Quantum Well States in Fe(100) Ultrathin Films Observed by Magneto-Optical Effect
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QUANTUM WELL STATES IN Fe(100) ULTRATHIN FILMS OBSERVED BY MAGNETO-OPTICAL EFFECT Yoshishige Suzuki* and Toshikazu Katayaxna Electrotechnical Laboratory, Umezono 1-1-4, Tsukuba, Ibaraki 305, Japan. *National Institute for Advanced Interdisciplinary Research, Higashi 1-1-4, Tsukuba, Ibaraki 305, Japan. ABSTRACT We report on the magneto-optical Kerr rotation(WK) spectra of ultrathin Fe films on Au or Ag (100) substrates and the ýK oscillation due to interlayer thickness in Fe/Au/Fe sandwich films. In 3.5-4.5 eV, a new OK peak appears in the bcc-Fe(100) ultrathin films on the fccAu(100) surface and it shifts towards the higher energy side with increasing Fe layer thickness. The absolute value of Exy for 3A(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 A5 band ({px±i py), fdxz_+i dyzi ; m--+-_) to the Al quantum well states (s, Pz, dz2 ; m=O). The new peak is also observed in the Fe/Au(100) artificial superlattices. Using the exy obtained experimentally for the Fe ultrathin films and the Exx of literature, we can reproduce the experimental OK 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 23 eV. These structures around 2.5 eV are thought to be due to polarized Au atoms adjacent to an Fe layer. An oscillation of OK as a function of interlayer thickness, d, was observed in photon energy region between about 2.5 and 3.8 eV for the Fe(6A)/Au(dA)/Fe(6A) sandwiched film. The oscillation period was about 10A (5ML) of Au. The oscillation is thought to be closely related with a formation of spin polarized quantum well states of Al band in Au layers sandwiched by magnetic layers.
I. INTRODUCTION In this decade, a considerable attention has been focused to 3d-ferromagnetic transition metal/noble metal multilayers, because they have a novel potential to provide a method to control a band structure of magnetic materials and then new interesting phenomena like giant magnetoresistance [11 and oscillating interlayer exchange coupling [2]. Many theoretical and experimental works have been done on the electronic structures of 3d-magnetic ultrathin Mat. Res. Soc. Symp. Proc. Vol. 313. @1993Materials Research Society
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films[3-7]. Measurements of magneto-optical (M-O) effect is very sensitive and useful method [8-101.
Especially, a spectroscopic measurement of magneto-optical effects can provide an
information on magnetic band structures. However, only a few works have been done in the field of the spectroscopy of the magneto-optical effect of ultrathin ferromagnetic films[ 11]. Recently, we have found a new magneto-optical
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