Quantum Well States in Fe(100) Ultrathin Films Observed by Magneto-Optical Effect


We report on the magneto-optical Kerr rotation(ϕκ) spectra of ultrathin Fe films on Au or Ag (100) substrates and the ϕκ oscillation due to interlayer thickness in Fe/Au/Fe sandwich films. In 3.5-4.5 eV, a new ϕκ peak appears in the bcc-Fe(100) ultrathin films on the fcc-Au(100) surface and it shifts towards the higher energy side with increasing Fe layer thickness. The absolute value of ɛXy for 3Å(2ML) thick Fe layers is twice as large as that of bulk Fe at 3.7 eV. The thickness dependence of the transition energy of this new peak in the spectra is well explained by the concept of quantum well states in the Fe ultrathin layers, attributing the new transition to a transition from the majority spin Δ5 band ({px±i py}, {dxz±i dyZ}; m=±l) to the Δ1 quantum well states (s, pz, dz2; m=0). The new peak is also observed in the Fe/Au(100) artificial superlattices. Using the εXy obtained experimentally for the Fe ultrathin films and the εxy of literature, we can reproduce the experimental φκ spectra of the artificial superlattices by optical calculation. On the other hand, we cannot observe the same behavior for the ultrathin Fe films grown on a fcc-Ag(100) surface and covered by a Au(100) ultrathin film, although the eXy of Fe is different from that of the bulk and shows some structures in 2–3 eV. These structures around 2.5 eV are thought to be due to polarized Au atoms adjacent to an Fe layer.

An oscillation of φκ as a function of interlayer thickness, d, was observed in photon energy region between about 2.5 and 3.8 eV for the Fe(6Å)/Au(dÅ)/Fe(6Å) sandwiched film. The oscillation period was about 10Å (5ML) of Au. The oscillation is thought to be closely related with a formation of spin polarized quantum well states of Δ1 band in Au layers sandwiched by magnetic layers.

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The authors would like to express their gratitude to Prof. K.Sato of Tokyo University of Agriculture and Technology for ellipticity measurements, and to Mr. M.Hayashi of Nihon University for Kerr rotation measurements. The authors also would like to acknowledge to Dr. K.Ando, Dr. W.Geerts, Dr. A.Thiaville, and Dr. S.Yoshida of Electrotechnical Laboratory, and Dr.K.Tanaka of National Institute for Advanced Interdisciplinary Research for useful discussions.

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Correspondence to Yoshishige Suzuki.

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Suzuki, Y., Katayama, T. Quantum Well States in Fe(100) Ultrathin Films Observed by Magneto-Optical Effect. MRS Online Proceedings Library 313, 153–164 (1993). https://doi.org/10.1557/PROC-313-153

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