Gerardo A. Bertero

Optimization of granular double-layer perpendicular media

Optimized two types of granular, double-layer perpendicular recording media based on CoCrPtB and CoCrPtO alloy systems focusing mainly on signal-to-noise ratio (SNR) and thermal stability characteristics of the media. For the soft underlayer (SUL) portion of this study we compared NiFe, FeTaC, and FeAlSi films with and without lamination. Lamination of the SUL films resulted in marginal SNR improvement but was not effective in inhibiting the presence of magnetization domains. The CoCrPtB based media was found to have significantly lower noise than CoCrPtO, but its thermally stability is greatly compromised. On the other hand, the CoCrPtO media displayed negative nucleation fields and stable magnetization states even at DC-erased conditions.

Structure-property correlations in Pt/Co multilayers for magneto-optic recording

Abstract A series of Pt/Co (111)-oriented multilayer thin films were sputter-deposited under a number of deposition conditions to promote differences in the structure of the films. The defect density, grain boundary structure, layering and quality of texture were found to depend on the choice of sputtering pressure and gas, namely, Ar, Ar/Xe, or Xe. These differences were correlated to the magnetic and magneto-optic properties of the films. Of major interest were the effects of microstructure on the perpendicular magnetic anisotropy and magnetic coercivity. It is found that the observed coercivity correlates well with the grain boundary structure. The perpendicular magnetic anisotropy on the other hand is better correlated with the quality of the layering. The roles of the stacking defect density, quality of the (111) texture, and the effects of grain shape on the perpendicular anisotropy are discussed as well.

Low-noise CoCrPtO perpendicular media with improved resolution

CoCrPtO perpendicular media with coercivities greater than 6000 Oe, M/sub r//M/sub s/ equal to 1.0, and negative nucleation fields exceeding 3000 Oe were produced. The crystallographic, magnetic, and recording properties were optimized with respect to Ru interlayer and CoTaZr soft-underlayer thicknesses. Media with exchange decoupled magnetic grains as small as 7 nm with a narrow size distribution capable of supporting a linear density up to 720 kfci were produced. Thermal decay measured at 50 kfci at ambient temperature was less than 0.1%.

Fields and transforms for thin film heads

Analytical expressions for the vector magnetic fields and Fourier transforms associated with thin film heads are presented. These results are derived from accurate, approximate expressions for the surface field of an asymmetric thin film head determined from conformal mapping solutions. A 2D Greens function is integrated to yield exact analytic expressions for the fields, which are of no more complexity than the Karlqvist field approximations. In spite of their simplicity, these expressions accurately represent the fields at all corners, both at the gap and at the pole edges. These results are only approximate at spatial distances beyond the head edges and at wavelengths beyond about ten times the total head length. The Fourier transform of the surface field is also given in simple analytic form. As an example of the use of these expressions, it is shown how the effect of pole length to gap length ratio an pulse superposition can be easily estimated. >

Interface structure and perpendicular magnetic anisotropy in Pt/Co multilayers

Pt/Co multilayers sputter‐deposited in Ar and Xe ambients, and periodic multilayers composed of specific combinations of Pt, Pd, and Co layers, were grown to study the effects of energetic backscattered Ar neutrals on the interface structure. The effects were correlated with the magnetic and magneto‐optical properties with emphasis on the perpendicular magnetic anisotropy, K⊥. Films were characterized by high‐resolution transmission electron microscopy, x‐ray diffraction including grazing incidence geometry, and magnetic circular x‐ray dichroism techniques as well as by standard magnetic and magneto‐optic methods. It is found that the perpendicular magnetic anisotropy is extremely sensitive to the degree of intermixing, sharp interfaces yielding the largest anisotropy. The three to fourfold difference in K⊥ found between Ar and Xe sputtered films can be directly correlated to the magnitude of the orbital moment contribution 〈LZ〉 in the Co. This orbital contribution is found to be strongly sensitive to the...

(Pt/Co/Pt)/X multilayer films with high Kerr rotations and large perpendicular magnetic anisotropies

We have sputter‐deposited a series of (Pt/Co/Pt)/X multilayer structures with X=Pd,Ag,Cu displaying large Kerr rotations with improved perpendicular anisotropy and magnetic coercivity compared to the corresponding Co/X multilayers. In particular, Ar‐sputtered (Pt/Co/Pt)/Pd multilayers, with the Pt layer thicknesses corresponding to one atomic monolayer, present Kerr rotations of the order of 0.26°, perpendicular anisotropy energies of 33×106 ergs/cc (Co) or better, and magnetic coercivities as high as 8 kOe.

Origin of incoherent magnetic switching behavior in CoCrPt–SiO2 perpendicular magnetic recording media

Magnetic switching behavior for CoCrPt–SiO2 single layer media with oxygen contents (OCs) from 4% to 10% and recording layer thickness (tmag) from 2to27nm is investigated. Significant incoherent switching, caused by domain wall motion, and large activation volume are observed at tmag⩽6nm regardless of OC, consistent with nonuniform microstructure with less grain isolation at tmag=4nm. These results support formation of a highly exchange-coupled thin magnetic layer on top of Ru interlayer, which can explain the large difference between angular dependence of Hcr predicted by the Stoner-Wohlfarth theory and the experimental values.

Observation of microwave-assisted magnetization reversal in perpendicular recording media

This letter reports microwave-assisted magnetization reversal (MAMR) in a 700-Gbit/in2 perpendicular media sample. The microwave fields were applied by placing a coplanar waveguide on the media sample and feeding it with narrow microwave pulses. The switching states of the media grains were measured by magnetic force microscopy. For microwaves with a frequency close to the ferromagnetic resonance (FMR) frequency of the media, MAMR was observed for microwave power higher than a certain threshold. For microwaves with certain high power, MAMR was observed for a broad microwave frequency range which covers the FMR frequency and is centered below the FMR frequency.

Kerr rotations and anisotropy in (Pt/Co/Pt)/X multilayers

The link between interface sharpness and perpendicular magnetic anisotropy (K/sub /spl perp//) in Pt/Co multilayers has been exploited to yield enhanced magnetic anisotropy in related multilayer structures. These new multilayers consist of a (Pt/Co/Pt)/Pd stacking sequence where the Pt thickness is of just one atomic monolayer. The extra interfaces per period are introduced in areas where the spin polarization is still expected to be large thus resulting in extra magnetic anisotropy. K/sub /spl perp// as high as 5/spl times/10/sup 7/ erg/cm/sup 3/ was measured in Xe sputtered films with this new period. This idea was extended to (Pt/Co/Pt)X systems with X=Ag, Cu, Ni. A ten fold increase in K/sub /spl perp// is observed in these films compared to their respective Co/X counterparts. The Kerr rotation (/spl theta/K) as a function of photon wavelength is also greatly enhanced by the presence of the Pt monolayers. A strong dependence of /spl theta/K on the spacer element X in these systems is observed.

Ru/Ru-oxide interlayers for CoCrPtO perpendicular recording media

A novel Ru/Ru-oxide interlayer structure was investigated to improve intergranular decoupling in a magnetic layer. The effect of this interlayer on the microstructure, and magnetic properties of CoCrPtO perpendicular media is reported. By using a Ru-oxide layer on a conventional Ru layer, the interlayer grain size was 11 nm. The resulting vertical c-axis dispersion of the interlayer was less than 3/spl deg/ with no disruption in epitaxial growth throughout the Ru/Ru-oxide and Ru-oxide/magnetic layer interfaces. Grain clusters in the CoCrPtO magnetic layer were observed to match one-to-one with interlayer grains, and were well isolated from each other by nonmagnetic oxide phase grain boundaries. A high coercivity (over 6.9 kOe) and a nucleation field of -2.8 kOe were obtained with this Ru (26 nm)/Ru-oxide (2 nm) interlayer structure.