G. P. Felcher

Non-oscillatory antiferromagnetic coupling in sputtered Fe/Si superlattices

A series of sputtered Fe(30{Angstrom})/Si(x) superlattices were grown for x=10--40{Angstrom}. Magnetization and Kerr hysteresis loops, and neutron-reflectively measurements identify antiferromagnetic (AF) coupling of the Fe layers at room temperature for x=15{Angstrom} nominal thickness, with switching fields of 6kOe. X-ray structural analysis indicate that the spacer medium is crystalline for x<20{Angstrom}, while sputtered Si is amorphous (a). Failure to detect oscillations in the AF coupling for thicker Si layers is due to the formation of a-Si, as opposed to the crystalline silicide responsible for the coupling.

Antiferromagnetic interlayer exchange coupling in sputtered Fe/Cr multilayers: Dependence on number of Fe layers

The antiferromagnetic arrangement of the magnetic moments of Fe layers in sputtered Fe/Cr multilayered structures is directly demonstrated from polarized neutron reflectometry studies. Such an antiferromagnetic interlayer exchange coupling is also consistent with magnetization studies on a series of [Fe/Cr]N structures. A remanent magnetization is observed for structures containing an odd number of bilayers but no remanent moment is found for an even number of bilayers. By examining the dependence of saturation field on the number of bilayers it is shown that the antiferromagnetic coupling strength is independent of the number of bilayers and is the same for superlattice and sandwich structures.

Training effects and the microscopic magnetic structure of exchange biased Co/CoO bilayers

Exchange bias of a partially oxidized thin film of ferromagnetic Co was studied by magnetization measurements and polarized neutron reflectivity (PNR). The magnetization curve shows strong effects of training with cycling of the magnetic field. Reflectivity measurements with the field parallel to the cooling field showed the onset of spin-dependent diffuse scattering—off the specular reflection—after a training cycle. Such scattering, of the Yoneda type, is due to misaligned Co domains possibly close to the Co/CoO interface. Subjecting the field cooled Co/CoO pair to a field perpendicular to the cooling field causes a rotation of the magnetization. The PNR measurements confirmed earlier susceptibility studies by indicating that the rotation of the magnetization is reversible in fields up to 400 Oe. The rotation of the magnetization of Co is uniform across the film thickness.

Magnetic decoupling in sputtered Fe/Si superlattices and multilayers

Sputtered Fe/Si superlattices were grown to study the magnetic coupling between ferromagnetic Fe layers (30 A thick) for Si spacer‐layer thicknesses (tSi) between 10 and 40 A. The material is ferromagnetical for tSi≤13 A and antiferromagnetically coupled for 13 A≤tSi≤17 A. For tSi≥17 A the Fe layers are uncoupled. X‐ray analysis indicates that the system is well layered, but that the crystal structure remains coherent only for tSi≤17 A. These results, along with our Mossbauer investigation, strongly suggest that the Si layer is crystalline for tSi≤17 A, and is silicide in nature. For thicker spacers, Si becomes amorphous. We propose a model of the layering that is consistent with the known properties of Fe silicide.

Observation of magnetic dead layers at the surface of iron oxide films

Depth profiles of the magnetization of sputtered films of Fe3O4 and its oxidized form, γ‐Fe2O3, were obtained by the new polarized neutron reflection technique. We find that the magnetization of Fe3O4 is constant throughout the thickness (2600 A) of the film except for a surface region about 25 A deep corresponding to the surface roughness. In contrast the oxidized sample shows a magnetically dead layer ∼150 A thick at the surface. X‐ray and transmission electron microscopy studies give no evidence that the surface layers differ structurally from the bulk of the film, although there is the possibility of a highly defective surface region formed during the oxidation process.

Ferromagnetic domain distribution in thin films during magnetization reversal

It is shown that polarized neutron reflectometry can determine in a model-free way not only the mean magnetization of a ferromagnetic thin film at any point of a hysteresis cycle, but also the mean-square dispersion of the magnetization vectors of its lateral domains. This technique is applied to elucidate the mechanism of magnetization reversal of an exchange-biased Co/CoO bilayer. The reversal process above the blocking temperature

Combining of neutron spin echo and reflectivity: a new technique for probing surface and interface order

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Magnetic Structure of MnAs and MnAs0·92P0·08

is governed by uniaxial domain switching, while below

Antiferromagnetic and ferromagnetic order in Co/Ru multilayers

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Neutron diffraction analysis of a compositionally modulated alloy of nickel-copper☆

the reversal of magnetization for the trained sample takes place with substantial domain rotation.