Effects on magnetic and optical properties of perpendicular electric fields up to 1 MV/m were studied on thin ferromagnetic films of MnAs grown epitaxially on GaAs(001) substrates. Film thicknesses were 20, 50, 100 and 200 nm, With positive electric field corresponding to positive polarity of the MnAs film with respect to the GaAs substrate, it was found that at a field magnitude of 1 MV/m: (a) the magnetizations of the 20 and 50 nm films decreased by 3.5 and I percent, respectively, under both positive and negative fields as measured by vibrating sample magnetometry; (b) the magnetooptical Kerr effect (MOKE) of the 20 nm samples decreased by 3.5 percent in negative field but was unchanged by positive field; (c) the index of refraction of the 20 nm films determined by ellipsometry increased by 1 percent in positive field but was unchanged by negative field, No effects were found in thicker films, indicating the observed effects arise from the region of MnAs near the substrate. The MOKE signal of the 20 nm films has a power law dependence on electric field with an exponent of 0.36 with a standard deviation of 0.04. The intensity of the (10-10) x-ray diffraction peak from the ferromagnetic, hexagonal MnAs phase of a 20 nm film decreased by 5 percent in both positive and negative fields of 1 MV/m; however, there was no corresponding increase in the nonmagnetic, orthorhombic phase.

We have studied the magnetic, magneto-optic, and structural properties of Mn1−xNixAs films grown by molecular beam epitaxy on GaAs(001). The compositions are x=0.1, 0.2, 0.3 with a thickness about 100 nm. In the magneto-optical Kerr effect, Mn0.9Ni0.1As displays distinct longitudinal and polar Kerr rotations. At x=0.2, the effects are smaller, and are undetectable at x=0.3. Magnetometry yields a linear dependence of magnetization on Ni concentration. X-ray diffraction shows a gradual transition from hexagonal to orthorhombic structure. In contrast, bulk Mn1−xNixAs alloys at 300 K are paramagnetic and orthorhombic for x>0.02 and transform to an hexagonal phase at x=0.22.

We have created a new class of epitaxial magnetic multilayers, consisting of ferromagnetic MnAs and nonmagnetic NiAs, on (001)GaAs substrates by molecular beam epitaxy. It was found that the growth plane of MnAs and NiAs is the (1100) of hexagonal crystal structure, and that the easy axis of magnetization of MnAs is in-plane, along the [1120] axis, which is parallel to the [110] of GaAs. Multi-stepped magnetic hysteresis are controllably realized, making this material promising for the application to multi-level non-volatile recording on semiconductors.

Epitaxial MnAs films on GaAs(001) in the thickness range 20–200 nm were studied. Using ordinary and extraordinary Hall effect data to determine the field required for perpendicular saturation and saturation magnetizations reported elsewhere, we determined the shape anisotropy constant in the basal plane of the hexagonal structure to be 3.7(0.6)×105 erg/cm3 and the surface anisotropy constant to be −1.3(0.4) erg/cm2. The negative sign indicates thin enough films will be perpendicularly magnetized. By magnetic force microscopy of a 100 nm film we found stripe domains with 180° Bloch walls, thereby avoiding the hard c axis. The widths of the domains and the walls are 4.0(0.3) μm and 95(6) nm, respectively. In magnetoresistance, we observed behavior similar to other ferromagnets, namely peaks centered around the positive and negative coercive fields, and at fields beyond the coercive field a linear dependence on magnetic field. The electrical resistance showed rapid increase with temperature beginning about 5° below the Curie temperature (40 °C) caused by the change in crystal structure from hexagonal to orthorhombic. The resistivities are, respectively, 300(24) and 375(30) μΩ cm. Comparison with bulk values indicates the large lower temperature value is partly due to the presence of some orthorhombic phase observed in x-ray studies.

We have studied epitaxial orientations and template effects in molecular beam epitaxy (MBE) of ferromagnetic MnAs thin films on (001) GaAs substrates. The MBE-grown MnAs thin films take two different epitaxial orientations, [1100] (type-A) and [1101] (type-B), depending on the surface reconstruction and one monolayer template formation on (001) GaAs surfaces just prior to the growth of MnAs. The easy axis of the magnetization in type-A and type-B MnAs films is along the [110] and the [110] of GaAs, respectively, 90° different with respect to the GaAs substrates. Furthermore, when a very thin epitaxial ErAs template layer was formed on c(4 × 4) GaAs and then MnAs was grown, the growth direction of the MnAs was found to be [1102], and no strong magnetic anisotropy was observed within the film plane. These results indicate the importance of the first few monolayers and starting surface stoichiometry to control the epitaxial orientation and magnetic properties of the epitaxial ferromagnetic MnAs thin films.

We have studied structural and magnetic properties of epitaxial MnAs thin films with various thicknesses (L=1.0–200 nm) on GaAs substrates. The MnAs thin films were grown at 200–250 °C on an As-rich disordered c(4×4) (001) GaAs surface by molecular-beam epitaxy (MBE). The growth direction of the MnAs was found to be along the [1̄100] axis of the hexagonal unit cell. X-ray spectra of the MnAs at room temperature have two peaks, indicating that the present MBE-grown MnAs films consist of the hexagonal ferromagnetic phase and orthorhombic paramagnetic phase. Magnetization measurements revealed that the MnAs thin films have perfectly square hysteresis characteristics with relatively high remnant magnetization Mr=300–567 emu/cm3 and low coercive field Hc=65–926 Oe, compared with those of epitaxial MnGa and MnAl thin films reported previously.

We have successfully grown single-crystalline ferromagnetic MnAs thin films on (001) GaAs substrates by molecular beam epitaxy. By reflection high energy electron diffraction and x-ray measurements, the growth direction of the MnAs thin films was found to be [100] on (001) GaAs, and the epitaxial relationship was [0001] MnAs //[10] GaAs and [110] MnAs // [110] GaAs. Magnetization measurements at room temperature have revealed that the epitaxial MnAs thin films have strong magnetic anisotropy, and that the easy magnetization direction is in-plane, along the [110] axis of the MnAs thin films which is parallel to the [110] axis of the GaAs substrate, with almost perfect square hysteresis loops, relatively high remanent magnetization, and low coercive field.

We have studied template effects in molecular beam epitaxy (MBE) of ferromagnetic MnAs thin films on (001) GaAs substrates. When As2 flux was first supplied without Mn flux on the (001) GaAs prior to the MnAs growth, the surface reconstruction was disordered c(4×4), a more As-rich surface than c(4×4). The growth direction of the MnAs thin film grown on this surface is [1̄100] and the easy magnetization axis was found to be along the [1̄1̄20] of MnAs and the [110] of GaAs. In contrast, when one monolayer of Mn was first deposited on the c(4×4) GaAs surface and then As2 flux was supplied to grow MnAs, the growth direction of the MnAs thin film was found to be mainly [1̄101], and the easy magnetization axis was along the [1̄1̄20] of MnAs and the [1̄10] of GaAs, 90° different with respect to the substrate. These results indicate the importance of the very first monolayer in controlling the epitaxial orientation and magnetic properties of epitaxial ferromagnetic MnAs thin films.

A significant advantage of photoelectron extended x-ray absorption fine structure (PEXAFS) is that it has chemical sensitivity afforded by measuring chemically shifted photopeaks as functions of photon energy. The structures responsible for the different peaks may be studied. In addition other features of the photoelectron spectrum may be used. We have studied evaporated, polycrystalline aluminum films exposed to oxygen and obtained PEXAFS data using the unshifted Al 2p photopeak, the chemically shifted (2.4-eV) photopeak, and the bulk and surface plasmon loss peaks. At low oxygen exposures and also using the unshifted peak at 1000-L exposure the Al–O and Al–Al separations are, respectively, 1.76(4) and 3.00(5) Å. The shifted peak yields distances larger by 0.04(1) and 0.06(3) Å. Nearest-neighbor oxygen is found about the unshifted aluminum atoms, which suggests a reinterpretation of earlier surface EXAFS using O 1s photoabsorption. We propose this dissolved oxygen is in or near threefold sites in (111) planes.

Presentation des resultats experimentaux obtenus sur des structures de surface des couches d'aluminium polycristallines evaporees, exposees a environ 25L d'oxygene a temperature ambiante

Photoemission EXAFS has chemical sensitivity not available from other methods. CIS spectra were obtained on Al films after oxidation. Spin polarized EXAFS was used to study magnetic structure. Preliminary measurements were made on the antiferromagnet MnTe above and below the Neel point. (DLC)

We report the first definitive measurements of extended x-ray absorption fine structure (EXAFS) made by monitoring the direct photoelectron emission as a function of photon energy. We have measured EXAFS associated with the Mn $3p$ and F $2s$ core levels in evaporated films of Mn${\mathrm{F}}_{2}$ and found good agreement with bulk transmission EXAFS associated with the Mn $1s$ level. Photoelectron EXAFS makes possible surface-sensitive structural determinations using vacuum uv radiation on a virtually unlimited range of systems.

The first definitive measurements of EXAFS by monitoring the direct photoelectron emission as a function of photon energy have been made using the Mn 3p and F 2s core levels in evaporated films of MnF2 [1,2]. Good agreement is found with bulk transmission EXAFS obtained with the Mn Is level. This development is important because: (1) Almost all elements have suitable core levels of low binding energy. (2) Since photopeaks from adjacent core levels do not cross as the photon energy is varied, the limitation imposed on other EXAFS techniques by this interference is removed. Auger electrons, which have fixed kinetic energies and so can cross photo-peaks, will generally have low energies if they originate from the outer core levels and be unlikely to appear in the EXAFS region of kinetic energies, i. e., in excess of about 50 eV. (3) VUV light is used, which greatly extends the useable range of photon energies. (4) More than one element in a solid may be studied with the same monochromator.

We describe a new beam line at the ACO storage ring for solid state photoelectron spectorscopy incorporating a 1 m focal length toroidal grating monochromator for the photon energy range 6 eV to 120 eV custom-built by Jobin-Yvon Instruments S.A. Test results for the TGM with laboratory line light sources are reported as well as performance data with synchrotron radiation.