Fe was epitaxially grown on an atomically flat GaAs(00 I) surface with a (2 x 6) or a (4 x 2) surface reconstruction. This films are ferromagnetic at room temperature with 100% remanence along the easy direction for a nominal Fe coverage of 3.6 ML and above, Mossbauer and superconducting-quantum-interference-device (SQUID) measurements have shown, that even the first monolayers have the full bulk moment of Fe. In order to study the onset of ferromagnetism the Curie temperature T-C was measured for film thicknesses between 2.8 and 3.6ML, using ac Magneto-optical Kerr effect (ac MOKE). Tc decreases with decreasing film thickness and vanishes at about 2.5ML, which can be interpreted as a percolation effect. The in-plane anisotropy of Fe and FeCo alloys on GaAs(00 1) consists of an uniaxial (K-U) and a fourfold anisotropy (K-1). The uniaxial anisotropy is in both cases a pure interface effect, while the effective fourfold anisotropy constant can be separated into an interface (K-1(int)) and a volume term (K-1(vol)). Both K-1(int) and K-1(vol) of FeCo have the opposite sign of K-1(int) and K-1(vol) of Fe. Upon increasing film thickness, this leads to a change of sign of the effective fourfold anisotropy constant at about 6ML from negative to positive for Fe and from positive to negative for FeCo. The strong uniaxial anisotropy of Fe on GaAs(001) is preserved in patterned Fe dots with 200nm diameter, 1.4nm height and 500nm period, which leads to a remanence of 100% along the easy direction.

Epitaxial Fe34Co66 films in a thickness range from 3 to 100 monolayers (MLs) were grown by molecular beam epitaxy on GaAs(001) at room temperature. The growth was characterized by reflection high energy electron diffraction and x-ray diffraction. The magnetic properties were investigated by alternating gradient magnetometry magneto-optic Kerr effect, and superconducting quantum interference device magnetometry. The films show a strong interface-induced uniaxial in-plane anisotropy with the easy axis along [110]. In addition, the fourfold anisotropy coefficient changes sign around 6 ML i.e., the easy axis of the fourfold anisotropy switches from 〈110〉 to 〈100〉 with decreasing thickness.

Epitaxial Fe films were grown on Ga-terminated GaAs(001) surfaces by molecular beam epitaxy. Samples with constant Fe thickness as well as step patterned Fe films have been studied. In-plane magnetic anisotropy energies were determined from hysteresis loops measured by alternating gradient magnetometry and magneto-optic Kerr effect. A superposition of anisotropies with fourfold and uniaxial symmetry was found in all films. From the linear variation of both contributions with the inverse Fe thickness, the volume and the interface term are determined. The fourfold anisotropy constant of the Fe/GaAs(001) interface amounts to −(1.41±0.2)×10−2erg/cm2. As a consequence, the easy and hard directions of the fourfold term are rotated by 45° below 6ML. The uniaxial anisotropy turns out to be a pure interface term originating exclusively from the Fe/GaAs interface. The huge anisotropy constant, KUFe/GaAs=(1.2±0.2)×10−1erg/cm2, produces an in-plane anisotropy field up to 2kOe.

In-plane fourfold and uniaxial magnetic anisotropies were studied in Fe films epitaxially grown on vicinal Ag(001) and Au(001) surfaces, which were prepared by molecular beam epitaxy on miscut GaAs(001) substrates. The effective fourfold and uniaxial anisotropy constants, K1eff and Kueff, which are determined from magnetisation curves measured with the magneto-optic Kerr effect, are linear functions of the inverse Fe layer thickness. The fourfold anisotropy shows a rotation of the easy and hard axes by 45° below a critical thickness of 6–7 ML. The uniaxial term is mainly an interface contribution. We find that the orientation of the uniaxial easy axis depends on the Fe thickness. In thinner films (tFe⩽20 ML) it is oriented perpendicular to the step edges, i.e., parallel to Fe[100]. This excludes shape anisotropy as the main mechanism. Above a critical thickness the uniaxial easy axis is aligned parallel to the step edges, i.e., along Fe[010]. This step-induced uniaxial anisotropy may be due to modified electronic states and to strain from the large vertical misfit at the steps.

Future ‘magneto-electronics’ exploiting the spin of the electron in addition to its charge will require the injection of spin-polarized electrons from a ferromagnetic metal into a semiconductor. To this purpose an attempt has been made in the present study to avoid the formation of a non-magnetic interface phase or ‘magnetically dead layers’ which have been found in the past in Fe films epitaxially grown on GaAs(0 0 1). Fe(0 0 1) films were grown by molecular beam epitaxy and magnetron sputtering on As depleted GaAs(0 0 1) surfaces held at room temperature. Very good epitaxial growth is achieved by both deposition methods. MBE grown ultrathin films show an enhanced ground state net magnetization and the full bulk magnetic moments at the Fe/GaAs interface in contrast to previous reports. This might be an important step towards semiconductor devices using spin polarized electron transport. The in-plane magnetic anisotropy of the films generally consists of a fourfold and a uniaxial term. At 7 monolayer thickness only a strong uniaxial contribution is observed which is supposed to result from the intrinsic anisotropy of the dangling bonds at the GaAs(0 0 1) surface. This could also be a useful property for future memory or switching applications.

We studied the growth and magnetic properties of ultrathin Fe(001) films on Au(001) buffer layers grown by molecular-beam epitaxy on MgO(001) single crystals. Epitaxial growth could be achieved by use of a Cr seed layer. Epitaxial quality and surface structure were verified in situ by low-energy and reflection high-energy electron diffraction and scanning tunneling microscopy (STM). Magnetic anisotropy of Fe films in the range of 3–155 monolayers (ML) was determined by alternating gradient magnetometry, superconducting quantum interference device, and magneto-optic Kerr effect. The spontaneous magnetization was always in the film plane. Below a critical thickness of 7.3±0.7 ML we observe a rotation of the cubic easy axes by 45° from the 〈100〉 to the 〈110〉 directions within the film plane. This spin reorientation transition is equivalent to a sign reversal of an effective fourth order anisotropy constant K1eff. In addition, a uniaxial in-plane anisotropy is observed, which may be attributed to the step structure of the samples obtained from STM images.

We have investigated the growth and magnetic properties of ultrathin Fe films on Au(OO 1). The films used for magnetometry have been prepared by MBE on pre-annealed MgO(OOI) single crystals. Epitaxial growth of the 300-500 monolayer Au buffer layer as well as of the Fe films in the monolayer range could be achieved by use of a Cr seed layer. Epitaxial quality and surface structure was controlled in situ by electron diffraction (LEED, rumED) and ex situ by STM and AFM. Comparative growth studies were perfonned for Fe-films on a Au single crystal substrate by in situ STM and ion scattering spectroscopy. We have investigated the magnetic anisotropy of Fe films in the range 3-50 monolayers with alternating gradient magnetometry (AGM). We find a uniaxial out-of-plane contribution of the surface anisotropy which promotes a spontaneous out-of-plane magnetization for films < 2.1 monolayers. Additionally, we report on a fourfold in-plane surface anisotropy, which leads to a switching of the in-plane easy axes into the [11 OJ and [11 DJ directions for the 3 and 5 monolayer Fe films. We discuss these anisotropy phenomena in context with the breaking of translational symmetry at the interface.

A magnetic interface anisotropy with the easy axis perpendicular to the film plane was found for ultrathin epitaxial Fe films on Au(111) and for Fe/Au sputtered multilayers (0.5 ML less-than-or-equal-to t(Fe) less-than-or-equal-to 50 ML). The interface anisotropy field, H(S), is shown to depend on film structure (determined by growth mode and growth conditions) and the degree of intermixing introduced by controlled co-deposition of Fe and Au.

Magnetic properties of ultrathin Fe and Fe60Au40 alloy films on Au(111) were studied by SQUID magnetometry and conversion electron Mössbauer spectroscopy. In order to get information on the influence of interdiffusion, iron films with thin alloy zones at the interfaces to Au have been prepared by co-evaporation of iron and gold and compared with iron films with presumably sharp interfaces. It was found that the presence of an 0.5 ML (mass coverage in monolayer) alloy zone reduces the effective magnetic interface anisotropy field and affects the growth mode of a subsequently deposited iron film such that the film is more sensitive to annealing. Groundstate magnetic moments and hyperfine fields are significantly enhanced in Fe/Au(111) (tFe ≤ 4 ML) and Fe60u40 films, compared to bulk Fe.