Search

A study of the microstructural and magnetic properties of phase separated Co-rich CoAg very thin films is presented. In the as-deposited state these films form in a very fine grained metastable alloy and are magnetically soft ([H.sub.c]e [less than] 20 Oe) in the thickness (5 - 50 nm) and Co composition range investigated (Co volume percent [greater than] 65 %). After annealing at 420 [degrees] C for 30 minutes phase separation and grain growth occur and the coercivity is now thickness dependent with a maximum around 15 nm. The maximum coercivity as a function of composition is expected to occur around a volume concentration of 50 % for bulk or thick film granular materials. However, for films thinner than 20 nm we have found a maximum He [greater than] 800 Oe at a Co concentration of 70 vol %. This shift in the percolation threshold may originate in the reduced dimensionality of very thin films. Magnetic force microscopy images show a transition in the magnetic domain structure as a function of film thickness that is consistent with this description and the results obtained by transmission electron microscopy. Index Terms - Co-Ag thin films, granular materials, high coercivity, percolation threshold.

The magnetostriction constants, [[Lambda].sub.100] and [[Lambda]y[.sub.111], of FeTaN (10 wt% Ta) were determined in (110) oriented epitaxial thin films ([equivalent] 1500 [Angstrom],) deposited by dc magnetron sputtering onto Cu(001) buffer layers ([approximately]2000 [Angstrom]) which were grown on Si(001) single crystal substrates. The orientation relationship of the films was FeTaN(110)[parallel to]Cu(001)[parallel to]Si (001) with FeTaN[parallel to]Cu [parallel to] Si, which was satisfied by four different, equally probable in-plane orientations of the crystallites. The magnetostriction measurement was carried out on a cantilever beam measurement system calibrated with (110) oriented epitaxial Fe films with the same morphology as the unknown films assuming the bulk values of [[Lambda].sub.100] and [[Lambda].sub.111]. The magnetostriction of FeTaN films was measured as a function of angle in the sample plane and fitted with the calculated average of the four orientations. In conflict with theoretical predictions, it was found that [[Lambda].sub.100] decreases and [[Lambda].sub.111] increases as a function of lattice dilation which was taken to be proportional to the interstitial concentration. At larger normalized lattice dilation, [approximately]2%, [[Lambda].sub.111] changed sign from negative to positive. The calculated saturation magnetostriction, [[Lambda].sub.s], using these values of [[Lambda].sub.100] and [[Lambda].sub.111], agreed with published data on nanocrystalline samples of the same composition with no additional assumptions. Index Terms - FeTaN, magnetostriction, nanocrystalline alloys.

The temperature dependence of the coercivity of ultrathin NiFe films was measured by SQUID in the temperature range from 5 to 300 K. The change in coercivity with temperature was much greater for thinner films than for thicker ones. A domain wall motion model is proposed to explain the experimental results. It is concluded that the intrinsic coercivity increases rapidly with decreasing the thickness, especially in the range of several nm, and that the low coercivity observed for very thin films at room temperature is ascribed primarily to the thermal effect.

The microstructure of [Co.sub.90][Fe.sub.10]/Ag GMR multilayer films has been investigated using x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Columnar grain growth with a (111) fiber texture is observed. A direct correlation is made between superlattice satellite peak signals from selected area electron diffraction (SAD) and XRD.

Initial permeability and transverse bias permeability measurements have been made on [NiFeCo(t)/Cu(23[Angstrom])]6 multilayers for different magnetic layer thicknesses(t) in the as-deposited state and after an annealing treatment. The initial permeability was found to be independent of frequency up to at least 100 MHz and to increase with magnetic layer thickness. The transverse bias permeability is used to calculate the effective uniaxial anisotropy and the bilinear and biquadratic exchange fields. The thicker multilayers are found to be ferromagnetically coupled in the as-deposited state and upon annealing a transition occurs producing antiferromagnetically coupled magnetic layers.