The Magneto-Optical Quantum Size Effect in bcc-Fe(001) and (110) Ultrathin Films
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W. GEERTSb, P. BRUNOc, and H. SAWADAa
aJoint Research Center for Atom Technology-National Institute for Advanced Interdisciplinary Research (JRCAT-NAIR), 1-1-4, Higashi, Tsukuba, IBARAKI 305, Japan. bElectrotechnical Laboratory, 1-1-4, Umezono, Tsukuba, IBARAKI 305 Japan. CInstitut d' .lectroniqueFondamentale, Bat. 220, CNRS URA 22, Universit6 Paris-Sud, 91405 ORSAY, France. Abstract Recently, the oscillation of the magneto-optical effect with respect to the ferromagnetic layer thickness was observed for bcc-Fe(001) ultrathin films. The oscillation periods have been explained by the theory concerning the formation of quantum well states in the ferromagnetic layer. In this paper, a physical picture how the electron confinement produces the quantum size effect of the magneto-optical responses is introduced, and experimental results on the magnetooptical effects of the bcc-Fe films of different orientations are presented. The (001) oriented films show clear oscillation. On the other hand, the (110) oriented films does not show any oscillation. The reason is discussed from the band structure and growth modes. 1. INTRODUCTION By continuous efforts of many researchers in the field of magnetic ultrathin films and multilayers, now, it is available to control the thickness of magnetic layers within monatomic layer level, although it is really possible only for several special combinations of substrates and overlayers. This new technology allows us to investigate some basic physical properties like oscillating magnetic interlayer coupling, giant magneto-resistance and interface magnetism, and "alsogives us opportunities to create new application devices based on such physical properties of the magnetic ultrathin films and multilayers [1]. In those findings and inventions, the interference of the scattered electron in the ultrathin metallic multilayers have been playing a central role. In a well defined ultrathin film, an interference of the electrons which are scattered at the interfaces composes a confined state (quantum well states and resonance states) in the film. The oscillation of the exchange coupling of two ferromagnetic layers through non-magnetic spacerlayer [2] can be explained by the occurrence of spin polarized quantum well states (QWS) at the Fermi energy in the nonmagnetic spacer layer [3]. The exchange coupling oscillates also as a function of ferromagnetic layer thickness [4] due to an occurrence of QWS at the Fermi energy in the ferromagnetic layers [5]. A lot of experimental data on the influence of the spacer layer on the coupling character can be found in literature. Such QWS's of occupied states and unoccupied states in metallic systems have been observed directly by the photoemission spectroscopy [6] and the inverse photoemission spectroscopy [7]. In 1992, it was also shown that the QWS's could have large contributions to the magnetooptical (MO) effect [8]. Oscillations of magneto-optical Kerr rotation and/or ellipticity as a function of ferromagnetic layer thickness in Au/Fe/Au(001) [9] and the nonma
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