W. D. Doyle

Influence of underlayers on the soft properties of high magnetization FeCo films

A remarkable reduction in coercivity Hc was found in sputtered Fe65Co35(=FeCo) films on Cu, NiFe, Ru, Ta/Cu, Ta/NiFe, or Cu/IrMn underlayers. A decrease in Hc from 120 to 7–12 Oe was observed for Cu, NiFe, and Ru underlayers as thin as 2.5 nm but less for Ta. A Cu underlayer significantly reduced the maximum anisotropy fields from 2 kOe to 40 Oe, resulting in a well-defined in-plane average uniaxial anisotropy field Hk∼30 Oe. The saturation magnetostriction with Cu was (47±4)×10−6, independent of Cu and FeCo thicknesses. In-plane tensile film stress decreased with underlayer thickness tUL from 2 to 0.2 GPa but much less rapidly than the reduction in Hc. All underlayers induced a (110) texture in FeCo, which was strongest with Ta. Transmission electron microscopy of cross-sections showed an unusually long range coherence with low angle grain boundaries in the FeCo without an underlayer. Clear columnar grains were visible with all underlayers with an average grain size of ∼50 nm with Ta dropping to 9–10 nm ...

Quantitative correlation of phase structure with the magnetic moment in rf sputtered Fe-N films

Single‐layer Fe‐N films were deposited onto DC biased glass substrates at room temperature by reactive rf magnetron sputtering in an N2‐Ar atmosphere. The Ar pressure was fixed at 6 mTorr and the properties were investigated as a function of N2 flow rate (R). X‐ray diffraction and transmission electron diffraction were used to identify phases in the films. At R=0, the saturation magnetic moment density σS measured in a vibrating‐sample magnetometer (VSM) was 210 emu/g, within experimental error equal to the value for bulk α‐Fe, and only a single phase with the bulk lattice constant of α‐Fe was detected. At R=5 sccm, σS=227 emu/g, and an α‐Fe(N) phase with a ∼1% expanded lattice constant was detected. At R=15 sccm, σS reached a maximum of 247 emu/g and x‐ray and transmission electron diffraction gave clear evidence of the Fe16N2 phase in addition to α‐Fe(N). At R=30 sccm, σS dropped to 196 emu/g, and the diffraction data showed α‐Fe, α‐Fe(N), and a significant fraction of Fe4N. The value of σS calculated f...

Influence of particle size on the magnetic viscosity and activation volume of /spl alpha/-Fe nanowires in alumite films

Particle size effects on the magnetic viscosity and activation volume were studied at room temperature for elongated /spl alpha/-Fe particles in alumite (Fe nanowires in an anodized aluminum oxide film). Both magnetic viscosity and activation volume are strongly dependent on the particle diameter, but independent of the particle length. The magnetization reversal mechanism of elongated /spl alpha/-Fe particles in alumite films is discussed. The activation volume may represent the size of the magnetic switching unit propagating along the particle length during the non-uniform magnetization reversal.

High-speed switching in magnetic recording media

Recent measurements of the high-speed switching behavior of a wide range of commercial and experimental magnetic tapes are summarized. The salient result is the variation with material in the increase in the remanence coercivity HCR(τ) as the field pulse width τ decreases to <1 ns. For high-viscosity materials, the results are in good agreement with the thermal switching model proposed by Sharrock when 1/τ≤f0, the attempt frequency. For low-viscosity samples, the results are in reasonable agreement with the Landau-Lifshitz damping-limited switching model but only if values of the damping constant α ≈ 1 are assumed, in conflict with the experimentally reported values in some samples. The fundamental relationship between the two models through the fluctuation-dissipation theorem is emphasized and the need for a comprehensive model identified. Finally, a strong empirical correlation is obtained between α and a figure of merit SW/HC, where SW is the switching constant and HC is the coercivity. The implications for future media where thermal effects will become more important are significant.

A THEORETICAL DESCRIPTION OF MAGNETIC SWITCHING EXPERIMENTS IN PICOSECOND FIELD PULSES

Siegmann et al. have reported that the magnetization in a perpendicularly oriented CoPt film with a uniaxial anisotropy field of 20 000 Oe was reversed when the film was exposed to a 20 000 Oe in‐plane pulsed field lasting only 6 ps. From a calculation based on the Gilbert form of the Landau–Lifshitz equation (LLG), it is shown that the experimental result is consistent with the LLG model even for values of the damping constant α as larger as 0.5. The dependence of the switching time on the anisotropy field and the applied field are presented as a function of α and the angle β between the applied field and the easy axis. Experiments are suggested which could illuminate the damping mechanism at these very short times.

Synthesis of high moment and high coercivity iron nitride particles

Fe2N particles were prepared by nitriding acicular γ‐Fe2O3 particles (precoated with sodium silicate to prevent the particles from sintering) at about 450 °C for 3–6 h under a mixed stream of H2‐NH3 (1:4 molar ratio). X‐ray diffraction showed mostly Fe4N and small amounts of α‐Fe and Fe2O3, but no Fe8N(α‘‐Fe16N2). The saturation magnetic moment density σS increased to 140–160 emu/g and the coercivity Hc increased to about 1000 Oe. Although the ultimate goal of preparing Fe8N particles was not attained, an impressive combination of magnetization and coercivity was achieved. To obtain Fe8N by chemical doping, the nitrogen content of Fe4N was decreased by coating with metal hydroxides of Ti, Nd, and Sm, and reducing under H2 at 300 °C: the magnetization dropped precipitously, and no Fe8N was formed.

High speed switching measurements in thin film disk media

Thermal switching has been recognized as a possible limit to archival storage in advanced high density recording media. Thinner films with more isolated grains suffer from large magnetic viscosities /spl sim/10%/decade. Previous work has shown that the observed remanent coercivity H/sub CR/(/spl tau/) in high viscosity tapes can be predicted from Sharrocks Law down to 10/sup -9/s. Here we report high speed switching results on thin film media which show that the remanent coercivity at 10/sup -8/s is increased /spl sim/40% relative to the VSM value in these films. A quantitative relationship between the viscosity, irreversible susceptibility, and the increase in H/sub CR/(/spl tau/) is demonstrated.

Epitaxial growth of Cu(111) films on Si(110) by magnetron sputtering: orientation and twin growth

Abstract Cu epitaxial films were grown on H-terminated Si(110) and Si(111) substrates by magnetron sputtering. The epitaxial orientation of the Cu films and microstructural characteristics were studied by X-ray diffraction, including the conventional θ –2 θ mode and pole figures, and transmission electron microscopy (TEM). The results of pole figure analysis show an epitaxial orientation relationship of Cu(111)//Si(110) with Cu[110]//Si[001] and Cu[110]//Si[001] which are twin-related. The TEM observations of the cross-sectional samples reveal that the Cu film contains a layered structure due to growth twins. The reason for twin formation is discussed.

Magnetic and structural properties of epitaxially grown FeTaN thin films

Epitaxial FeTaN films (∼1500 A) were grown as a function of nitrogen flow rate on epitaxial Cu(001) buffer layers (∼2000 A) on Si(001) single crystal substrates to investigate the effect of Ta and nitrogen on the magnetocrystalline anisotropy and magnetostriction. Detailed structural investigation by transmission electron microscopy and x-ray diffraction showed that the FeTaN films were epitaxial with the Pitsch orientation relationship of FeTaN(110)∥Cu(001) and FeTaN〈111〉∥Cu〈110〉, which allows four different in-plane variants to coexist in the film. It was found that the saturation magnetization did not change with nitrogen addition (∼1600 emu/cc) up to 2% lattice dilation. The values of K1 and λ100 of Fe decreased slightly (20% and 10%, respectively), while λ111 increased with increasing nitrogen content and eventually changed sign at ∼2% normalized lattice dilation. These results qualitatively agree with our earlier findings on (001) oriented FeTaN epitaxial films on MgO single crystal substrates. Also...

Frequency dependence of the transverse biased permeability in thin permalloy films

The frequency dependence of the transverse biased permeability μ’t(f ) has been measured up to 250 MHz in thin (0.044 μm) and thick (2.1 μm) unpatterned sputtered permalloy films with uniaxial anisotropy. In these films, the initial permeability along the hard axis can be described by the classical eddy current damping model assuming uniform rotation. For both films, μ’t at low frequency agrees reasonably well with Hoffman’s ripple model assuming appropriate values for the structure factor. In the thin film, μ’t(f ) is independent of frequency within experimental error up to at least 250 MHz. However, in the thick film μ’t(f ) decreases more rapidly with frequency than can be explained by classical eddy currents, when the transverse bias field HB is not very large compared to the net anisotropy field. The value of HB at which μ’t(f ) reaches a maximum amplitude is also found to increase monotonically with increasing frequency, also inconsistent with simple eddy current predictions. It is suggested that th...