G. Gorman

Magnetic and structural properties of Co/Pt multilayers

Abstract The magnetic properties of Co/Pt multilayers, in particular anisotropy and coercivity, are very sensitive to the Co layer thickness and less dependent on the Pt layer thickness. Such dependence is illustrated and discussed for e-beam evaporated Co/Pt multilayers of various Co and Pt thicknesses. It is shown that the largest perpendicular anisotropy occurs for Co layer thickness of 1–2 monolayers. The magnetic anisotropy of Co/Pt multilayers also strongly depends on the crystallographic orientation. The largest perpendicular magnetic anisotropy was obtained for Co/Pt multilayers with Pt(111) parallel to the film plane. This was demonstrated in both evaporated and sputtered polycrystalline multilayers, as well as in molecular beam epitaxy (MBE) grown Co/Pt(111) superlattices. By contrast, MBE grown 3.7 A Co/16.8 A Pt(100) multilayers show in-plane anisotropy, and 3.7 A Co/16.8 A Pt(110) multilayers exhibit very strong anisotropy within the film plane. These observations suggest that the magneto-crystalline anisotropy plays a key role in the magnetic anisotropy of these structures. Significantly enhanced effective magnetization was observed for Co/Pt multilayers with ultrathin Co layer.

Longitudinal media for 1 Gb/in/sup 2/ areal density

Media with low noise at high transition density that demonstrate satisfactory recording performance at an areal density, of 1 Gb/in/sup 2/ when combined with dual-element (magnetoresistive read/inductive write) heads have been fabricated. A media structure of C/CoPtCr/Cr was utilized over a range of magnetic parameters: coercivity approximately=1600-1800 Oe, remanence-thickness product approximately=0.7*10/sup -3/ emu/cm/sup 2/, and coercive squareness approximately=0.7-0.8. Media noise reduction was accomplished by optimizing the film-growth characteristics to reduce intergranular exchange coupling in the magnetic layer. The low-noise characteristics of the media are manifested in their low transition jitter values, 5 nm for 3- mu m track width, and the absence of supralinear increase in media noise power with linear density up to 3000-3500 fc/mm. The -6-dB rolloff densities are in the range 4000-5000 fc/mm. Overwrite values are typically better than 40 dB. Microstructural analysis indicates that the reduced transition noise of the present media is due to physical separation of the grains in the magnetic films, which reduces the exchange coupling between the magnetic grains. The reduced coercive squareness of the low-noise media degrades the overwrite performance and is also expected to decrease the linear density resolution of the media. >

Improved exchange coupling between ferromagnetic Ni‐Fe and antiferromagnetic Ni‐Mn‐based films

Dc magnetron sputtered Ni‐Mn and Ni‐Mn‐Cr films are demonstrated to exhibit strong and thermally stable antiferromagnetism, as well as high corrosion resistance. For a 25.2 nm thick 53.3 Ni‐46.7 Mn (in atomic percent) film deposited on top of a 28.5 nm thick 81 Ni‐19 Fe film, a unidirectional anisotropy field (HUA) of 120.6 Oe is obtained at room temperature after annealing in vacuum. The equivalent interfacial exchange coupling energy (JK) is 0.27 erg/cm2, three times higher than that of bilayer Ni‐Fe/50Fe‐50Mn films. This strong exchange coupling appears correlated with the presence of an antiferromagnetic θ (NiMn) phase with a CuAu‐I‐type ordered face‐centered‐tetragonal structure. The blocking temperature, at which the exchange coupling disappears, is higher than 400 °C. The Cr addition to the Ni‐Mn film dilutes the exchange coupling, but the JK for the Cr content ≤10.7 at. %, is still higher than that of the Ni‐Fe/Fe‐Mn films. Both Ni‐Mn and Ni‐Mn‐Cr films exhibit corrosion behaviors much better than...

Magnetic and magneto-optical properties of cobalt-platinum alloys with perpendicular magnetic anisotropy

Co1−xPtx alloys with Pt contents in the range 0.45≤x≤0.9 show sizable perpendicular magnetic anisotropy, 100% perpendicular remanence and coercivities in the range 160 kA/m. Thin films of this material are grown by electron beam evaporation onto fused silica or Si, at substrate temperatures between 150 and 350 °C. Spectroscopic investigations of the polar Kerr rotation show a significant enhancement of the Pt related UV peak. A comparison of the static signal levels R×(θk2+ek2)1/2 of Co/Pt multilayers and alloys shows an overall 50% enhancement in the case of alloys. Curie temperatures around 200 °C are observed for Co∼22Pt∼78 compositions. These properties, together with the potentially high chemical stability and ease of manufacturing make Co1−xPtx alloys very attractive materials for short wavelength magneto‐optic recording.

Crystallography and microstructure of Tl-Ca-Ba-Cu-O superconducting oxides

We report on the crystallography and microstructure of six oxides in the Tl‐Ca‐Ba‐Cu‐O system with nominal compositions Tl1Ba2Cu1O5, Tl1Ca1Ba2Cu2O7, Tl1Ca2Ba2Cu3O9, Tl2Ba2Cu1O6, Tl2Ca1Ba2Cu2O8, and Tl2Ca2Ba2Cu3O10. The structures consist of one, two, or three Cu perovskite‐like units sandwiched between Tl‐O monolayers or bilayers. The predominant defects in the crystals with bilayer and trilayer Cu perovskite‐like units are stacking faults that produce local intergrowths of related structures. The density of stacking defects in these oxides correlates with changes in the superconducting transition temperatures.

Evaporated CoPt alloy films with strong perpendicular magnetic anisotropy

CoPt alloy films with large perpendicular magnetic anisotropy, perpendicular coercivity, and saturated perpendicular remanence are reported. These films were fabricated by e‐beam evaporation at substrate temperatures near 200 °C and above. Well‐(111)‐textured Pt underlayers are shown to dramatically increase the perpendicular magnetic anisotropy of CoPt alloy films. The large perpendicular magnetic anisotropy is shown to be strongly related to good CoPt(111) texture, and not to the ordered tetragonal Co50Pt50 phase.

Role of atomic mobility in the transition noise of longitudinal media

The relationship between grain growth morphology and the transition noise of high-density CoPtCr media on Cr underlayers is examined. The growth morphology is shown to depend on the sputtering pressure, substrate bias, and substrate temperature. Development of isolated magnetic grains is promoted when the mobility of the sputtered atoms is reduced, i.e. at high sputtering pressure, low substrate temperature, and no substrate bias. As the magnetic grains become more isolated, the media transition noise is significantly reduced, accompanied by a simultaneous reduction in the coercive squareness. This indicates that the transition noise is primarily governed by the intergranular exchange coupling among the magnetic grains, which can be optimized by controlling the grain growth morphology. The microstructural features of the decoupled media correspond to the zone I structure in J.A. Thorntons (1986) microstructure zone diagram. >

Dependence of magnetics, microstructures and recording properties on underlayer thickness in CoNiCr/Cr media

The effect of Cr underlayer thickness on the magnetic, microstructural, and recording properties of sputtered CoNiCr media is reported. Cr thickness was varied from 100 to 2000 AA while the magnetic layer was maintained in the range of 260-300 AA. Measurements using a vibrating sample magnetometer show a monotonic enhancement of coercivity from 600 to 1500 Oe with increasing Cr thickness. Media noise was measured as a function of transition density using a spectrum analyzer. The media noise power at 2400 flux changes per millimeter decreased by a factor of about 10 with the increase in Cr thickness. This reduction is accompanied by a reduction in the coercivity squareness and the development of granular features in CoNiCr grains growing on the columns of the Cr underlayer. These features are consistent with a reduction of exchange coupling among CoNiCr grains. >

Modification of zirconia film properties by low‐energy ion bombardment during reactive ion‐beam deposition

The effect of low‐energy ion bombardment on the structure and properties of zirconia films deposited by reactive ion‐beam process is investigated. Bombardment of 100‐eV Ar+ during film growth is shown to induce a substantial relaxation of the residual stress as a result of structural modification by the increased mobility of adatoms. Concurrently, the oxygen gettering capability, or film stoichiometry, is improved by the enhanced diffusion of oxygen on substrate surface. The structural change by thermal annealing, up to 600 °C, demonstrates that fine‐grained (200–400 A) cubic zirconia can be stabilized down to room temperature without alloying stabilizers. The impingement of low‐energy Ar+ during film growth results in an as‐deposited film microstructure which promotes the growth of the cubic‐phase crystallites upon post‐deposition annealing as well as the texturing of film plane into (111) orientation. The refractive index and optical transmission of the zirconia films are shown to be dependent predomina...

Phase stability limits of Bi2Sr2Ca1Cu2O8+δ and Bi2Sr2Ca2Cu3O10+δ

We determined the phase stability limits of Bi2Sr2Ca1Cu2O8+δ and Bi2Sr2Ca2Cu3O10+δ in the temperature range 650–880 °C using a solid‐state electrochemical technique. These phases decompose by incongruent melting above ∼790 °C, whereas they decompose by a solid‐state reaction at lower temperatures. The solid‐state decomposition reaction is reversible for Bi2Sr2Ca1Cu2O8+δ, but not for Bi2Sr2Ca2Cu3O10+δ.