T.J. Klemmer

High coercivity nanostructured networks

Films of Fe, Co, and Co35Fe65 alloy have been sputter deposited onto the surface of porous nanochannel alumina substrates producing nanostructured contiguous magnetic “networks.” Large room temperature coercivities have been measured which approximately scale with the bulk saturation magnetization of the material used. In the as-deposited state the largest coercivities (e.g., >1000 Oe for Co35Fe65) are observed in ∼15-nm-thick networks deposited on the smallest commercially available pore size substrates (those having an average pore diameter of ∼20 nm and a wall thickness of ∼15 nm). Preliminary studies of the effects of annealing indicate that coercivities can be substantially increased (by as much as ∼50%) with an appropriate post-deposition thermal treatment.

Shift in the magnetic percolation threshold of phase separated Co-rich CoAg very thin films due to reduced dimensionality

An investigation of the structural and magnetic properties of phase separated Co-rich CoAg very thin films (5 nm–50 nm) as a function of film thickness and Co concentration is presented. In the as-deposited state the films are very fine grained and the coercive field is relatively low (Hc<20 Oe). However, after annealing at 420 °C for half an hour in high vacuum, grain growth is promoted and a drastic change in the magnetic properties is observed. The coercivity now has a strong thickness dependence with a maximum at approximately 15 nm. The largest room temperature value of coercivity, Hc=850 Oe, was found for a CoAg 70:30 volume percent alloy. The concentration of maximum coercivity is usually associated with the percolation threshold, xp, of the ferromagnetic element and is much higher than the ∼50 vol % value normally observed in thick film and bulk granular ferromagnets. Values of xp≲0.65 were found for 30 nm thick films increasing up to xp∼0.75 for 10 nm films. This behavior is explained as a shift ...

Exchange induced unidirectional anisotropy observed using Cr–Al antiferromagnetic films

Exchange induced unidirectional anisotropy has been observed in a new bilayer system consisting of a ferromagnetic FeTaN or Ni80Fe20 film coupled to an antiferromagnetic Cr–Al alloy film. Estimates of the exchange coupling energy and magnetic anisotropy constant of the antiferromagnet are made and compared to other exchange coupled systems.

The Effect Of Annealing On

We have previously discussed the preparation of heteroepitaxial (100) (Fe,,Ta,)N films, the measurement of the crystalline anisotropy constant K,, and the magnetostriction constant h,,, and h,, [ l ] 3 T e results showed that K, decreased by a factor of -2 up to 6%N and that the values of 1 hlMYkd 7 h,,, I relative to pure Fe decreased by a factor of -2 to a minimum of near 2 at % nitrogen and then slowly increased at higher nitrogen content. The saturation magnetostriction hs calculated for a polycrystalline material using the values of h,, and h,,, was negative and relatively independent of nitrogen content. This is in sharp contrast with the published experimental data which shows h, increasing from negative values to large positive values with increasing nitrogen [3]. We believe an explanation for this discrepancy is required to properly understand the soft properties of the FeXN systems. Therefore, we have initiated an extensive structural investigation using both x-ray and TEM analysis and an effort to grow (1 10) oriented films, the preferred orientation in polycrystalline films of this composition. Here, we report on our results to determine the location of the nitrogen in the lattice and further its thermal stability.

Magnetostriction constants of [110] oriented epitaxially grown FeTaN thin films

The magnetostriction constants, /spl lambda//sub 100/ and /spl lambda//sub 111/, of FeTaN (10 wt% Ta) were determined in [110] oriented epitaxial thin films (/spl sim/1500 W) deposited by dc magnetron sputtering onto Cu[001] buffer layers (/spl sim/2000 /spl Aring/) which were grown on Si[001] single crystal substrates. The orientation relationship of the films was FeTaN[110]/spl par/Cu[001]/spl par/Si[001] with FeTaN /spl par/Cu /spl par/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 /spl lambda//sub 100/, and /spl 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 /spl lambda//sub 100/ decreases and /spl 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, /spl sim/2%, /spl lambda//sub 111/ changed sign from negative to positive. The calculated saturation magnetostriction, /spl lambda//sub s/, using these values of /spl lambda//sub 100/, and /spl lambda//sub 111/ agreed with published data on nanocrystalline samples of the same composition with no additional assumptions.

Electrical resistivity in sputtered Co90Fe10/Ag GMR multilayers

An analysis of room temperature electrical transport properties in sputtered (Co90Fe10/Ag) giant magnetoresistive multilayers is presented. The Co90Fe10 and Ag thickness ranges are both well below bulk electron mean free paths. Layer thickness dependent resistivity is observed and compared to resistivity measurements of single layer Co90Fe10 and Ag films.

Thermal Effect On The Coercivity Of Ultrathin NiFe Films

The temperature dependence of the coercivity of ultrathin NiFe films was measured by a 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 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.

High coercivity in heterogeneous Co-rich CoAg very thin films

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/ 65%). After annealing at 420/spl deg/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 H/sub c/>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.

Microstructure In Sputtered Co/sub 90/Fe/sub 10/ Ag GMR Multilayers

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.

The effect of annealing on [001] FeTaN heteroepitaxial films

The position of the nitrogen in [001] oriented FeTaN epitaxial thin films prepared on [001] MgO by reactive sputtering in an Ar-N atmosphere was determined by X-ray diffraction and its mobility investigated by annealing experiments. Lattice spacing measurements of the [002], (011), (211) and (112) crystallographic planes revealed that the bcc FeTa lattice with the inclusion of nitrogen underwent a tetragonal deformation with the c-axis out of the sample plane and with a maximum tetragonality in these samples of /spl sim/1.02. Upon annealing for two hours between 250/spl deg/C and 650/spl deg/C, the [002] lattice spacing and the crystalline anisotropy changed back to the values measured in nitrogen free films. No change in the magnetization was observed with annealing. The fact that the nitrogen occupies the interstitial sites in the z-direction perpendicular to the film plane may explain the relative insensitivity of magnetic properties measured in the [001] plane to the nitrogen concentration.