A brief review of the state of the art in the field of surface, interface and thin-film magnetism is presented.

The formation of magnetic domains in thin epitaxial Co/Au(111) films is investigated by spin-polarized scanning electron microscopy. Three-monolayer films are shown to decay into out-of-plane domains of micrometer size. The transition from out-of-plane to in-plane magnetization at a crossover thickness of 4.5 layers is followed by imaging the domains, and the transition is shown to occur as a continuous rotation of the magnetization. The domain size in field-free-grown perpendicular films depends linearly on film thickness. From high-resolution line scans across magnetization reversals we determine the resolution in magnetic imaging to be better than 40 nm.

A brief discussion of the resonant magnetic scattering process is given. Results from recent studies of thin Fe films and Fe/Gd multilayers are used as examples to demonstrate the information can be obtained and the unique features of this technique: large resonant enhancement, sensitivity to magnitization, elemental specificity, and tunability of the penetration depth. Comparison is made with related techniques: magneto-optical Kerr effect, Faraday effect, and magnetic circular dichroism.

We report on a novel promising technique for the investigation of magnetic structures at surfaces at high spatial resolution, ultimately down to the atomic scale. This technique is based on the observation of vacuum tunneling of spin-polarized electrons by means of a scanning tunneling microscope (STM). We discuss appropriate probe tips for the spin-polarized STM (SPSTM) and describe initial experimental results. We further focus on the information obtained by SPSTM. Finally, the perspectives of SPSTM will be discussed.

Spin polarized photoemission is used to study the magnetic states associated with the clean iron (001) surface. These studies reveal evidence for a minority spin surface state in agreement with a first principles calculation. Studies of the same surface with silver and chromium epitaxial overlayers reveal evidence for interface states derived from this state found on the clean surface. In the case of the silver overlayer the binding energy of the new state is found to be dependent on the layer by layer thickness of the overlayer. With chromium overlayers the binding energy for the same interface state does not show the same thickness dependence. However a second interface state is observed immediately below the Fermi level. These changes in the interfacial electronic structure have implications for any modelling of magnetic coupling in multilayers dependent on the magnetic properties of the interface.

The spin resolved electronic structure of ultra-thin Fe films on Cu(100) was investigated using spin polarized angle resolved photoemission spectroscopy. All exchange splitting of the Fe ∆s band of 2.5 eV is observed for photon energies between 20 and 30 eV. ∆ peak at 6 eV binding energy which has been previously identified as a many-electron resonance was observed only after contamination of the films with oxygen. In addition, the spin dependent attenuation lengths for electrons in Fe were measured at 11, 19, and 40 eV above Ef. The attenuation length for the minority spin electrons was found to be shorter than that of the majority spin electrons. The difference between the two attenuation lengths was shown to increase at low energy. Short attenuation lengths of ≃3 monolayer were measured at II eV. The large increase of the attenuation length at low energy which is expected from the “universal curve” is not observed in Fe.

We summarize results of our recent theoretical studies of spin dependent scattering of electrons from ferromagnetic surfaces. We obtain an excellent account of both the energy and angle variation of the exchange asymmetry reported by Waller and Gradmann in their SPLEED study of the Fe(110) surface, and of spin dependent asymmetries in the transmission of photoelectrons through an ultra thin film of Fe on Cu(100). Potentials supplied by Fu and Freeman enable us to account for the data, with use of ground state potentials generated by ab initio methods.

The magnetism and the electronic structure of fcc Co films epitaxially grown on Cu(100) was investigated by spin polarized electron energy loss spectroscopy. Films above 2 atomic layers thickness show ferromagnetic order above room temperature with the magnetization in the plane. An exchange splitting of 0.8 eV and a Stoner gap of 300 meV is found. Films thinner than 1.6 layers do not show remanent magnetization above 80 K. No evidence for enhanced moments in monolayer films is found.

Local d-magnetic moments of the Pt interlayer in Pt/Co multilayered structures (4 ÅCo + X ÅPt, X=9,19,23,30,40) have been investigated theoretically and experimentally by circular magnetic x-ray dichroism studies.

It has been found that a significant Pt polarization is induced, which contributes by about 13% to the total magnetization. The experimental findings of the average Pt moments agree well with the theoretical expectations indicating the existence of a longrange exchange coupling through the Pt layer.

We present data from low-energy He+ ion scattering off a magnetized Fe(110) surface where we monitored the circular polarization of the light emitted from particles neutralized into excited states. We investigated the dependence on incident energy, incident angle and magnetization for a singlet and a triplet transition. As expected, there is no dependence on magnetization for the singlet state, but for the triplet transition we observed a difference in the circular polarization of as high as 32% when changing the direction of the magnetization.

Epitaxial growth of rare-earth superlattices is demonstrated to have opened important new areas of research on magnetic materials. The propagation magnetic order through non-magnetic elements, including its range and anisotropy, has been studied. The importance of magnetostriction in determining the phase diagram is demonstrated by the changes induced by epitaxial clamping. The crystallinity of epitaxial superlattices provides the opportunity to study interfacial magnetism by conventional x-ray and neutron scattering methods.

Fine structure is observed in the photoemission of Gd and Tb 5p levels as a result of multiplet splitting. These splittings are the consequence of different J final states that occur as a result of interactions with partly filled 4f and/or 5d levels.

Using polarized-neutron reflectivity, one can determine the layer-averaged magnetic structure of films and multilayers with exquisite precision. By employing the closely related phenomenon of grazing-angle diffraction, it is possible to obtain information about the in-plane structure in interfacial layers some tens of Ångstroms thick. We have used polarized-beam methods to study the Y/Gd interface using both reflectivity and grazingangle diffraction and discuss the status of these experiments.

We report structural and magnetic X-ray scattering measurements of a 2000Å thick Dy film, sandwiched by LaF3 films on a GaAs(111) substrate. The structure was grow by molecular beam epitaxy with the c-axis of the Dy parallel to the LaF3 c-axis and GaAs[111] axis. For the magnetic X-ray scattering, we used a polarization analyzer and an X-ray energy near the Dy L111 absorption edge. ∆t this energy there is a resonant enhancement in the magnetic scattering intensity, and we obtained ≃-50 counts per second in the magnetic diffraction peaks.

Between 85 and 179K, bulk Dy forms a helical antiferromagnetic structure, and below 85K, it transforms into a ferromagnet. We find that the c-axis lattice constant of the Dy film has a similar temperature dependence to bulk Dy from room temperature to about 110K, but below this, the film behaves differently from bulk and is strained. The temperature dependence of the turn-angle in the helical antiferromagnetic state is similar to bulk, although a weaker dependence is observed below ∼1 10K due to magnetoelastic effects. Surprisingly, the magnetic coherence length (≃310Å) is significantly shorter than the structural coherence length (≃730Å). The transition to ferromagnetic ordering at 86K exhibits temperature hysteresis as is evident in the structural and magnetic X-ray data and in SQUID magnetometry data. We believe this hysteresis arises from a combination of the strain-energy barrier accompanying the transition and magnetic inhomogeneities in the film.

We prepared Fe/Gd double structured multilayer films (DSMLF's). The Fe/Gd DSMLF has a longer period λl, and it is composed of alternate stacking of two types of Fe/Gd submultilayers with a shorter period λs. One type of Fe/Gd submultilayers has dominant Fe layer magnetization, and the other, dominant Gd layer magnetization. λs was varied in the range from 12 to 100Å, keeping λl to about 250Å. The magnetization of Fe/Gd DSMLF's with λs≦36Å shows a spin-flop in magnetic fields lower than 1k0e at room temperature. The compensation temperature Tcomp was found to decrease with increasing λs. Tcomp crosses room temperature at λs=24Å, and then the spinflop field Hsf at room temperature takes a minimum value of the order of a few tens oersteds. Thus, we show that Hsf at room temperature can easily be tuned to a desired value by varying λs. Longitudinal (pl) and transverse (pt) magnetoresistances show a crossover, depending on the angle between directions of the electric current and of the Fe layer magnetization.

By means of light scattering from spin waves and magnetooptical Kerr measurements we investigated the exchange interaction of two Fe films across a Cr film as a function of the Cr thickness dCr.

Using good quality epitaxial samples with a special wedge geometry of the interspacer we observed up to four full periods of the long range oscillations of the exchange, including its ferromagnetic parts. At room temperatures the damping of the oscillations does not follow the d-2Crpendence predicted by zero-temperature RKKY-type theory.

After a special e-beam treatment of the samples a short-range oscillation with a period around a lattice constant of Cr are discovered. The value of coupling in the maximum in this case shows considerable temperature dependence.

The analysis of domain patterns and M(H) curves reveals the existence of a noncollinear interaction, which causes a configuration where the magnetizations of two Fe films are perpendicular to each other.

We show that oscillatory interlayer exchange coupling of thin magnetic layers through metals is a general phenomenon present in almost all the transition and noble metals. Surprisingly the period of the oscillations is approximately the same, about 10Å, in all these metals with the sole exception of Cr for which the period is significantly longer. The strength of the coupling varies systematically throughout the 3d, 4d and 5d transition metals increasing exponentially along each of the transition metal periods and increasing from the 5d to 4d to 3d periods. These results appear to be inconsistent with simple Ruderman-Kittel-Kasuya-Yosida (RKKY) based models.

The temperature dependence of the magnetic hyperfine (hf.) fields near the interfaces in epitaxial Fe/Cr and partly epitaxial Fe/Gd bilayers were measured using 57Fe Conversion Electron Mössbauer Spectroscopy (CEMS). It was found that the Fe-Cr magnetic interaction extends only up to the second Fe-neighbor at the Fe/Cr interface, whereas the interaction range at the Fe/Gd interface is four times larger. For comparison the hf. fields and magnetic moments for Fe/Cr multilayers were obtained performing LMTO (Linear Muffin Tin Orbital) band structure calculations. The Néel temperature of a thin Cr-interlayer in a Fe/Cr/Fe sandwich structure was determined in dependence of the Cr-layer thickness.

We report results of X-ray diffractometry and magnetic measurements performed on Ag/Ni superlattices prepared by triode dc-sputtering. The X-ray results suggest structural coherence and interface sharpness whatever the thickness of the elemental layers with (111) textures for both Ag and Ni. Magnetization measurements confirm the existence of sharp interfaces. They also indicate that the magnetic moments preferentially lie in the plane of the layers whatever the Ag or Ni thicknesses. We also present evidence of the oscillatory character of the magnetic coupling of the Ni layers through the non-magnetic Ag layers, which correlates with both magnetoresistance and low-angle neutron diffraction experiments.

The effect of layer structure perturbations on antiferromagnetic coupling in Fe-Cr-Fe trilayer systems is investigated. By varying the sputtering pressure, the layer structure of Fe-Cr-Fe trilayers is systematically altered, as indicated by changes in the low angle superlattice spectra of multilayers fabricated under identical conditions. The effect of topographic roughness is investigated by fabricating identical trilayers on Cr buffer layers of different thickness. Scanning tunneling microscopy is used to measure surface roughness. In each case the saturation field is measured as a function of Cr interlayer thickness by means of tapered Cr interlayer structures in which the thickness of the spacer varies linearly from 0 to 28 Å upon a single substrate. Antiferromagnetic coupling is measured locally by means of the magneto-optic Kerr effect. Results show that although the coupling is diminished by structural perturbations, it is a remarkably robust effect which persists even in instances of poor layer structure.