Magnetism of Fe films grown on Co(100) studied by spin-resolved Fe $3s$ photoemission

The magnetic properties of fcc Fe films grown on fcc Co(100) have been studied by means of spin-resolved Fe $3s$ core-level photoemission and characteristics of the measured spin-resolved $3s$ spectra for fcc Fe films have been investigated. The spin-resolved $3s$ spectra measured on 3.9 and 6.6 monolayer (ML) fcc Fe films are similar in spectral shape. The $3s$ majority-spin spectra for these fcc Fe films show weaker intensity on the high-binding-energy side than the spectrum previously reported for bulk bcc Fe. The spin-resolved $3s$ spectra for the fcc Fe films are analyzed by cluster model calculation consisting of four Fe atoms. In the analysis by the cluster model calculation, effects of the interatomic configuration interaction on the spin-resolved $3s$ spectra for fcc Fe films are discussed. Itinerancy of $3d$ electrons is found to be an important factor in describing the spin-resolved Fe $3s$ spectra. The $z$ spin momentum estimated by the cluster calculation indicates that both the Fe films are in a high-spin ferromagnetic state near the surface. On the other hand, the spin polarization at the background in the spectrum for the 6.6 ML Fe film is much smaller than that for the 3.9 ML film. This variation of the background spin polarization indicates that the magnetic moment averaged up to deeper layers of Fe film is suppressed in the 6.6 ML film.

Figure 1

The raw Fe $3s$ SRPES spectra for (a) 3.9 and (b) 6.6 ML Fe on Co(100). Upward and downward triangles show the majority- and minority-spin spectra, respectively. The Shirley backgrounds are also indicated by the dotted lines. The peak in the minority-spin spectrum for 3.9 (6.6) ML Fe is marked with $A\left(A^{\prime }\right)$. The insets in (a) and (b) show the structures and ferromagnetic (FM) layers in the corresponding thickness regions. The fct in the insets indicates the tetragonally distorted fcc structure. In region II, the ferromagnetic order exists also in the two layers at the interface as well as the two topmost layers shown in the inset of (b). (c) and (d) show the spin polarizations corresponding to the SRPES spectra in (a) and (b), respectively.

Figure 2

(Color online) The Fe $3s$ SRPES spectra for 3.9 and 6.6 ML Fe on Co(100), in which the Shirley backgrounds are subtracted from the raw spectra. Upward and downward triangles show the majority- and minority-spin spectra, respectively. The peak in the minority-spin spectrum for 3.9 (6.6) ML Fe is marked with $A\left(A^{\prime }\right)$ and the peak in the majority-spin spectrum for 3.9 ML Fe is marked with $B$. The SRPES spectra of the two Fe thin films are superimposed in the inset. The SRPES spectra for 3.9 and 6.6 ML Fe are shown by red and black triangles, respectively.

Figure 3

The configuration ${(5,5,5,4)}_{\uparrow },{(2,2,2,3)}_{\downarrow }$ in the four-atom cluster model.

Figure 4

The Fe $3s$ SRPES spectra for (a) 3.9 and (b) 6.6 ML Fe on Co(100), shown in Fig. 2, are compared to the calculated spectra. Upward and downward triangles indicate the observed majority- and minority-spin spectra. The solid lines in (a) and (b) show the Fe $3s$ SRPES spectra calculated using the parameters listed in Table . The peak in the minority-spin spectrum for 3.9 (6.6) ML Fe is marked with $A\left(A^{\prime }\right)$ and the peak in the majority-spin spectrum for 3.9 ML Fe is marked with $B$. In the majority-spin spectrum for 3.9 ML Fe, the spectral structure on the high-binding-energy side of peak $B$ is denoted by $C$.

Figure 5

(Color online) The dependences of the $3s$ SRPES spectrum on the parameters $⟨S_z⟩$, $⟨n_d⟩$, $t$, and $J$ are examined by the calculation using the four-atom cluster model. The parameters except for (a) $⟨S_z⟩$, (b) $⟨n_d⟩$, (c) $t$, or (d) $J$ are fixed at the values in the calculation for 3.9 ML Fe. The calculated majority- and minority-spin spectra are shown by the solid and broken lines, respectively. The red curves indicate the $3s$ SRPES spectrum calculated from the parameters for 3.9 ML Fe. $A$ and $B$ with bars denote the peaks in the majority- and minority-spin spectra calculated from the parameters for 3.9 ML Fe, respectively. $C$ with dotted bar represents the spectral structure on the high-binding-energy side of peak $B$ in the majority-spin spectrum calculated from the parameters for 3.9 ML Fe. Also in the spectra except for the calculated spectrum of 3.9 ML Fe shown by the red curves, the peaks corresponding to $A$ and $B$ are marked with bars, and the peaks corresponding to $C$ are marked with dotted bars.

Figure 6

The configurations (a) ${(5,5,5,5)}_{\uparrow },{(2,2,3,3)}_{\downarrow }$ and (b) ${(5,5,5,4)}_{\uparrow },{(2,2,3,4)}_{\downarrow }$ and ${(5,5,5,4)}_{\uparrow },{(2,3,3,3)}_{\downarrow }$. The configurations shown in (a) and (b) bring the Coulomb energy among the $3d$ electrons to the minimum for $⟨S_z⟩=1.25$ and 1.00 with $⟨n_d⟩=7.5$, respectively.