CoNiCu/Cu superlattice nanowires have been grown by electrodeposition in nuclear tracketched nanoporous membranes. Transmission electron microscopy (TEM) images show a good layer structure and allow an estimate of the current efficiency. Current perpendicular to plane (CPP) giant magnetoresistance of up to 22%, at ambient temperature, has been measured but appears to be limited by defects, giving rise to ferromagnetic interlayer coupling, at low nonmagnetic layer thicknesses. Magnetic properties of the superlattice nanowires are influenced by in-plane anisotropy and magnetostatic coupling.

Recent work1 has highlighted the possibility that through the introduction of metals into the one-dimensional channels of zeolite L, it may be feasible to engineer charge transport along the channels to produce a unique compound comprising a precise, assembled array of ultrafine, atomic-scale conducting wires embedded within the aluminosilicate framework. Using electron spin resonance (ESR), and microwave cavity perturbation measurements, we examine the properties of these remarkable materials as a function of composition as they approach the insulator to metal transition.

A magnetic field sensor based on the planar Hall effect has been developed using epitaxial permalloy (Ni80Fe20) ultrathin films (1-10 nm). The magnetic and magnetotransport properties of these films have been studied in detail. For thicknesses above 5 nm, the resistivity of the permalloy film is below 5μΩ-cm, and its magnetoresistance ratio is 2%. By using the transverse resistivity for detection, we have reduced thermal drift effects by five orders of magnitude. We also make use of a weak uniaxial anisotropy induced in the permalloy through exchange coupling with a 6 nm-thick Fe/Pd multilayer, itself grown directly on the MgO substrate. Magnetic sensors based on these films have been used successfully to detect fields below 10 nT at 1Hz. Since the lateral dimensions of the sensing element are small (<30μm), and because of the ferromagnetic coupling with the Fe/Pd structure, it consists of a single magnetic domain. Sensitivities above 100 V/T-A have been obtained, with deviations from linearity of less than 2% over 4 decades.

We have observed micromagnetic structure in real computer hard disks with the typical structure of C/Co alloy/Cr/NiP/Al(substrate) using Lorentz transmission electron microscopy (LTEM). A chemical etching method was introduced to successfully prepare LTEM specimens directly from the computer hard disks with both smooth and mechanically textured substrates. Micromagnetic structural features, e.g., ripples and vortices, were studied in disks in bitswritten, ac-demagnetized, and saturation remanent magnetic states.

Coherent epitaxial Fe3O4 layers in the range of 0 to 400 Å have been grown by molecular beam epitaxy on single crystal MgO(100) substrates. The magnetic properties were studied by local magneto-optical Kerr effect experiments on a wedge shaped Fe3O4 layer, by ferromagnetic resonance and SQUID. The results show that the magnetic behavior of the Fe3O4 thin films resembles bulk Fe3O4 in the investigated thickness range.

We report on the phase transformation of amorphous PtMnSb thin films induced by laser annealing in the nanosecond time regime. Structural and magnetic transformations are investigated by TEM, XRD, AFM and in-situ MOKE and VSM. We have established that a minimum laser fluence is required to crystallize the amorphous films and thus, to induce magnetic activity. The transformation kinetics vs number of irradiation pulses reveals that the magnetically active C1b phase is formed via an intermediate phase, namely, tetragonal-PtMn. We have also established that the thin film crystallization induced by the nanosecond laser annealing proceeds via nucleation rather than grain growth. Measurement of the lattice parameter of the C1b-PtMnSb produced by the laser quenching (LQ) indicates an essentially unstrained structure with a =6.17 Å vs a =6.201 Å reported for the bulk. Nevertheless, we observe the generation of large surface undulations upon laser annealing and suggest that this is the mechanism for stress relaxation concomitant with the large volumetric changes involved in the phase transformation. In addition, we observe decrements in saturation moments and Curie temperatures which are attributed to the nanocrystalline nature of the LQ specimens.

Novel material structures that combine magneto-optic (MO) and semiconductor devices have potential applications in monolithic microwave systems and optoelectronics. We have investigated the materials issues pertaining to the film structure, interface uniformity, and magnetic/MO properties of (BiDy)3(FeGa)5O12 (Bi-DyIG) thin films sputter deposited on Si and GaAs. The rapid thermally annealed films were polycrystalline with a nominal grain size of 20 nm. The magnetic and MO properties were strongly dependent on the type of substrate such that square hysteresis loops and coercivities of 0.1 to 0.9 kOe were observed for Bi-DyIG/Si structures while Bi-DyIG/GaAs structures showed much lower coercivity values (0.03 kOe). A comparison of the magnetic properties, microstructure and substrate composition was carried out with plan-view and cross-section transmission electron microscopy, as well as electron and x-ray diffraction. The results suggest that grain orientation effects, stress, and compositional inhomogeneity due to interfacial reactions or diffusion introduced by the substrate strongly influence the magnetic and MO properties of the films.

In the past years artificially-structured materials have been grown with an increasing degree of sophistication due to steady progress in our ability to control growth processes down to the atomic level. These materials have yielded new physical properties due to the confinement of electrons in less than three dimensions. Thus, the confinement of electrons in two-dimensional (2D) metallic superlattices has resulted in oscillatory magnetic coupling with an associated oscillatory giant magnetoresistance (GMR). New properties are expected when the electrons are further confined to one dimension (1D) of free motion in the structures known as quantum wires. In this report we briefly describe two recent examples of atomic-scale engineering of materials. In the first case a surfactant is used to purposely modify the structure of magnetic/non magnetic superlattices. The second example illustrates a further reduction in dimensionality obtained by modifying the substrate onto which the growth takes place: the fabrication of 1D magnetic quantum wires on vicinal surfaces.

Owing to the sensitivity of the hyperfine field to the topological and chemical environment of the probe nuclei, NMR spectra can be considered as histograms of the short range order ruling the structure of the material under investigation. Complementary to diffraction techniques this gives a local insight on the structure in the direct space. We review recent structural investigations of cobalt layers imbedded in Co/X multilayers and particularly of buried interfaces. Special attention has been given to the way intermixing takes place at the interfaces as its influence on the multilayer properties may be of considerable importance. Co/Cu multilayers, a case of weakly miscible elements, have been specially investigated owing to their GMR properties. But also cases of solid solution forming elements (Co/Ru or Co/Cr) or compound forming elements (Co/Fe) have been thoroughly studied. The latter case, which shows a stabilization of a bcc Co phase, will be discussed against the bulk alloy phase diagram.

The growth of Fe/ZnSe/Fe multilayers on (001) and (111) GaAs substrates is reported. The samples were characterized in-situ by reflection high energy electron diffraction (RHEED), and ex situ by vibrating sample magnetometry (VSM), ferromagnetic resonance (FMR), cross sectional transmission electron microscopy (TEM), and x-ray diffraction. On the (001) surface, the quality of the layers deteriorated significantly with the growth of the first ZnSe spacer layer. In Fe/ZnSe/Fe trilayer structures, TEM revealed a well-defined layered structure, with a high density of defects in both the ZnSe spacer layer and the subsequent Fe layer. VSM and FMR clearly showed the presence of two Fe films with distinct coercive fields, with the higher coercive field attributed to the lower crystalline quality of the second Fe layer. θ-2θ xray diffraction measurements performed on samples grown on (001) GaAs substrates indicated that the ZnSe spacer layer (grown on (001) Fe) grew in a (111) orientation. Growth on GaAs(111) substrates produced better RHEED patterns for all layers with little deterioration in film quality with continued layer growth, so that the magnetic properties of the individual Fe layer could not be distinguished.

The effect of in-plane strain in (111)-oriented epitaxial TbFe2 films on the magnetization orientations was studied. Magnetocrystalline anisotropy, shape anisotropy, and magnetoelastic energy were calculated to determine the magnetization orientation in the presence of various in-plane strains. Theoretical considerations indicate that a compressive strain smaller than -0.065% can induce an out-of-plane magnetization. DC magnetron sputtering from Tb and Fe elemental targets was used to grow 50, 100, 200, and 400 Å thick epitaxial TbFe2(111) films at 600°C on (110)-oriented sapphire substrates with 1000 Å thick epitaxial Mo(110) buffer layers. The growth rate of the TbFe2(111) films was 1.44 Å/sec. X-ray diffractometry, Rutherford backscattering spectrometry, and vibrating sample magnetometry were used to characterize the crystal structure, epitaxial orientation, composition, stress and strain state, and magnetic properties of the TbFe2 films. The TbFe2(111) films were epitaxial with twins rotated by 60° and were in tensile strain states with the resulting in-plane magnetization.

τ MnAl / Co superlattices are grown epitaxially on GaAs (100) substrates by molecular beam epitaxy. High angle XRD spectra are analysed and indicate that good structural quality is achieved. The behaviour of the superlattice upon annealing is described and compared with inplane and out of plane magnetization data. Extraordinary hall effect measurements show low field switching comparable to MnAl thin films. Arguments on how structural properties are affecting the magnetic properties are discussed.

FePt alloy films were deposited at 50 and 49°C onto amorphous SiO2 and single crystal [001] MgO and [0001] Al2O3 using DC magnetron cosputtering, resulting in polycrystalline and [001] and [111] epitaxial films, respectively. High temperature deposition resulted in ordered films with the tetragonal Ll structure and out-of-plane magnetic easy axes while low temperature deposition yielded chemically disordered fcc alloys with in-plane easy axes. Significant modification of the magneto-optic Kerr spectrum is observed for ordered relative to disordered alloys for all orientations. The Kerr rotation has a strong orientation dependence for the ordered, but not disordered films.

The magnetic and structural properties of Co in Mo/Co multilayers are an unresolved issue. Two independent studies report different structures for thicker Co layers in multilayers of comparable dimensions as well as significant differences in both the form and the layer thickness for a loss of ferromagnetism. Both studies base their structural claims on a limited number of Bragg lines. We have used x-ray diffraction, transmission electron diffraction, and EXAFS to probe the structure of Mo/Co multilayers having Co layer thicknesses from 4 to 63Å. Our structural and magnetic results for these samples are compared to those of the above studies and are contrasted with results for Mo/Fe multilayers having comparable dimensions.

Fe-N thin films have attracted considerable attention because they are potential candidates for magnetic recording with their large saturation magnetization and their good corrosion resistance1. It has even been demonstrated that saturation magnetization can be larger than the bulk iron one for low nitrogen contents2. The origin of the enhanced magnetic moment could occur from the metastable α″ Fe16N2 phase or from an expanded bcc FeN structure which is also called α FeN.

In this paper we report the successful growth of single-phase epitaxial PtMnSb films and multilayers by dc magnetron cosputtering, both in the (001) orientation on MgO(001) and W(001), and in the (111) orientation on Al2O3 (0001). Single-layer films in the thickness range 50Å≤t≤1000Å were grown and characterized using x-ray diffraction (XRD), magneto-optic Kerr effect (MOKE), and vibrating sample magnetometry (VSM). The in-plane orientation relationships, as determined by asymmetric XRD, were PtMnSb[100]∥MgO[110], PtMnSb[100]∥W[100], and PtMnSb[101∥Al2O3[2110]. The crystalline quality of the films was found to depend strongly upon the substrate, growth temperature, film thickness, and presence of a capping layer, but rocking curve widths of 1° or less were achieved on each substrate. Measurement of the in-plane strain showed that the films were almost entirely relaxed, with strains <1%. In-plane magnetization was observed in all cases, with moments and coercivities in the 400-500 emu/cm3 and 100-200 Oe ranges respectively. Polar Kerr spectra showed large rotations (0.75° - 1.03°), whose peak wavelengths appear to depend on both film structure and optical interference effects.

Sputter deposited MnSb thin films were annealed utilizing KrF excimer laser pulses (16ns), and the resulting structural and magnetic changes investigated. These changes are compared to those observed when the samples are subjected to isothermal and rapid thermal annealing treatments. Isothermal and rapid thermal annealing induce significant lateral grain growth, whereas the laser treatment produces vertical grain size refinement with no appreciable lateral growth. Annealing is shown to increase the hexagonal c-axis, reaching an expansion value of 7% for the laser annealed samples. This c-axis expansion has a strong influence on the magnetic properties of the thin films. Mechanisms for the c-axis expansion are discussed.

The magneto-optical (MO) layer in current rare earth-transition metal (RE-TM) based MO recording media is typically 20 nm to 60 nm thick. It has been suggested, however, that media structures employing a multiplicity of thinner MO layers may be advantageous, e.g., for multilevel recording applications [1] or media noise reduction [2]. As magnetic layer thickness is reduced, interactions among magnetic layers and adjacent materials can have an increasingly large influence on magnetic properties; in many instances, these interactions can dominate the observed magnetic behavior.

As a means of studying MO layer - adjacent layer interactions, we have used thin (≈3 nm) films of several materials to separate single 24 nm thick ion-beam-deposited FeTbCo layers into N thinner layers of 24/N nm thickness (N × 24/N). As N increases, the FeThCo magnetic properties generally change; however, the relative magnitude of the changes is strongly dependent upon the adjacent layer composition. Magnetization (Ms), energy product (MsHc) at 30 C and Curie temperature data for 1 × 24 nm structures and 6 × 4 nm structures are compared and discussed for specimens employing SiCx, Six, YOx, HfOx, Si and SiOx adjacent layer materials.

Brillouin light scattering (BLS) and magneto-optic Kerr effect have been carried out on a series of specimens consisting of a Fe(001) whisker substrate upon which thin Cr(001) and Fe(001) layers have been deposited by means of molecular beam epitaxy in ultrahigh vacuum. The Fe film was 20 monolayers (ML) thick, and the Cr(001) films were grown having various thicknesses. It is demonstrated that BLS thin film frequencies measured in the saturated magnetic state with the thin film magnetization parallel with the applied magnetic field can be used to obtain the exchange coupling strength between the thin film and whisker magnetizations both for antiferromagnetic coupling and for ferromagnetic coupling, provided that the ferromagnetic coupling is not too strong. It is also shown that the coupling strength is extremely sensitive to the quality of the chromium growth: a small deterioration in the growth conditions has been found to reduce the exchange coupling by nearly a factor of two.

The surface spin-flop and Néel transitions are examined in Fe/Cr superlattices. The surface spin-flop, originally predicted by Mills [Phys. Rev. Lett. 20, 18 (1968)], is observed in Fe/Cr(211) superlattices with antiferromagnetic interlayer coupling and uniaxial in-plane anisotropy. The Néel transition (TN) of Cr is observed in Fe/Cr(001) superlattices, for which the onset of antiferromagnetism is at a thickness tCr of 42Å. The bulk value of TN is approached asymptotically as tCr increases and is characterized by a three-dimensional shift exponent. These TN results are attributed to finite-size effects and spin-frustration near rough Fe-Cr interfaces.