Three series of nanostructured, μm thick, Co/Ag composite thin films (13, 39 and 61 volume % Co) were produced by dc magnetron sputtering at various substrate temperatures (100–600°C) to determine their magnetic properties and characterize the microstructure. The films were found to be composed of finely dispersed Ag and Co particles. The film surfaces become rougher as the substrate temperature was increased. The crystal lattice structure of the Co was found to be fcc except at the lower substrate temperatures (<300°C) in the 61 volume % films where it was found to be a mixture of fcc and some hcp. The average diffracting particle size of both the Co and Ag rich phases increase with substrate temperature. The magnetic coercivity of the films reached a maximum value when the Co particle size was between 100–150Å.

It is important to control the internal stress of the deposited film because the magnetic tape is becoming thinner for attaining higher recording density per volume. Kr gas was used as the working gas in the facing targets sputtering (FTS) system for depositing Co-Cr films. Kr gas has the larger ionization cross section and atomic mass than those of Ar, Co and Cr, so that Kr gas could make stable discharge at lower pressure and the recoiling of Kr atoms on the surface of the Co-Cr target was more effectively suppressed. Therefore, Kr ions seem to be more advantageous as working gas than Ar ions which are the most common working gas. The FTS method with Kr ions could deposit the stress-free Co-Cr films with good crystallinity. Actually, Δθ50 and (Mr/Ms) of Co79Cr21 films deposited on Si wafer by Kr ion sputtering in the pressure range of 10–4 ∼ 5×10−−5 Torr were as small as 4% and 0.1, respectively. The colpressive stress of 1500Å-thick Co79Cr21 films was as small as 108 dyne/cm2, of which the value was smaller than 10% of that by Ar ion sputtering. Therefore, the combination of the FTS method and Kr gas seems to be very convenient for solving the problem of the internal stress.

Epitaxial films of ferromagnetic τMnAl with perpendicular magnetization have been grown on {100}AlAs/GaAs substrates by molecular beam epitaxy. A multistep growth procedure involving the formation of a template followed by codeposition and subsequent annealing yields thin epitaxial τMnA1 films that exhibit the extraordinary Hall effect with nearly ideal hysteretic characteristics.

We have observed an ordered structure in Zn0.5Fe0.5Se epilayers grown on (001) InP substrates using transmission electron microscopy. The ordered structure of Zn0.5Fe0.5Se has Fe atoms occupying the (0,0,0) and (½, ½, 0) sites and Zn atoms occupying the (0, ½, ½) and (½, 0, ½) sites in the zinc-blende unit cell. Ordering is observed in both electron diffraction patterns and cross-sectional high-resolution lattice images along the < 100 > and < 110 > directions. This ordered structure consists of alternating ZnSe and FeSe monolayers along the < 100 > and < 110 > directions. Computer image simulations of the high-resolution images under various thicknesses, and defocusing conditions have been obtained and are compared with those obtained experimentally.

This paper has made an overview on elastic and structural aspects of three distinct superlattices under hydrostatic pressure up to about 8GPa, which were studied by our unique x-ray diffraction technique incorporated with a diamond-anvil cell. They are metallic fcc/fcc Au/Ni, bcc/fcc Mo/Ni, and semiconductive epitaxially-grown PbSe/SnSe superlattices. In their layer-stacking direction, both metallic superlattices show the supermodulus behavior while the semiconductive one doesn't. However, its pressure-driven cubic-to-orthorhombic phase transition, successively taking place in the SnSe and PbSe layers, has been found to significantly shift by stress due to its epitaxial growth.

Fe and Si layers were deposited alternately by using ion beam sputtering apparatus and the relationship between crystal structure and soft magnetic properties of these multi-layered films have been investigated in detail. The clear periodicity of multi-layered films was confirmed even at the thicknesses of Fe and Si layers δFe and δSi as small as 8.5 Å.

The saturation magnetization 4πMs for all Fe layers decreased with decrease of δFe and δSi, and the coercivity Hc of these films took minimum of 1.0 Oe at δFe of 8.5 Å.

Such a significant decrease of 4TEMs may be attributed to the formation of nonmagnetic regions at both side of each Fe layers. The thickness of these nonmagnetic regions may be estimated at approximately 1.5 Å from the measured value of 4flMs. This thickness seems to be very small because it is almost equal to that of one monolayer of bcc α-Fe. The low Hc of the films with δFe and δSi of 8.5 Å may be due to the formation of ultra-fine crystallites in Fe layer by insertion of amorphous Si layer and the direct magnetostatic interaction among Fe layers.

X-ray diffractometry at grazing incidence has been performed upon Nin/Fen multilayers with 6<2n<30mpl (n = no. of monolayers per nn layer, mpl), as a further test that the observed reduction in magnetisation (as n decreases) was not due to interfacial alloying. The results show that the interfaces are terraced to the extent that pinholes occur in the thinner layers. The layers became continuous for modulations 2n>10mpl. Each X-ray scan revealed a series of peaks which corresponded to integer monolayer differences in modulation periodicity. In contrast, interfacial alloying would have produced a broad single peak.

M-H loops were performed on the samples for the range of temperatures 6<T<300K using a vibrating sample magnetometer with the field always applied in the plane of the sample. The sample coercivity was observed to vary with modulation wavelength such that at a modulation of 2n=16mpl it was about a factor of three greater than at either 2n=6mpl or 2n=30mpl. The coercivity peak occurs at a value of n equal to the critical layer thickness for the transformation of the Fe from FCC to BCC. High angle X-ray diffractometry shows an apparent change in planar spacing at the same modulation layer thickness (n=8mpl).

The ratio of remnant magnetisation at low temperature to that at room temperature, RT, was greater than unity for all the samples measured. The ratio increased as the modulation period of the samples decreased. This is consistent with a modulation period dependence of the Curie temperature of the Ni/Fe multilayers.

Magnetic properties of sputtered Ni/Al multilayers have been investigated by vibrating sample magnetometry and ferromagnetic resonance. In these compositionally modulated films (CMFs) the Al ‘spacer’ layer thickness was fixed at 3.5 nm while the total Ni content of each film was held constant at 308 nm. The thickness of the individual Ni layers was varied from 4.8 to 154 nm. The CMFs showed a variety of magnetic characteristics which were dependent on the thickness of the Ni layers. CMFs with Ni layer thickness 30 nm and above showed clear evidence of perpendicular anisotropy. This anisotropy is characterized by low-remanence perpendicular hysteresis loops of the type commonly found in CoCr alloy films. As the Ni layer thickness diminishes the perpendicular anisotropy decreases and is eventually lost. Simultaneously, the CMFs show increasing in-plane remanence, rising to a peak squareness of greater than 0.5 at a Ni layer thickness of 11 nm. As the Ni thickness continues to decrease, the remanence again declines. At Ni thicknesses of a few nm the CMFs become quasi-superparamagnetic. These CMFs do not show a monotonic reduction in saturation magnetization, Ms, with decreasing Ni layer thickness. Instead, both Ms and the coercivity, Hc, pass through a maximum in the region of 40–80 nm Ni layer thickness. FMR measurements were also made on these films. A plot of the effective anisotropy field produces data of a similar form to the Ms versus Ni layer thickness plot, again with a clear maximum. The FMR data also reveals interesting resonances in the films exhibiting perpendicular anisotropy. The presence of satellite resonances adjacent to the principal resonance peaks seems to suggest, in structural terms, a two-phase system as the basis of the observed anisotropy.

A series of epitaxial Co/Cr superlattices has been grown by molecular beam epitaxy. The Cr is in a metastable hcp phase as confirmed by transmission electron microscopy, selected area diffraction, and reflection high energy electron diffraction. The Cr layers are 10Å thick in all samples while the Co layers are varied from 12Å to 40Å. The diffusion between Co and Cr is studied by SQUID magnetometry and indicates step-like interfaces in the best samples. Interfacial sharpness has also been found to be unusually sensitive to Co deposition rates, and in contrast with other superlattice systems, we find that sharper interfaces enhance parallel anisotropy. Hall effect measurements of the saturation field are within 10% of SQUID values. Magnetoresistance at 4.2K is only 1/3% which we believe is a consequence of the high density of states at the Fermi level of hcp Cr.

We demonstrate the growth of epitaxially ordered Cobalt-Chromium (Co-Cr) superlattices by ultrahigh-vacuum deposition techniques. The superlattices, consisting of hcp Co (00.1) and hcp Cr (00.1) layers with their [11.0] crystallographic axes parallel to GaAs [110] have a hexagonal closed packed (hcp) structure with the c-axis normal to the film plane.

Several metallic multilayers with very thin magnetic Co layers display a preferred magnetization perpendicular to the interfaces. There are strong indications that the magnitude of this anisotropy depends critically on details of the microstructure of the multilayers, and especially on the atomic structure of the interfaces. The micro- and nanostructure of Co/Pd and Co/Au multilayers, which exhibit a large difference in lattice parameter (9% and 14% respectively), was studied by conventional transmission electron microscopy (TEM) and high resolution TEM (HREM). The multilayers, grown by vapor deposition, show a columnar structure and have a convex curvature in the growth direction. In Co/Au multilayers also the Au lattice is bent. Misfit dislocations are observed at the interfaces even for Co layers of one atomic layer thickness. Generally the interfaces show atomic roughness, which is more severe for Co/Au than for Co/Pd.

Multilayers of Fe(100)/Ag(100) were grown by MBE and analyzed with in situ RHEED and MÖssbauer spectroscopy. These films had a constant Ag layer thickness of 40 monolayers (ML) and varying Fe layer thicknesses of 3, 6, and 9 ML. Using MÖssbauer spectroscopy the presence of three Fe sites was inferred. From considerations of the hyperflne parameters and the relative intensities of the sextets, we assign one site to the bulk, and one to each interface: Fe on Ag and Ag on Fe. We believe that one explanation of this is differing tetragonal distortions at the two interfaces. Consequently, another series of films was grown in an attempt to distinguish these sites. These films were essentially identical to the 9 ML film above, but the Fe layers were composed of 56Fe, with a 2 ML 57Fe probe layer effused at the bulk and at each interface in turn. At this point 57Fe MÖssbauer spectroscopy was used to determine the hyperfine field and its temperature dependence for each of the three sites.

Two series of Fe/Ag multilayers were grown in a Perkin-Elmer 430B MBE system, one of the Fe(110)/Ag(lll) orientation and another of the Fe(100)/Ag(100) orientation. Vastly different techniques were developed by this group and others to achieve epitaxial growth of both of these systems. Using RHEED, it was inferred that the optimal growth of Fe(110) on Ag(lll) occurred at a substrate temperature of 180° C. In contrast, the growth of Fe(lO0)/Ag(100) proceeded with the sharpest RHEED streaks at a reduced substrate temperature. We believe that these fundamentally different growth parameters are the result of physically different growth modes, conjectured to be: edge growth (Fe 110), and a more nucleated growth (Fe 100).

Accordingly, dissimilar magnetic interfacial properties are also strongly in evidence, accounted for by the structural differences associated with the different Fe planes. Furthermore, Fe(110) layers as thin as 3 ML were grown on Ag(lll) and showed no superparamagnetism and a genuine 2-dimensional behavior of M(T). However, the Fe(100) on Ag(100) multilayers in a similar thickness range exhibited strong relaxation and a comparatively reduced Curie temperature.

Fe/Mo multilayers, with varied Fe single layer thickness, tF, and Mo single layer thickness, tMO, were deposited by using a focusing ion-beam sputtering technique. Their structural and magnetic properties were studied. The periodic modulated structure was observed for all samples. An enhancement of magnetization over the value of bulk Fe was noticed for some samples. The change of lattice spacing of Fe layers, as a result of compress stress in the film plane, was considered to be responsible for the increase of the magnetization for Fe/Mo multilayers.

We have investigated the magnetic order, using SQUID magnetometry, for short modulation wavelength Fe3O4/NiO superlattices, grown on single crystal MgO. Ferrimagnetic Fe3O4 has a saturation moment of ~500 emu/cm3 at 0 K and a Curie temperature of 858 K, while bulk NiO is antiferromagnetic with a NMel temperature of 525 K. Very high crystalline quality with little interdiffusion is indicated by X-ray diffraction, SEM, optical microscopy, and in-situ RHEED, and the samples show highly anisotropic electrical conductivity which also indicates the strong modulation present. Long wavelength samples (Amod > 200 Å) have a behavior only slightly different from that expected from bulk Fe3O4, but for Amod<80 Å, spontaneous magnetization is replaced by paramagnetism, with weak temperature dependence (not I/T) from 5 K to 400 K.

Three kinds of copper oxide (CuO) films, that is, CuO mono-layer films (MLFs), CuO/A12O3 artificial superstructured films (ASFs) and CuO/MgO ASFs were prepared by a reactive vapor deposition method. Magnetic susceptibility of the MLFs is almost constant against temperature and the Neel temperature (TN) is a little lower than that of bulk CuO. There is paramagnetic contribution proportional to the number of the interfaces for both kinds of ASFs. It is considered to be caused by imperfect -Cu-O-Cu- antiferromagnetic superexchange interactions located in the vicinity of interfaces.

We calculate the absorption of infra-red radiation by a magnetic superlattice composed of alternating ferromagnetic films. Although the films are ferromagnetic, the interfacial interaction is antiferromagnetic (i.e. Fe/Gd or Co/Gd). As has been shown previously, such a system can exist in several distinct phases, and we calculate the power absorption for these different phases. The spin wave modes of the system were found and used to construct a Green's function via an eigenvector expansion. The incoming radiation was modeled as an oscillating magnetic field which was assumed to decay into the material. Given this driving field, the Green's function yields the response of the system. Our results indicate that a simple absorption measurement can be used to probe for surface and bulk magnetic phase transitions. Additionally, we can find the response of the system to a spatially uniform driving field and thus calculate the local susceptibility. We discuss the possibility of using such a susceptibility to find dipole-exchange modes in magnetic superlattices.

Multilayer films consists of noble metal (Pd, Pt, Cu, Au, PdSi) and transition metal(Co, Ni, PdCo, PtCo, CoZr) layers were prepared by rf sputtering method on glass and/or MgO single crystal substrates. The perpendicular magnetic anisotropy was examined in relation to the magnetostriction, lattice misfits, crystallinity and crystal orientations. The results suggest that the perpendicular magnetic anisotropy in noble metal/PdCo alloy multilayers originates from the magnetoelastic energy of the PdCo layers under a stress due to the lattice misfits. In both Pd/Co and Pd/Ni multilayers, the anisotropy was found to depend on the crystal orientation, and the dependence is discussed from the view point of the magnetoelastic surface anisotropy.

We have extended the Neél model of surface anisotropy in b.c.c. crystals to include next nearest neighbor interaction. Fitting the experimental data for Fe (001) and (110) surfaces leads to some pradoxes which cast doubt on the Neél surface anisotropy as the dominant source of surface anisotropy in thin films.

We consider the anisotropies due to coherency strains and the inilioliogcliotis stratlus associated with misfit dislocations, both of which give rise to anisotropy through maguctostrictive coupling. Coherency strains can give rise to anl apparent surface anisotrnpy due to the decrease in coherency strain with the film thickness. This anisotropy is comparable in magnitude to that observed experimentally for Fe [110] epitaxial thiut films on W [110]. The strain field associated with misfit dislocations produces a. surface anisotropy which is also comparable in magnitude to experimentally observed anisotropies. Dislocatioms along the inplane [001] and [110] directions both produce the same preferred direction of maguctization orientation.