Maithri Rao

The effect of Pt interlayers on the magnetic and structural properties of perpendicularly oriented barium ferrite media

Perpendicular barium ferrite (BaM) films with Pt interlayers were successfully fabricated. The magnetic and structural properties of BaM films were compared with BaM films without Pt interlayers. It was found that perpendicular c-axis orientation was greatly improved for films with Pt interlayers. Perpendicular remanent squareness is increased, and the c-axis dispersion angle Δθ50 is decreased with Pt interlayers in BaM films. Also the coercivity was found to increase for films with Pt interlayers. A relative increase in perpendicular nucleation sites over in-plane and/or random nucleation sites contributes to the improvement in perpendicular c-axis orientation. The increase in coercivity may be explained by a weakening of magnetostatic interactions among BaM grains, due to magnetostatic isolation by the nonmagnetic Pt interlayers and the interdiffusion between Pt layers and BaM layers during high temperature ex situ annealing.Perpendicular barium ferrite (BaM) films with Pt interlayers were successfully fabricated. The magnetic and structural properties of BaM films were compared with BaM films without Pt interlayers. It was found that perpendicular c-axis orientation was greatly improved for films with Pt interlayers. Perpendicular remanent squareness is increased, and the c-axis dispersion angle Δθ50 is decreased with Pt interlayers in BaM films. Also the coercivity was found to increase for films with Pt interlayers. A relative increase in perpendicular nucleation sites over in-plane and/or random nucleation sites contributes to the improvement in perpendicular c-axis orientation. The increase in coercivity may be explained by a weakening of magnetostatic interactions among BaM grains, due to magnetostatic isolation by the nonmagnetic Pt interlayers and the interdiffusion between Pt layers and BaM layers during high temperature ex situ annealing.

Highly oriented perpendicular Co-alloy media on Si(111) substrates

CoCrPt/Ti/Ag films with the easy axes of the hexagonal-closed-pack Co grains perpendicular to the film plane were epitaxially grown on HF-etched Si(111) single crystal substrates by rf sputter deposition. The orientation relationship was determined by x-ray pole figure measurements and transmission electron microscopy to be CoCrPt(0001)[1010]∥Ti(0001)[1010]∥Ag(111)[112]∥Si(111)[112]. The magnetic properties of the CoCrPt films were greatly improved by introducing these single crystal templates. Rocking curve measurement showed a greatly improved c-axis orientation of the cobalt alloy. Highly oriented, high coercivity properties for perpendicular recording have been obtained.

Barium ferrite thin film media with perpendicular c-axis orientation and small grain size

Barium ferrite thin films with perpendicular c-axis orientation and small grain size (about 300 A) were successfully fabricated with careful control of sputtering conditions. The c-axis orientation of barium ferrite thin films is most sensitive to the oxygen partial pressure during deposition. All samples with oxygen gas during deposition have a random c-axis texture, as indicated by existence of both weak (00l) peaks and (106) peaks. All the samples without oxygen gas during deposition show only strong (00l) peaks, which indicate excellent perpendicular c-axis orientation. Transmission electron microscopy results show that oxygen gas promotes the growth of in-plane and/or randomly oriented grains. The effect of the Pt interlayer on the barium-rich films was also studied. The Pt interlayer was found to be very effective in improving c-axis orientation of barium-rich films. A relative increase in perpendicular nucleation sites over in-plane and/or random nucleation sites contributes to the improvement in p...

Highly oriented NiFe soft magnetic films on Si substrates

Highly oriented NiFe thin films have been produced via sputter deposition on HF etched Si substrates. Cu and Ag are used as underlayers to induce the epitaxial growth of NiFe films. The orientation relationships between NiFe, Cu, Ag, and Si have been determined by x-ray diffraction measurements and transmission electron microscopy. Magnetic properties have also been characterized.

CrPt3 thin film media for perpendicular or magneto-optical recording

The magnetic properties of CrPt3 L12 ferrimagnetic thin films have been studied. Films were produced by sputtering multilayers of Cr and Pt onto silicon nitride coated silicon substrates. The as-deposited films are nonmagnetic. An anneal at ∼800 °C results in ferrimagnetic behavior with a perpendicular easy-axis. X-ray diffraction and transmission electron microscopy (TEM) measurements show that (111) CrPt3 is the only crystalline phase present after annealing. Rocking curves with a full width at half maximum as low as 1.8° indicate good crystallographic orientation. Magnetic properties of the films vary with composition, annealing temperature and time, layer thickness, and sputtering conditions. The films exhibit large coercivities, Hc, that can be tuned in the range 1500–8000 Oe. Saturation magnetization, Ms, is typically 150–200 emu/cc. Squarenesses, S, as high as 0.99 have been found. A uniaxial magnetic anisotropy constant, Ku, of up to 8×106erg/cc was achieved. TEM micrographs show a 35 nm average g...

Thermal stability of ultra-thin Co recording media

Ultra-thin Co/Cr films were fabricated by RF diode sputtering. The highly exchange coupled Co grains were successfully isolated by post deposition processing. The microstructure was studied with TEM and a very small physical grain size was observed. The measurement of /spl Delta/M curves showed that the grain to grain interaction changed from positive to negative. Time dependent magnetic measurements showed significant thermal decay effects. It was also found that the use of CrMn underlayers instead of pure Cr further isolated the Co grains.

Effects of stoichiometry on the magnetic and structural properties of perpendicular barium ferrite thin film media

The effects of stoichiometry factor n on the magnetic and structural properties of perpendicular barium ferrite thin films with composition of BaO.n(Fe/sub 2/O/sub 3/) were systematically investigated. Within the range 2.2<n<6, the c-axis for barium ferrite thin films can be oriented perpendicularly by the use of a 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 /spl Aring/ to 300 /spl Aring/ with the decrease of n. The decrease of the grain size can be related to the existence of nonmagnetic phase BaFe/sub 2/O/sub 4/, which was observed by X-ray diffraction.

Microstructural origin of soft magnetic properties of sendust films prepared by N2 reactive sputtering

Sendust films were deposited using dc magnetron sputtering at room temperature in a mixture of Ar and N2 gas. The soft magnetic properties of the sendust films were, in general, improved with the addition of N2. The optimum soft magnetic properties were achieved when 6% N2 gas was used. Transmission electron microscopy studies showed that the sendust film without N2 contains average grain sizes of 200 nm; whereas the films with increasing N2 content contain increasing percentages of much smaller grains of 20 nm. The smaller grains have a random crystalline orientation with respect to each other. The cross-sectional morphological structures were studied using a scanning electron microscope. In the film without N2, power-law cone structures were observed. In the N2 containing films, needlelike morphological structures were formed. X-ray photoelectron spectroscopy studies on these films indicate that N2 included in the films reacts preferentially with Al to form AlN. Excess N2 may then react with Si, possibl...

Epitaxial growth of quad-crystal Co-alloy magnetic recording media

Quad-crystal CO-alloy/Cr/Ag thin film media were epitaxially grown on hydrofluric acid etched Si(111) single crystal substrates by sputter deposition. The orientation relationship was studied by x-ray θ/2θ diffraction and pole figure Φ-scan, and it was determined to be Co(1011) || Cr(ll0) || 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.

Highly Oriented Co Soft Magnetic Films on Si Substrates

Highly oriented NiFe thin films have been produced via sputter deposition on HF etched Si substrates. Cu and Ag are used as underlayers to induce the epitaxial growth of NiFe films. The orientation relationships between NiFe, Cu, Ag, and Si have been determined by x-ray diffraction measurements and transmission electron microscopy. Magnetic properties have also been characterized.