 How do the stripe domains respond to H ? M2 • Electron microscope is used for domain imaging. • It is difficult to apply H in an electron microscope. • SRT of M1 in a coupled sandwich for H=0 is equivalent to the SRT of M1 single layer within a H=J< M2>. H = 0 H = J<M2>  0 • Electron Microscope can be used to study stripe domains as a function of “magnetic field”.

  9. Co H = JMCo Cu • Sample is grown by MBE. • Fe/Ni(5ML) film as the SRT layer. • Cu/Co(10ML) provides the in-plane magnetic field. Fe/Ni Cu(001)

  10. Fe thickness (ML) 2.4ML 2.6ML 2.8ML  50mm // (a) (b) (c) 10mm

  11. 15mm Co Fe 15mm Co(10ML)/Cu/Fe/Ni(5ML)/Cu(001) The Co magnetization (in-plane field) aligns the stripe domains of the Fe/Ni layer.

  12. 50mm 6.9ML H FC K dCu(ML) AFC 6.3ML 2.44ML 2.84ML dFe(ML) Co(10ML)/Cu/Fe/Ni(5ML)/Cu(001)

  13. (a) 2.59ML 2.66ML 2.72ML dFe=2.53ML (b) 6.66ML 6.73ML 6.81ML dCu=6.57ML (c) 6.47ML 6.38ML 6.27ML dCu=6.57ML

  14. w x L z w q mH=Jint q y

  15. Fe thickness (ML) 2.4ML 2.6ML 2.8ML  50mm // (a) (b) (c) 10mm Discussion of Jint=0.

  16. Discussion

  17. Wish List • Develop techniques that are unique for certain type of problems (e.g., element-specificity). • Attract users who are doing outstanding research on magnetic nanostructures, but not yet using synchrotrons. • Keep pushing the spatial resolution down to nm for laterally • modulated structures (vicinal surfaces, wires, and dots …). • Element-specific measurement of antiferromagnetic materials • other than oxides (Mn, Cr, FeMn). • Microscopy within magnetic field. • Fast spin Dynamics (t<1-10ps). • Improve in-situ sample preparation capability.

  18. Collaborators • Department of Physics, University of California at Berkeley • Y. Z. Wu, C. Won, and H. W. Zhao • Advanced Light Source, Lawrence Berkeley National Laboratory • A. Doran and A. Scholl • Department of Physics, Fudan University • X. F. Jin Thank you!

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