(NiFe/Cu/Co/Cu) Multilayers grown on (100) Si by RF sputtering have been studied by transmission electron Microscopy. The samples are found to be polycristalline and are only weakly textured. The period of the multilayers is clearly visible by small angle electron diffraction and Fresnel imaging. The waviness of the layers appears to be related to the columnar structure of the samples. Experimental images with Fresnel contrast are compared with simulations in order to assess the thickness and roughness of each individual layer.

Elastic neutron scattering measurements performed at the NIST reactor have been used to measure the staggered magnetization near the transition temperature in a thin antiferromagnetic epitaxial film of FeF2 of thickness 0.8μm and diameter 1cm grown on a diamagnetic (001) ZnF2substrate by MBE. The use of a thin film permits extinction-free Bragg intensities, something which has proven impossible in bulk crystals. The growth techniques yield sufficient crystal quality to observed resolution limited Magnetic Bragg scattering peaks and to approach the transition within a reduced temperature of |t| = 0.003. The structure quality of this sample has been characterized using X-ray double crystal diffraction with a measured rocking curve lin ewidth of less than 30 arc sec. The sample thickness, while small enough to eliminate extinction, is sufficiently large to assure three-dimensional Ising Model critical behavior. We indeed observe critical behavior consistent with theoretical predictions. The success of the thin film experiments demonstrates the possibilities of extinction-free Bragg scattering measurements in a variety of antiferromagnetic Materials, including multilayered systems.

We have used polarized neutron reflectivity to study the magnetic microstructure of two Fe/Cr (100) superlattices grown by molecular beam epitaxy. The first film, of nominal composition [0.9 nm Cr/5.5 nm Fe]5, and atomically sharp interfaces, exhibits classical collinear antiferromagnetic structure. The other film ([1.2 nm Cr/5.5 nm Fe]5), grown at a higher temperature, shows the field-dependent non-collinear features attributed to biquadratic coupling. We will describe these measurements and our preliminary structural analysis.

Indirect Magnetic coupling in sputtered Ni/Ag Multilayers has been recently studied by magnetization and magnetoresistance techniques. These experiments indicate that coupling is anti ferromagnetic through 11 and 30 A of silver, and probably ferromagnetic through 20 Å. We present here direct evidence for such a magnetic coupling for all three thicknesses, as obtained from low angle neutron scattering experiments. Multilayers in which the Ag layer thickness is either 11 or 30 Å both exhibit a supplementary diffraction peak at a q value corresponding to twice the chemical period. Its evolution with both temperature and applied field confirms its purely magnetic origin. In order to study the coupling through 20 Å of silver, we prepared a multilayer in which the Ag layers are alternately 11 and 20 Å thick. In this case, we also observe a doubling of the chemical period. The coupling through 11 Å being anti ferromagnetic, this unambiguously shows that the coupling through 20 Å is ferromagnetic.

Antiferromagnetically coupled (Co17A°Re5A°)×15 superlattices were deposited simultaneously onto glass and Si substrates, with an intervening Re buffer layer. Samples grown on glass show sharper interfaces than those grown on Si. This effect reflects on Magnetoresistance, Magnetization, Rutherford backscattering, and hyperfine field results. The influence of the Re buffer layer thickness and annealing temperature on these properties is discussed.

The role of interfacial exchange coupling in the magnetic behavior of metal oxide materials has been investigated through the study of Fe3O4/NiO superlattices. We report results on a series of superlattices grown where one bilayer constituent was held to a fixed thickness while varying the other from single unit cell dimensions upward. High crystalline quality was confirmed by XRD, RHEED and neutron diffraction. Magnetization profiles show substantial deviations from bulklike iron oxide results, with an increase in domain rotation energies observed in the superlattices over that of bulk iron oxide (increasing with NiO layer thickness) indicating the strong nature of Fe3O4/NiO interfacial linkage. Neutron scattering at elevated temperatures shows that the NiO remains ordered above the 523 K bulk Néel temperature. This suggests that at least a portion of the NiO within a layer remains ordered well above the Néel temperature, with an increase in effective Néel transition temperature that approaches the Fe3O4 Curie temperature in the limit of very thin NiO layers. Although the exchange coupling dominates these effects, strain also plays an important role.

Single layers of Co82?l8 with thickness in me ranee of 100–1500Å and multilayers of Co-Cr/Al with Co-Cr thickness in the range of 100–200A and Al at 7Å were prepared by dc magnetron sputtering. The films were deposited on to Si (111) and glass substrates at room temperature. A 100Å thick Al buffer layer was deposited to improve the c-axis orientation. X-ray diffraction (XRD) Measurements on the multilayers show a predominant Co-Cr (00.2) peak. Polar Magneto-optic measurements were performed to determine the Kerr rotation (θK) and figure of Merit. The results indicated an enhancement in the figure of merit at λ = 632.8 nm for the multilayered structures compared to single layer samples. All of the films show a 4πMs value around 6 kG and ferromagnetic resonance measurements indicate an enhancement in the perpendicular anisotropy field for the 150Å multilayered sample.

A quantitative determination of interface (Ks) and volume anisotropy {?ψ) constants of MBE and sputtered CO/Pt Multilayers is reported. Torque and VSM Magnetometry were used to determine the total average anisotropy and the room temperature magnetization of four different series of films with varying Co thickness and nearly constant Pt thickness. All films were characterized with X-ray diffraction and X-ray fluorescence, allowing the determination of the “Magnetic” volume with good accuracy. Both Ks and Jeff are found to be orientation dependent. We find the following results for MBE films grown on Ag buffered GaAs substrates and highly < 111 > textured films, grown on etched SiNx buffers:

(111) Ks = 0.97mJ/m2, Kveff =-0.74MJ/m3 MBE

(111) Ks = 0.92mJ/m2, Kveff =-l.lIMJ/m3 sputtered

(110) Ks = 0.42mJ/m2, Kveff =-l.95MJ/m3 MBE

(001) Ks = 0.59mJ/m2, Kveff =-5.98MJ/m3 MBE

The [110]-oriented MBE films show in addition a large (intrinsic) in-plane anisotropy constant K‖0≃-3MJ/m3 which is found to be independent of the Co thickness. [100] is the easy and [110] the hard in-plane direction.

Structural features in magnetic multilayer films such as interfacial sharpness and in-plane stress are regarded as responsible for the perpendicular magnetic anisotropy observed in these films. The Multilayers often consist of alternating magnetic and non-Magnetic layers, and the degree of interfacial sharpness between the two is a critical component in producing perpendicular anisotropy. Additionally, in-plane stress affects the anisotropy through Magnetostriction. In this work, we measure both the composition modulation and the stress in multilayers of Pt/CO with x-ray diffraction. Quantitative information about the composition modulation is extracted by recursively fitting a model of multilayer diffraction to the high angle superlattice lines. The Model incorporates a composition modulation of variable amplitude, along with a statistical description of the layer thickness fluctuations.

We report on the magnetic and Magneto-optical properties of PtFe and PtCo intermetallic thin films when they have the CuAu(I) tetragonal structure and their crystallographic C axis is oriented out of the film plane. These films possess large perpendicular magnetic anisotropy energies. We observe changes in the Magneto-optic Kerr rotations of Pt-Fe and Pt-Co alloys associated with the formation of the uniaxial CuAu(I) crystal structure. In particular, we report the observation of up to 60% enhancement in the Magneto-optic Ken-rotation for ordered, epitaxial PtFe intermetallic alloy over that of the random face centered cubic alloy. This enhancement is wavelength dependent, with a peak in the visible light range at 2.0 eV.

An experimental study of conventional x-ray absorption and of magnetic circular x-ray dichroism has been performed on Ce/Fe Multilayers at the Ce L2,3 and the Fe-K edge, to characterize the impact of the interaction of Ce and Fe on the local electronic and magnetic structure of the interface. The spectra reveal that the interaction has two effects. First, on a depth scale of up to 15 A near the interface, the Ce atoms adopt the electronic structure of the oc-phase, with itinerant 4f states. Second, a large portion (=10 Å) of these cc-like Ce atoms is magnetically polarized and carries an ordered Magnetic 5d Moment. The Fe-3d and Ce-5d Moments are antiferromagnetically coupled. Interface Mixing on a length scale of the magnetic polarization can be excluded.

We have sputter-deposited a series of Pt/CO Multilayers with differing amounts of rare-earth (RE) in an effort to improve the uniaxial perpendicular anisotropy in these structures. The present work investigates the influence on the magnetic properties of Tb and Ho incorporated both at the interfaces of Pt/CO Multilayers and into the Co layers. The uniaxial anisotropy improved significantly only for those multilayers that showed poor perpendicular anisotropy in the undoped state, in particular, those with large (∼30 Å) bilayer periods. High resolution transmission electron microscopy was used to study these multilayers in cross-section. The Multilayer structures present strong [111] texture with grain sizes ranging from 200 to 600 Å. It is found that the RE does not produce a significant change in the growth texture of the multilayers until a critical amount is introduced beyond which the multilayer structure amorphizes resulting in a compositionally modulated amorphous film.