Fe on Au(100): Quantum-well states down to a monolayer

Abstract

Quantum-well states are observed for Fe films embedded in Au(100) using inverse photoemission.They can be analyzed with a simple interferometer model, using bulk states from the I &26&H» band that are modulated by an envelope function with wavelengths in the order of 7-10 atomic layers (10-14 A). These states can be followed down to a monolayer, where two states are seen at 0.6 and 1.9 eV. They are tentatively assigned to the 551 monolayer state and a A~quantum-well state. The resulting ferromagnetic exchange splitting of the h, q state is 2.7 eV, exceeding the splitting of 1.8-2. 1 eV for the analogous bulk band.The attempts to fabricate ever finer quantum structures, such as superlattices and quantum wells, are approaching the atomic limit. The study presented here makes the connection from a narrow but still bulklike quantum well to a monolayer quantum well. The latter is strongly inAuenced by interface phenomena since the atoms in the well are all interface atoms. The transition from conventional quantum-well states to monolayer states is observed with inverse photoemission. In contrast to previously studied quantum wells, such as semiconductors and noble metals, the system considered here consists of a ferromagnetic well, all the way down to a monolayer.In the monolayer limit a ferromagnetic exchange splitting of 2.7 eV is found for the 5, & state, which is significantly larger than the splitting of 1.8-2. 1 eV for the analogous bulk band. This confirms predictions of enhanced monolayer magnetism.The Fe/Au(100) system is suited particularly well for the purpose of creating narrow quantum wells. There is a good lattice match (better than 1%), with the lattice constant of fcc Au a factor of J2 larger than that of bcc Fe. This provides a one-to-one match of the (100) surface lattices, due to the extra face-centered atom in Au. The two band structures, however, are quite different from each other, thereby providing a large band offset and well depth of 9 eV. This is an order of magnitude larger than in any other quantum-well system studied to date. ' As a consequence, the exponential decay of the wave function is extremely fast in the barrier region, thereby confining the states to the well within a single layer. The growth of Fe on Au(100) has been found to proceed layer-by-layer, with one layer of Au staying on top of the growing Fe surface. This Au overlayer acts as a surfactant by lowering the surface energy of the growing film and thereby preventing island formation. The resulting uniformity of the Fe film makes it possible to see variations in the electronic structure on a layer-by-layer basis. Since Fe is capped on both sides by Au one obtains a nearly symmetric quantum-well structure.The Au(100) substrate was electropolished (using a cyanide-based method), sputtered (500 eV Ar+ at + 30' from grazing), and annealed (400'C). It exhibited a bright 5&&20 low-energy electron-diffraction (LEED) pattern, which converted to 1 x 1 at submonolayer Fe cover-age. Fe was evaporated from a miniature electron-beam evap...

Spin-dependent transport in Fe andFe∕Aumultilayers

“…11 The segregation of Au was further supported by low-energy electron diffraction 12 and photoemission studies. 13 For the case of Fe deposited on Au/ Fe/ GaAs͑001͒, however, XPS measurements as a function of the top Fe film thickness indicated that Au does not segregate to the surface of Fe.…”

Theory for Spin-Polarized Oscillations in Nonlinear Optics due to Quantum Well States

“…In particular, thin magnetic films and multilayers exhibit a rich variety of properties not previously found in bulk magnetism such as enhanced or reduced moments [2], oscillatory exchange coupling through nonmagnetic spacers [3][4][5], giant magnetoresistance [6,7], and the reorientation of the magnetic easy axis upon thickness and temperature variation [8][9][10][11]. Especially the observation of spin-polarized quantum well states (QWS) [12][13][14][15] in Cu/Co (001) has attracted a great deal of attention. It has become clear that quantum well states are indeed responsible for the important oscillatory behavior of the exchange coupling of ferromagnetic thin films via nonmagnetic spacers [16,17].…”

“…It has become clear that quantum well states are indeed responsible for the important oscillatory behavior of the exchange coupling of ferromagnetic thin films via nonmagnetic spacers [16,17]. Presently mainly photoemission (PE) and inverse photoemission (IPE) [12][13][14][15] have been used to identify QWS effects. Very recently a possible connection between thickness dependent changes in NOLIMOKE and QWS [18] has been proposed.…”

Energy functional dependence of exchange coupling and magnetic properties ofFe∕Nbmultilayers

“…[27], energy E shows oscillation as a function of N. Since the density of states (DOS) for this case varies as E 1 2 , it will also show oscillation as a function of N at Fermi level. The period of oscillations can be predicted by analyzing the peak positions of QW states in the electronic density of states [25,27]. In Fig.…”

“…Several models [5,10,25,26] have been presented to explain the period of oscillations of the IEC. The RKKY and QW models express the period in terms of the nesting vectors at the Fermi surface.…”