Thomas Young Chang

Deconvolution of magnetic force images by Fourier analysis

A novel technique which allows the true magnetic charge distribution of a sample to be obtained from a raw MFM image by deconvolution is presented. The formation of magnetic force microscopy (MFM) images can be considered as a convolution of the tip response function and the divergence of the sample magnetization. The key element in this method is the tip response function, which contains the information about the magnetic and geometric properties of the tip. This tip response function is obtained by imaging the flux emanating from the end of an ultranarrow single-domain nickel strip which approximates a point magnetic charge. An MFM image of recorded bits obtained with the same tip is deconvolved utilizing Fourier transformation methods. By this approach, the deconvolved image becomes tip independent and it is possible to achieve spatial resolutions as small as the width of the Ni strip, which can be 10 nm wide. >

Method for investigating the reversal properties of isolated barium ferrite fine particles utilizing magnetic force microscopy (MFM)

The reversal properties of isolated barium ferrite recording particles with Co‐Ti substitution (BaFe12−2xCoxTixO19) are studied by a newly developed magnetic force microscopy (MFM)‐based technique. The size dependence of the switching field on particles with diameters ranging from 30 to 80 nm were investigated. A decrease in the switching field was observed, which corresponds to a decrease in the particle diameter below 50 nm. This indicates thermally assisted switching in small size particles. As the diameter increases, the switching field reaches a maximum at 55 nm then sharply decreases. An atomic force microscopy (AFM) profile of the particle’s thickness shows that the aspect ratio variation among these particles cannot account for the observed difference in the switching field. Thus, it is concluded that incoherent reversal is occurring in particles with diameter greater than 60 nm.

Angular dependence measurement of individual barium ferrite recording particles near the single domain size

The switching field angular dependence measurement of individual barium ferrite recording particles with sizes ranging from 55 to 75 nm in diameter were measured via magnetic force microscopy technique. These experimental measurements were then used as a basis to investigate their nucleation mechanism and intrinsic switching modes. Our findings indicate that the effects nonuniform doping of Co‐Ti can significantly affect the easy axis nucleation field and the switching mode.

Beyond 10 Gb/in/sup 2/: Using a merged notched head (FIB-defined writer and GMR reader) on advanced low noise media

We demonstrated recording performance at greater than 10 Gb/in/sup 2/ with data rates up to 25 MB/s, using a single combined write and read head (Merge Notched head).

Modeling Assessment Of The Side Writing Properties Of A Notch Write Head.

The side writing properties of a notch write head is studied via 3-D finite element method modeling. The head field properties are characterized by the erase width, track edge write gradient, and edge transition shift position. The calculated head field of the notch head are compared to the calculated values for a trimmed and merged head. The results show a significant decrease in the erase width at small notch depths of less than 1 gap length. However, the improved edge transition profiles associated with the trimmed head are not realized until the notch depth exceeds approximately 2 gap lengths.

Narrow track recording characteristics in thin film media

In this paper, we report a combined spin-stand measurement and micromagnetic simulation study on narrow track recording characteristics in thin film media. It is found that the onset recording density of nonlinear partial erasure is determined by intertransition percolations near the track edges where the head field gradient is poor. Trimming into the shared pole in merged MR/thin film heads is necessary for performance at both high linear and high track densities. Increasing head field magnitude with respect to medium coercivity increases the width of erase band but not the actual transition track width. When the head is skewed, the edge field overwrites on-track transitions, resulting in a reduction of effective transition track width. The trimming of the shared pole in merged MR/thin film heads can significantly reduce this edge overwrite effect. It is suggested that servo writing schemes should be modified to take into account the phenomena described in this paper.

Erase band and transition charge-model and MFM

The three-dimensional magnetic vector field for a magnetic recording head with unequal pole width is used as an input to a two dimensional extension of the Williams Comstock model to calculate transition charge, erase band widths, and to simulate magnetic force microscope images. Modeling results are compared to MFM images.

Effects of nonuniform substitution on the reversal process of individual barium ferrite recording particles

Micromagnetic simulation is utilized to investigate the mechanism responsible for the sharp decrease with increasing particle size in the switching field observed from experimental measurements of isolated BaFe/sub 12-x/(CoTi)/sub x/O/sub 19/ particles. Simulation results show that nucleation can occur at applied field values far below the intrinsic anisotropy field when the effect of nonuniform substitution of Co-Ti is considered. >

Affects of skew angle on the written-in base line shift (BLS) signal at high track densities

The track edge charge distribution responsible for the base line shift (BLS) in the MR readback waveform is studied through skew angle measurements. A model based on a finite element head field calculation and micromagnetic simulation is utilized to understand the track edge charge formation responsible for the BLS signal. The modeling results show that the spatial distribution of the dipole charge profile in the cross track direction becomes asymmetric when transitions are written at skew angles. This explains the observed asymmetry in the measured base line shift profile.