Charles F. Brucker

Thermal annealing effect on FeCoB soft underlayer for perpendicular magnetic recording

We study the noise performance of amorphous FeCoB soft underlayers (SULs) with radial magnetic anisotropy. 200 nm thick FeCoB films are sputter deposited and optionally postannealed for 8 s at different annealing powers. The correlation of SUL read-back noise with the magnetic and structural properties is studied using spin stand testing, in-plane magneto-optical Kerr effect measurements, magnetic force microscopy, and x-ray diffraction. The effects of annealing to achieve low read-back noise are examined. It is found that as-prepared films show large dc noise associated with stripe domains due to stress-induced perpendicular anisotropy. Thermal annealing reduces the internal stress and the films become magnetically anisotropic in the radial direction. The SUL-induced dc noise drops to the electronic noise floor. dc noise is found to decrease with an increase in annealing power until the films start to crystallize.

Measurements and modeling of soft underlayer materials for perpendicular magnetic recording

Measurements and modeling of soft magnetic underlayer (SUL) materials for perpendicular magnetic recording application are carried out. The process dependent magnetic properties of FeCoB, CoZrNb, and FeAlN SUL materials on glass and aluminum disk substrates are studied and correlated with spin-stand noise performance. The SUL-induced dc noise amplitude approaches the electronic noise floor for certain material combinations, e.g., FeCoB or CoZrNb on glass, when care is taken to relieve stress-induced perpendicular anisotropy by thermal annealing. Landau-Lifshitz-Gilbert micromagnetics, finite-element method calculations, and a micromagnetic recording model show that write field amplitude, write field gradient, and readback waveform are only slightly impacted by SUL moment in the 1-2 T range. Much more important are the head-to-SUL distance and the write head saturation moment. These results suggest that extremely high SUL moment may not be necessary, which can be leveraged to meet other key practical requirements such as corrosion resistance and manufacturability.

Perpendicular media: alloy versus multilayer

Properties and performance for alloy and multilayer perpendicular recording media designs utilizing a soft magnetic underlayer are compared. Among samples considered here, grain size and grain size dispersion are more highly refined for alloy media deposited at high substrate temperature, and are beginning to approach those now available in longitudinal recording. Multilayer media made at ambient temperature typically sacrifice film density and surface smoothness for interface quality. Although microstructural development and the manufacturing process for multilayer media are less mature versus alloy, multilayer media remain attractive due to their high anisotropy potential and the ease with which H/sub n/ and H/sub c/ can be controlled. For thermally stable alloy media made on a pilot production sputtering machine, a spin-stand areal density of 61 Gb/in/sup 2/ has been demonstrated at 350 Mb/s data rate with an on-track bit-error-rate reference level of 1e-6. Using the same media, a working perpendicular drive has been demonstrated at 32 Gb/in/sup 2/ and 500-800 Mb/s data rate.

High anisotropy CoCrPt(B) media for perpendicular magnetic recording

CoCrPt(B) media with high magnetic anisotropy have been fabricated at a thin magnetic layer thickness (10 nm) and a thin interlayer thickness (4 nm). The hard magnetic properties of the CoCrPt enable addition of boron, which aids to magnetically decouple the grains. These media are thermally stable and have an enhanced signal-to-noise ratio.

Experimental Effects of Laser Power on the Writability and Pulse Width in a Heat Assisted Longitudinal Recording System

In this paper the effects of increasing laser power on the writability and pulse width at half max (PW50) were experimentally measured on a longitudinal CoCrPt recording medium in a heat assisted magnetic recording system. The dynamic coercivity, quantified by spin stand measurements, was found to decrease linearly with laser power. Furthermore, it was found that careful optimization of laser power and write current are required to minimize the PW50. By choosing an optimal combination of write current and laser power it was possible to achieve a PW50 with heat assistance that could not otherwise have been reached. The results of this study help to establish the viability of heat assisted magnetic recording technology as a potential solution to density limits set by superparamagnetism.

Stripe domain formation in antiferromagnetically coupled FeCoX layers

We demonstrate that antiferromagnetic coupling can be used to suppress the formation of stripe domains in FeCoX layers. Antiferromagnetic coupling forces the magnetization in FeCoX layers to align antiparallel, which increases the magnetostatic energy of the stripe domain state in FeCoX∕Ru∕FeCoX. This increases the minimum critical thickness for which stripe domains are observed in both FeCoX layers of the FeCoX∕Ru∕FeCoX structure. The critical thickness scales with the strength of antiferromagnetic coupling, Jex, and almost doubles for antiferromagnetic couplings larger than about 2mJ∕m2.