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A study was conducted to analyze structures supporting enhanced magnetic properties for giant magnetoresistance applications. Atomic force microscopy was utilized to monitor roughness and grain size. Experimental results indicated that grain size increased with thickness and correlated with poor switching for cobalt rich alloys. thin iron, chromium and tantalum interlayers were effective in suppressing grain growth and maintaining (111) texture.

A study was conducted to analyze the ferromagnetic resonance spectra of thin alloy films. The films were deposited by magnetron sputtering. Experimental results indicated that linewidths and coercivity increased as a function of the total (Cu+magnet) layer thickness at about 20 nm. Findings also showed that the linewidth was sensitive to the damping parameter for the thinner films and to magnetocrystalline anisotropy.

With the microelectromechanical system (MEMS) flux concentrator, we have been able to increase the operating frequency of small magnetic sensors above the region where 1/f noise dominates. The device accomplished this by modulating the field via the oscillatory motion of flux concentrators on MEMS flaps. Electrostatic comb drives were used to drive the MEMS flaps. We have demonstrated an increase in the signal to noise ratio at 1 Hz, that the power signal correctly depends on V4 where V is the amplitude of the voltage energizing the comb drives, and that the signal increases dramatically with vacuum packaging. [ABSTRACT FROM AUTHOR]

To take advantage of the potential offered by the recent increase in the magnetoresistance of magnetic tunnel junctions, it is necessary to address the problem of 1/f noise. ARL has been working on a device, the microelectromechanical system (MEMS) flux concentrator, that mitigates this problem by modulating the sensed magnetic field so that the sensor operates at a higher frequency region where the 1/f noise is smaller. Initial results of testing the device are reported. Though the final step in the fabrication of the device appears to have adversely affected the MEMS motion, two important results were obtained. They are (1) applying the large amplitude voltage at kilohertz frequencies necessary to drive the MEMS structure does not increase the background noise and (2) even though the width of the drive voltage is several hertz, one can demodulate the signal using a lock-in amplifier in order to extract 1 Hz modulation signals. This last result shows that the sensor can be used to detect slow moving or varying magnetic anomalies. [ABSTRACT FROM AUTHOR]

The ferromagnetic resonance properties of thin polycrystalline layers in the sequence Cu/Fe/Cu/Fe/Cu, grown on Si wafers, were studied. Fe grown on Cu can have a very narrow ferromagnetic resonance (FMR) linewidth. Similar structures are of interest for spin transport studies and for giant magnetoresonance applications. The thinner Fe underlayer ranged from 2 to 5 nm, the intermediate Cu spacer thickness from 2 to 10 nm, and the Fe outer layer was 20 nm thick. The increased damping of the thinner Fe layer in this structure, as reflected in the FMR linewidths observed at 9.46 and 33.5 GHz, is similar to that predicted by Berger and recently observed experimentally using epitaxial single crystal Fe films. In addition to confirming the 1/(Fe layer thickness) dependence of the additional damping, the present measurements show a decrease of damping with increasing Cu spacer thickness, implying a short spin transport decay length in our Cu of about 3.5 nm. The linewidth in isolated Cu/Fe/Cu layers also increased with decreasing Fe thickness, as predicted and observed in some other cases. Magnetization data indicate negligible magnetic coupling of the Fe layers except for the smallest interlayer Cu thicknesses used. The linewidths studied increased moderately with cooling to 77 K. [ABSTRACT FROM AUTHOR]

The effects of grain/particle size and morphology on the coercivity of Sm[SUB2](Co[SUB1-x]Fe[SUBx])[SUB17] based powders and spin cast ribbons are investigated in an attempt to make pure Sm-Co 2:17 magnets with a higher energy product than that currently available. It is observed that the coercive force is not only affected by the composition, but also significantly by the grain/particle size. The coercivity of the as-cast SmCo[SUB6] powder was increased from 0.5 to ∼12 kOe when the grain/particle size was decreased from 14 to 1.5 μm. A twofold increase in coercivity was also observed for some Sm(CO[SUB0.85]Fe[SUB0.15])[SUB7.6] spin cast ribbons when the wheel speed was increased from 6 to 25 m/s and the grain size of the ribbons was decreased from 2-15 to 0.5-5 μm. The initial magnetization curves show a high degree of texture that exists in the free side of ribbons, with the c axis parallel to the longitudinal direction of the ribbons. The presence of a trace of boron in the ribbons changes the grain morphology and eliminates the texture. Some results show promise of making a high coercivity higher energy product Sm[SUB2](Co[SUB1-x]Fe[SUBx])[SUB17] based magnets without adding nonmagnetic elements such as Cu and Zr. [ABSTRACT FROM AUTHOR]