Search

We describe a new [Ni.sub.5][Al.sub.3] underlayer for high-density longitudinal magnetic recording. The [Ni.sub.5][Al.sub.3] underlayer has the FCC derivative [Ga.sub.3][Pt.sub.5] structure. The [Ni.sub.5][Al.sub.3] (221) plane has good lattice match with the CoCrPt (10 [bar]1 0) plane. In addition, unlike the NiAl (112) plane, the [Ni.sub.5][Al.sub.3] (221) plane has the lowest surface energy. Hence, the [Ni.sub.5][Al.sub.3] thin film has a strong (221) texture and can induce CoCrPt (10 [bar]1 0) texture. The microstructure and magnetic properties of the CoCrPt-[Ni.sub.5][Al.sub.3] thin films are reported and discussed. Index Terms--Co alloy magnetic film, epitaxial growth, lattice match, longitudinal magnetic recording thin film, NiAl underlayer, [Ni.sub.5][Al.sub.3] underlayer.

Nanocrystalline FeCoB exhibiting a saturation magnetization of ~ 2.2T is examined. The film stress increases from compressive to tensile with a critical pressure of ~ 12 mTorr with the increase in pressure.

It has been established that Ag underlayers, with a slightly bigger unit cell than FePt, both prompt epitaxial growth of the FePt films and reduce the FePt ordering temperature. The larger the contraction of the FePt unit cell along the plane normal, the larger the tendency for the L1(sub 0) FePt phase to form.

The exchange coupling between ferromagnetic Ni(sub 81)Fe(sub 19) and antiferromagnetic (AF) Pt(sub x)Mn(sub 1-x) films prepared by rd and dc magnetron sputtering is investigated. The exchange bias was found to depend on the texture and film composition of the gamma-PtMn layers.

Highly oriented NiFe films were grown on HF etched Si substrates using sputter deposition. The epitaxial growth of the films were induced using the Ag and Cu underlayer depositions on Si substrates. X-ray diffraction spectra and transmission electron microscopy are used to determine the orientation relationships between NiFe, Cu and Ag. It is shown that soft magnetic properties exist in NiFe films.

A study was conducted to analyze the influence of platinum interlayers on the magnetic and crystalline structural characteristics of BaM films. A mechanism that explains the impact of the interlayers in improving the perpendicular anisotropy was discussed. The films were deposited by radio frequency diode sputtering in a Leybold Z-400 sputtering system. Experimental results indicated that increases in coercivity correlated with a weakening of magnetostatic interactions among the BaM grains.

A study was conducted to analyze highly oriented perpendicular cobalt-alloy media on Si(111) substrates. The orientation relationship was obtained by x-ray pole figure measurements. Experimental results indicated rocking curve measurement data supporting improved c-axis orientation of the cobalt alloy. Findings also showed that the magnetic characteristics of the films were enhanced by introducing single crystal templates.

A CoCrTa intermediate layer was added between a CoCrPt recording layer and a NiAl underlayer. CoCrPt (1010) texture improves and the in-plane coercivity increases using this medium structure. The effects of substrate bias on film texture and coercivity were studied. Pt concentration and lattice constant for CoCrPt were also characterized as functions of the bias voltage. Index Terms - Co, lattice match, NiAl, substrate bias.

An improved CoCrPt thin film medium for longitudinal magnetic recording which has a coercivity significantly greater than prior CoCrPt thin film media was investigated. A CrMn alloy underlayer was used, instead of the conventional Cr underlayer. A coercivity value of 4280 Oe was easily reached in a CoCrPt film on a 50 nm thick CrMn underlayer as compared to 2810 Oe with a pure Cr underlayer. It was found that the coercivity increase due to the Mn addition was realized if the substrates were preheated before the sputtering. Grain boundary interdiffusion of Mn from the underlayer to the magnetic layer may be the cause for the coercivity increase. Index Terms - Coercivity, CoCrPt, interdiffusion, CrMn, underlayer.

The thermal activation volume and the magnetic switching volume were measured in c-axis uniaxially in-plane oriented barium hexaferrite thin film magnetic recording media. Excellent agreement among the experimental data obtained independently from the magnetic viscosity measurements and the measurements of the time dependence of coercivity implies that the thermally driven process is the cause of both phenomena. The presence of incoherent switching during magnetization reversal is indicated by the in-plane angular dependence of coercivity and is believed to cause the much smaller activation volume and switching volume than the grain size as determined from a TEM micrograph.

Barium hexaferrite thin films deposited by rf magnetron sputtering have been made which exhibit saturation magnetization 90% of that of bulk single crystals, whereas the perpendicular uniaxial anisotropy is only 60% of that of the bulk. X-ray diffraction spectra suggest good c-axis orientation perpendicular to the film plane. However, M-H hysteresis loops show a fairly large in-plane hysteresis. Scanning electron microscopy and transmission electron microscopy show that the films are made of a mixture of platelet- shaped grains and acicular grains. Microdiffraction studies in a transmission electron microscope indicate that the platelets have their c-axis oriented perpendicular to the plane and that the acicular grains have c-axis orientation in the plane. Preferential grain growth in the basal plane of the crystal is believed to be responsible for these grain geometries. Because the platelets occupy a much larger volume of the film than the acicular particles, there is a preferential c-axis orientation perpendicular to the film plane.

The magnetic properties and micro-structural characteristics of CoNiCr/Cr films with thin Cr underlayers prepared on both single crystal Si and glass substrates are discussed. It is found that {200} crystallographic texture is easily obtained for Cr films prepared on Si at room temperature. Substrate bias during the Cr deposition, however, changes the Cr {200} texture to {110}. Substrate bias during the CoNiCr deposition degrades the texture of the Cr underlayer.

The effect of substrate bias on magnetocrystalline anisotropy ([K.sub.u]) of continuous [Co.sub.1-x][Pt.sub.x] alloy films with increasing Pt content is analyzed. The stacking fault (SF) density and the fcc content are reduced in the biased samples and these improvements in structural defects have helped in increasing [K.sub.u] in magnetic thin films.

The recording properties of CoCrPt thin films sputter-deposited on polymeric substrates at room temperature were determined. The interaction between grains appears to be the result of insufficient elemental segregation due to the low temperature deposition.

The possibility of using sendust (FeAlSi) as the soft magnetic underlayer for hexagonal barium ferrite (BaM) and strontium ferrite (SrM) was studied. Sendust films were found to retain their soft magnetic properties with a rapid thermal anneal (RTA) at 800 C for 60 s, which is necessary to crystallize the as-deposited amorphous BaM and SrM films. Several film structures with sendust films as the soft underlayer were studied and compared. Strong hcp (001) texture and bcc (110) texture were obtained on the BaM(SrM)/Pt/buffer/FeAlSi/Si multi-layer structure films, as indicated by the strong hcp (006), (008) and (0014) reflections for BaM(SrM) layer and bcc (110) reflection for the sendust underlayer from X-ray diffraction measurements. Index Terms--Barium ferrite, multi-layer, sendust, soft underlayer, strontium ferrite, textured growth.

Post-deposition rapid thermal annealing (RTA) was performed on the Cr-less Co20at%Pt alloy with a Mn diffusion layer on top. A Ku value of about 8 x [10.sup.6] erg/[cm.sup.3] was obtained for the as-deposited film and it decreased only up to about 10% after annealing. The high intergranular exchange coupling of the as-deposited CoPt film was suppressed by RTA and the coercivity increased dramatically from about 2200 to 6000 Oe. The energy-filtered TEM plane-view images showed depletion of Co and aggregation of Mn at the CoPt grain boundaries. This is a direct evidence supporting preferential diffusion of materials from adjacent layers into magnetic grain boundaries. Index Terms--Annealing, anisotropy, CoPt, Mn, segregation.

Stacking faults in (1010) unicrystal Co and Co-alloy thin films have been analyzed by the electron diffraction technique. As predicted no diffraction contrast of stacking faults could be observed when the beam is parallel to the [1010] direction. However, both by plan-view TEM observation and electron diffraction 4 along the [1120] direction reveal that the stacking fault density in biased pure Co (1010) thin films is much lower than that in unbiased ones. The addition of Cr in Co films significantly reduces stacking fault density whereas the addition of 8at% Pt leads to a considerable increase in stacking fault density. Our results show that stacking faults in Co thin films significantly, and negatively, affect the anisotropy energy density and its temperature dependence. Index Terms--Anisotropy, Co-alloy thin films, electron diffraction, magnetic recording, stacking faults, TEM.

CoCrPtTa/Ti bilayer thin films have been sputter deposited onto both glass and Al substrates under high sputtering rate in a manufacturing environment. From microstructure and magnetic property studies, it is found that Cr segregation and stacking fault density are the two major issues in obtaining high quality perpendicular media. (0002) texture orientation spread and c lattice parameter remain almost constant within the variation range of the deposition parameters, though there is a small distinction between the media on glass and those on Al substrates. Index Terms--Co-alloy, magnetic properties, microstructure, perpendicular media, sputtering rate.

40 nm thick CoPt and FePt films were prepared on oxidized Si substrates with 10 nm MgO underlayers. The maximum coercivity ([H.sub.c]) for CoPt films was found to be ~ 10 kOe after annealing at 700 [degrees] C for ~ 20-30 minutes (min). Structural analysis showed a significant amount of FCC phase as well as the ordered [L1.sub.0] phase in these films. FePt films showed an abrupt increase of ordered volume fraction and [H.sub.c] in the initial stage of annealing and predominance of the tetragonal [L1.sub.0] phase after 10 min. at 700 [degrees] C. The maximum [H.sub.c] reached ~ 16 kOe after annealing at 700 [degrees] C for more than 20 minutes. Dark field (DF) images of the annealed CoPt films showed individual grains which exhibited a possibility of several variants or disordered phase with dimensions similar to the exchange correlation length, [b.sub.cm]. The temperature dependence of [H.sub.c] seems to indicate a weak pinning mechanism in the highly ordered FePt films. Magnetic force microscopy indicated a complex domain structure consisting of clusters with dimensions of several hundred nanometers. Index Terms--Atomic ordering, coercivity mechanism, Copt and FePt, thin films.

The effects of a Pt underlayer and a Pt interlayer on the textured growth of the sputtered strontium ferrite (SrM) films were investigated. The structural and magnetic properties of SrM films on the Pt underlayers were compared with SrM films on thermally oxidized Si substrates. It was found that much better (OOl) texture was obtained on the films with Pt underlayers, as indicated by the strong (006), (008) and (0014) reflections from X-ray diffraction (XRD) measurement. A Pt interlayer was also found to further improve the (OOl) texture. Index Terms--Strontium ferrite, SrM, Pt underlayer, Pt interlayer, textured growth.

The effect of annealing on the exchange bias in [Ni.sub.81][Fe.sub.19]/[Cr.sub.50][Mn.sub.50] bilayers was investigated. A large increase of the exchange field and coercivity was observed in the samples annealed at temperatures higher than 310 [degrees] C. The annealing causes the Mn atoms in the [Cr.sub.50][Mn.sub.50] layer to diffuse into the [Ni.sub.81] [Fe.sub.19] layer and form an antiferromagnetic NiFeMn phase, which coats on the [Ni.sub.81] [Fe.sub.19] grain surface and contributes to the improvement of exchange bias. An increase of interface roughness due to the Mn diffusion also results in the exchange bias enhancement. The enhanced exchange field and coercivity were explained by the reversible and irreversible motions of NiFeMn moments of the inhomogeneous grains. Index Terms--Exchange bias, antiferromagnet, magnetic film, thermal annealing.

The effects of stoichiometry factor n on the magnetic and structural properties of perpendicular barium ferrite thin films with composition of BaO [multiplied by] n([Fe.sub.2][O.sub.3]) were systematically investigated. Within the range 2.2 [is less than] n [is less than] 6, the c-axis for barium ferrite thin films can be oriented perpendicularly by the use of Pt underlayer and with optimized processing conditions. Perpendicular c-axis orientation becomes worse as n decreases from 6 to 2.2. The average grain size was greatly reduced from about 2000 [Angstrom] to 300 [Angstrom] with the decrease of n. The decrease of the grain size can be related to the existence of nonmagnetic phase Ba[Fe.sub.2][O.sub.4], which was observed by X-ray diffraction. Index Terms--Barium ferrite, perpendicular c-axis orientation, stoichiometry factor, thin film media.

Polycrystalline MgO underlayer films lead to different preferred orientations of [L1.sub.0] CoPt and FePt films after the annealing process, depending on the thickness of [L1.sub.0] films. [L1.sub.0] films with a thickness greater than 20 nm revealed mostly [L1.sub.0] [100] fiber texture and consequently in-plane anisotropy as determined by magnetic hysteresis. Strong perpendicular anisotropy due to the [L1.sub.0] [001] fiber texture was obtained for thicknesses below 10 nm. The [Delta]M curve showed strong intergranular exchange coupling. The angular variation of coercivity showed the possibility of both domain wall motion and a rotational mechanism of magnetization reversal. Index Terms--CoPt, FePt, in-plane anisotropy, perpendicular anisotropy, recording media, thin films.

Quad-crystal Co-alloy/Cr/Ag thin film media were epitaxiaily grown on hydrofluric acid etched S1(111) single crystal substrates by sputter deposition. The orientation relationship was studied by x-ray [Theta]/2[Theta] diffraction and pole figure [Phi]-scan, and it was determined to be Co(1011) || Cr(110) || Ag(111) || Si(111). The Ag layer contains two twin-related orientations of grains. Cr grows with three variants of grains on the Ag(111) layer. Since Co(1011) contains grains with four possible easy axis directions when grown on each Cr variant, the quad-crystal media consist of grains with twelve easy axis directions and exhibit nearly isotropic in-plane magnetic properties. Index Terms--epitaxy, magnetic media, Co, Cr