ALBERT

Notes: Iron films deposited by rf diode sputtering exhibited a robust, rotatable hysteresis loops with nearly perfect squareness; i.e., ∼100% of Ms rotates to any in-plane direction x, following the application of Hx(approximately-greater-than)Hc, and exhibits a stable uniaxial hysteresis for further variations in Hx. The rotatable anisotropy (RA) observed is highly reproducible on various substrates (glass, silicon, and alumina), and is unaffected by variations in; substrate temperature (to 300 °C), deposition rate (15–300 A(ring)/min), in-plane orienting magnetic fields (to 200 Oe), and annealing at temperatures to 370 °C in a large magnetic field (to 1.3 kOe). RA was absent only in films deposited in higher Ar pressures. © 1996 American Institute of Physics.

Notes: Among all the known magnetic materials with vanishingly small magnetostriction, alloys with the composition Co90Fe10 have the highest magnetization at 300 K. Despite this combination of useful properties, thin films of these alloys have been little studied. This study investigated the magnetic characteristics of Co90Fe10 alloy thin films deposited by rf diode sputtering. The hysteresis loops of nominal 1000-A(ring)-thick Co90Fe10 films deposited in ≈150 Oe planar field exhibited complex biaxiality. Two, orthogonal easy axis loops with different coercivities were observed. The direction corresponding to the hysteresis loops with the smallest (largest) coercivity are referred to as the soft (easy) axis. Dual hard axes were found at ±68° on either side of the easy axis. Similar biaxial hysteresis loops were observed in Co90Fe10 films deposited by sequential sputtering from pure Co and Fe targets on static or rotating substrates, and in films deposited from a Co90Fe10 alloy target on stationary substrates. The magnetization and resistivity of the sequentially sputtered films were 19.66 kG and 18.4 μΩ cm, while those deposited from the alloy target were 19.00 kG and 14.5 μΩ cm. The biaxiality was sensitive to a number of parameters which appeared to destabilize the soft axis state compared to the hard axis states. With increasing film thickness (to 3400 A(ring)), the biaxiality disappeared, and films deposited under similar conditions exhibited rotatable anisotropy. The biaxiality could also be reduced, and the coercivity increased, by increasing the magnetic bias applied during deposition. Films annealed at 370 °C became uniaxial when a 1.3 kOe field was applied parallel to the easy axis, and became isotropic when the field was parallel to the hard axis.The biaxiality was enhanced, and Hc reduced, by depositing 1000-A(ring)-thick Co90Fe10 films onto a 500 A(ring) 80Ni20Fe underlayer. In all cases, whenever the biaxiality was eliminated, the films exhibited a rotatable uniaxial anisotropy. The biaxiality of these films likely has its origin in the coupling of two uniaxial anisotropies as previously analyzed. The deposited films are highly polycrystalline. In addition, the symmetries of the planar magnetic state obtained were the same for crystalline and amorphous substrates. Thus, it is unlikely that either uniaxial anisotropy is due to magnetocrystallinity, but are probably induced. The experimental trends observed in the study can in principle be understood in terms of a two layer model in which a rotatable, stress induced uniaxial anisotropy in an underlayer, is exchange coupled to the field induced uniaxial anisotropy of an overlayer. In this model the complex biaxiality is modified by experimental parameters which modify the relative strength and coupling strength of these anisotropies. © 1996 American Institute of Physics.

Notes: Recent research has demonstrated that large amounts of hydrogen can be electrolytically incorporated in amorphous, compositionally modulated (CM) FeZr films. The first irreversible changes in the magnetic state of an electrolytically hydrogenated iron-rich amorphous alloy were observed. The hydrogen-induced changes in the magnetization were interpreted in terms of specific structural rearrangements. In this work, simultaneous measurements of the variations in the magnetization and mechanical properties of these films were measured as a function of hydrogen charging to further clarify the hydrogen-induced structure changes. The Young's moduli E and internal friction d of as-deposited, and as-hydrogenated CM Fe80Zr20 thin films were calculated from the displacements of a vibrating composite cantilever, measured using a laser heterodyne interferometer (LHI) having a displacement sensitivity of ∼0.01 A(ring). E and d were measured using the resonant frequency method. CM films with thickness 1390 A(ring) and modulation wavelength ∼10 A(ring) were deposited on glass cantilevers (5 mm long, 2 mm wide, and 150 μm thick) by sequentially sputtering (rf diode) elemental Fe and Zr targets.The samples were electrolytically hydrogenated for various times in 2 N phosphoric acid with a current density of 26.3 mA/cm2. The maximum change in magnetization of the film (from 71.5 to 551 emu/cm3) was observed after 5 min. During this time, E increased 18-fold from 535 GPa to 9.63 TPa. The unusually high Young's modulus of the as-deposited CM film is comparable to those previously observed in other CM films. The change is three times larger than the change in the E of carbon steel at the martensitic transformation, and nine times larger than the hydrogen induced increase in E of pure single crystals of iron. The d of the cantilever resonance decreased with hydrogenation, indicating that the incorporated H reduced the internal friction of the CM film. Preliminary analysis of the results indicates that the mechanical and magnetic changes can be interpreted in terms of similar atomic scale changes. Measurements on films with different CM wavelengths are in progress. © 1996 American Institute of Physics.

Notes: Recent research1 has indicated that ferromagnetic laminates are potentially useful in the design of integrated monolithic microwave integrated circuit (MMIC) devices operating at GHz frequencies. Laminates with n=10–50 insulated, uniaxial magnetic films can have large permeabilities and device fill factors, and are process compatible with monolithic integration. The effect of lamination disappears, however, for frequencies greater than the frequency of a dimensional resonance (DR) associated with the easy axis dimension of the laminated object.23 Thus, when the ferromagnetic resonance (FMR) occurs at a frequency greater than the DR, the FMR spectra of the magnetic films may be distorted or, possibly, not observed. The bandwidths of both the DR and the FMR will be significantly broadened, if either lies above the eddy current relaxation (ECR) frequency of the individual magnetic films. Prior models23 of the permeability of laminated objects were developed for magnetic recording head laminates operating at frequencies below 10 MHz. At these frequencies, the effects of FMR are negligible, and easy axis dimensions e〉1 cm are required to observe DR. In this work we modified our equivalent circuit model (ECM)3 to include the effects of DR, FMR, and the ECR in each layer. FMR spectra in the GHz frequency range, were computed for laminates with different dimensions, a variable number of different magnetic and insulating films, and a range of film thicknesses. A single domain, coherent rotational model was used to determine the layer permeability. The effect of the dc and rf shape demagnetizing fields of the laminated object on the FMR of the individual layers was included. The results show that the FMR spectra are shifted and distorted when the DR is near the FMR, and significantly broadened for insulator resistivities 〈1000 Ω cm and, as expected, when the FMR〉ECR. To eliminate DR in the GHz range, the laminate must have e〈100 μm.© 1997 American Institute of Physics.

Notes: Nanocomposite thin films with coexisting magnetic metal and magnetic nonmetal amorphous phases were synthesized by reactively sputtering CoFeSiB:O thin films with a large silicon (15 at.%), and varying oxygen concentrations. The microstructure, magnetization, and hysteresis loops were measured for films with resistivities near the metal–nonmetal transition. These data revealed that, below the metal–nonmetal transition, conductive transport was along the soft magnetic, metallic backbone of the percolation network; the nonmetal phase was a discontinuous, randomly distributed, hard magnetic oxide. The metallic resistivity and exchange anisotropy were both maximized in a nanocomposite with a resistivity at the metal–nonmetal transition. © 1996 American Institute of Physics.

Notes: This work investigated the effect of ion beam mixing on the magnetic and structural characteristics of Gd-Co multilayer films. Multilayer films with bilayer periods (BP) from 10 to 300 A(ring) were mixed by 150 to 300 keV Ar+ ion doses of 1016 cm−2. The magnetizations of the as-deposited multilayers were dominated by oxidation, and by the asymmetric redistribution of Co atoms. Ion beam mixing eliminated much of these effects, but the degree was strongly dependent on the layer thickness. The small BP films were completely mixed, with amorphous nanoparticles, but the large BP films contained small, microcrystals in an amorphous matrix due to incomplete mixing. The magnetic moment of ion beam mixed films were strongly dependent on the ion beam energy and the layer thickness. © 1996 American Institute of Physics.

Notes: Multilayered Co–B films with various bilayer periods (BP=TCo+TB, TCo=4×TB) and ratios of bilayer thickness were ion beam mixed with 150 keV 1016 Ar ions/cm2. The morphologies of both the as-deposited and the ion beam mixed films changed with BP. The ion beam mixed films exhibited amorphous structures, and the morphologies differed as a function of layer thickness in the as-deposited state. The morphological differences appeared to influence magnetic properties such as in-plane anisotropy and coercivity. Magnetization measurements revealed that the compositional inhomogeneities resulted in the anomalous extension of ferromagnetic composition range compared to melt-quenched films.

Notes: We have extended the stable amorphous phase of the Co1−xZrx system to 7〈x〈52 by compositionally modulating very thin (five to ten atomic layers) layers of Co and Zr by rf diode sequential sputtering from the elemental targets onto rotating, water cooled substrates. This extension was attributed to a stable, two-phase, hetero-amorphous state similar to that previously reported for Co/B layered structures (Ref. 1). The measured compositional variation of Ms of our Co/Zr layered structures indicated that, as expected, the composition of the stable Co-rich clusters in the heterogeneous state lies near the stable Co-rich eutectic of the CoZr system. The composition variation of the coercivity of the as-deposited Co/Zr structures was remarkably low (〈1 Oe) over the entire composition range. The uniaxial anisotropies of 15–30 Oe were reduced to ≈2 Oe by a combination of bias sputtering and rotating field annealing. Although they have reduced Ms, the permeabilities of the Zr-rich films are (approximately-greater-than)1200, and constant (to 10%) to ≈50 MHz. They also have high resistivities (≈190 μΩ cm), potentially increased hardness and stability, and could be useful for magnetic recording head applications.

Notes: Artificially layered structures have attracted attention because of their unique structural and magnetic characteristics. It has been reported that in these structures the anisotropic distribution of atomic pairs can play an important role in determining their magnetic anisotropy.1 Our previous work showed that the application of substrate bias in a rf diode sputtering system was effective in producing dense and stable amorphous compositionally modulated films (CMFs).2 In this work, we studied the interrelationships of the structural and magnetic properties of amorphous Tb-Fe CMFs deposited under various substrate bias conditions (0, −70, −90 V) in a multitarget rf diode sputtering system. Although considerable research has been conducted on the effect of ion bombardment during deposition on the film structure, it has been difficult to independently control the film structure and the composition in such experiments because of the preferential backsputtering of atoms.Accordingly, in this research we systematically prepared Tb-Fe CMFs by independently controlling the rf voltage ratio of both the Tb and Fe targets, thereby allowing the composition of the film to be held constant as the substrate bias was changed. In contrast to alloy films, atomic clustering was observed in ultrathin layered films and produced anomalous structural and magnetic property changes, e.g., a shift in the room-temperature compensation composition (25 at. % Tb for −70 V biased films and 23 at. % Tb for −90 V biased films), higher Curie temperatures, and an increased compositional range over which amorphous phase was stable. The atomic arrangements in layered films were modified by a variation of deposition parameters such as layer periodicity, substrate bias, and composition. Although all the bias-sputtered CMF films, except those with small Tb content (〈18 at. % Tb), had a dense and featureless amorphous structure, electron diffraction revealed significant differences in atomic short-range ordering for different Tb compositions. The results indicated that the magnetic moments of the Fe atoms in the CMF were increased by an enhanced pair ordering of like atoms produced by the alternate deposition of ultrathin layers. This result was consistent with the observed anomalies in magnetic properties.

Notes: Compared to single-layer films, CoZrNb/SiO2 multilayers with amorphous, soft magnetic films exhibit increased high-frequency response (to about 100 MHz) that is not understood. We studied single and multilayer films in this system and observed three distinct types of magnetic bias and frequency responses (phases I–III). The high-frequency responses of phase II and III films were reduced from that of phase I. Phase changes were produced in the single-layer amorphous CoZrNb films by varying the film thickness, and in double-layer (N=2) and multilayer (N〉2) films by varying the magnetic layer thickness. The phase boundaries in the former were shifted by magnetostatic coupling of the perpendicular component of M. These studies indicated that phase I films had uniform planar magnetizations, while phase II and III films had perpendicular components. The results are summarized in the form of a phase diagram (film thickness versus inverse film separation), which suggests that the frequency response of multilayer thin films is enhanced when the individual magnetic layers are sufficiently thin to insure a planar magnetization (phase I).