The formation process of Zn-Ti doped Ba-ferrite particle was investigated by the x-ray diffraction technique, transmission electron microscopy and magnetic measurements. The effects of heating temperature T_h and the Zn-Ti substution x on microstructure and magnetic properties of BaFe_<12-2x> Zn_x Ti_x O_<19> particles with x=0.10-0.80 were studied. The temperature dependence of magnetic properties of these particles was measured.

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Thermal fluctuation in magnetization of longitudinal and perpendicular recording media was calculated using a Monte Carlo simulation method. Distribution of grain size in a medium increases the effect of thermal fluctuation in magnetization. Perpendicular recording is superior to longitudinal recording from thermal fluctuation point of view. In longitudinal recording, the effect of thermal fluctuation increases with increasing recording density, but in perpendicular recording the effect decreases with increasing recording density.

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This paper reports thermal stability of particulate media, which includes Co-Fe oxide, CrO_2,thick and thin MP tapes. Measuring the time decay of magnetization at room temperature, fluctuation fields were obtained as a function of the reversely applied field. It was clarified that the fluctuation field has a constant and minimum value when the reverse field is equal to coercivity. Based on this result, fluctuation fields for the four particulate tapes were measured at several environmental temperature, ranging from -75℃ to+100℃. It was clarified that the fluctuation field normalized by remanence coercivity increases as the environmental temperature increases for all tapes, indicating that becomes a good measure of thermal stability. Activation volumes were also reduced as a function of temperature.

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Skew angle and its effect to the head-disk integration for the Gb/sq-in areal density recording were studied systematically and reported. The results presented in this paper covers the skew angle effect on read/write performance, bit and track densities, landing zone tribology performance, off-track capability, noise and so on. High skew angle reduces the potential of bit density, increases the noise level, and increases the long term stiction in the take-off process in the landing zone. Isotropic and anisotropic media were studied on the skew angle effect. Media with different orientation ratio were used in the investigation.

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As recording density increases rapidly in recent years, high coercivity and low noise media became more an important issue in perpendicular as well as longitudinal recording media. Compare to CoCr, CoCrTa system is more effective in increasing coercivity by enhancing Cr segregation into column boundaries. There was no improvment in C-axis alignment in the case of CoCrTa when Ti underlayer was used. In the case of CoCrPt case, when Pt content is lower, coercivity was not improved and M-H curve showed more domain wall motion type reversal indicating rather strong magnetic coupling among columns. When Ta is added in CoCrPt, coercivity increased and M-H curve showed domain wall motion type behavior was reduced, which must be associated with Cr segregation to boundary by Ta addition.

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The magnetic properties change which was induced by a small amount of Ni addition into Cr underlayer and heat treatment in CoCrTa/CrNi thin film deposited by electron beam evaporator was investigated. The additional Ni element was found to be beneficial for increase in the coercivity of the film. The origin of coercivity increase was elucidated by crystal orientation and microstructure investigation using XRD and AFM respectively. It was found that the intensity of Cr (110) peak and the grain size were increased by Ni addition into the underlayer. The higher coercivity is related to the increase of Cr (110) peak in the underlayer and the reduction of Co (0002) peak in the magnetic layer. Coercivity was also increased after heat treatment above 400℃. The increase in coercivity may be resulted from the enhancement of Cr segregation by diffusion of Cr into the magnetic layer from underlayer.

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Recording properties of recently developed thin particulate Ba-Ferrite flexible disk media with perpendicular anisotropy were evaluated using MIG heads for hard disk drives with a small gap length and a narrow track width. The output, Ep, and the half output recording density, D_<50>, increased as the perpendicular squareness, SQ_⊥, of the media became large. The obtained highest D_<50> was 180 kFRPI and S_<pp>/N_<rms> was evaluated as high as 33 dB at 100 kFRPI for a 6 μm track width, which was higher than the high density metal particulate medium by 8 dB. Thus the areal density of more than 300 Mbit/in^2 would be expected for the system. Although increase of the medium noise was observed with increasing SQ_⊥, the noise would be reduced by the improvement in coating technology.

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Magneto-crystalline constants (Ku) and damping constants (α) of Co, CoCrTa, and CoCrPt thin films are determined by Torque and FMR measurements using well defined single crystalline thin films. (11^^-00) oriented single crystalline and (112^^-0) oriented bi-crystalline Co-based thin films are prepared on epitaxially grown Cr or Cr alloy underlayers on (110) and (100) MgO single crystal substrates. Ku values of Co, CoCr_<16>Ta_4,CoCr_<15>Pt_<12> thin films are determined to be 4.5×10^6,1.4×10^6,3.4×10^6 erg/cc, respectively. The effect of lattice mismatch between the magnetic layer and the Cr alloy underlayer on Ku value of CoCr_<15>Pt_<12> is systematically investigated. The α value of the Co and Co alloy thin films are determined to be ranging between 0.01-0.04. Recording resolution and noise characteristics of bi-crystalline CoCr_<15>Pt_<20> disk medium are also examined as a function of angle from the effective easy axis of the disk medium.

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With regard to practical structure of element, the transition process of domain structure during magnetizatization reversal in MR thin film sensor has been observed and investigated by wet and dry Bitter pattern technique. It is shown that the domain wall mergence and the wall-state transition during this incoherent magnetization rotation is closely related to Barkhauson jumps in the sensor, and also it is noted that the hooklike domain that appears at the link point of sensor and leads is involved in the irreversible transition.

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MR head is a device sensitive to temperature. The signal distortion related to mechanical contact between head and media is a special phenomenon to MR head. In this paper, a method which modifies the transfer function of data channel was investigated to eliminate the effect of thermal asperity of MR head in tape drive. The result shows that this method becomes a important, economic and effective way in addition to improving the MR head design.

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The two-dimension code is the newest robust recoding code. With much interest, is the 2D-PR4 (two-dimensional partial response class IV) code which is attractive in improving not only the recoding capacity and clocking ability, but also the required signal-to-noise ratio that is essential in obtaining the necessary bit error rate. This paper investigates and gives a comparison between this code and the QP code which is known as a powerful MSN code, and where both codes have the same code efficiency, 2/4.

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Magneto-Optical thin films with composition Tb-Fe-Co-Cr are coated on different substrates Al foil, Co-base and Fe-base amorphous ribbons. The thickness of M-O thin films is in the range from 200 nm to 1200 nm, which is sandwiched between two AIN layers with thickness 100 nm to prevent it from oxidation. The kerr loops of M-O films were measured with wavelength from 500 nm to 860 nm, and the peak applied field was 9KOe. The Kerr angles of M-O films deposited on Co-base and Fe-base amorphous ribbons are improved by a factor of 2.6 and 2.86 respectively at wavelength 780 nm. The Kerr angles of M-O films are enhanced by either Co-base amorphous ribbon or Fe-base amorphous ribbon markly. It can be considered as a magnetic image effect.

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Interface structures of Co/Pd and Co/Pt multilayers were modified by several different methods and the magnetic properties of these multilayers were investigated. It was found that the coercivity of Co/Pd multilayers could be enhanced to a great extent by increasing the sputtering pressure of Pd underlayer while Co/Pt films showed no significant increase of coercivity by sputtering pressure control of underlayer. Coercivity of Co/Pt films could be effectively increased by reducing the deposition rate of Pt sublayer, which was attributed to the enhanced pinning effect of domain wall motion. Argon ion bombardment to the multilayers turned out to decrease the coercivity as well as perpendicular magnetic anisotropy of both the multilayers.

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Magnetic force microscopy investigations were conducted on both conventional and overwriting 4X density magneto-optical media. Relationships between the geometric characteristics of recorded marks and the writing conditions were studied. On conventional MO media, isolated stable marks, which had size small enough to enable 16X density recording, were written. The residual marks on overwriting media were observed. For this kind of media, it was confirmed that the overwrite conditions need to be optimized for controlling the shape of marks which is crucial for PWM recording.

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In general, GeTeSb ternary alloy has been used as phase-change optical recording mrdium by using its differential reflectivity of crystalline phase or amorphous phase. In this experiment, GeTeSb film was deposited by using RF sputtering process. Thermal properties of GeTeSb film was measured with a differential sacnning calorimeter (DSC) under different heating rates. From DSC curves, the melting point of GeTeSb film is about 390℃ under different heating rates, while the crystallization temperature is varied under different heating rates. With heating rate increased from 10 ℃/min to 200 ℃/min, the crystakkization temperature is increased from 170 ℃ to 198 ℃. In real recording process of phase-change optical disk, the heating rate is much higher than 200 ℃/min. The three activation energy of crystalline phase respectively 1.86 eV, 1.93 eV, and 1.79 eV, can be obtained with Kissinger method. We can estimate the crystallization temperature in the recording process is around 230 ℃〜250 ℃ by numerical extrapolation method from DSC data. It is a useful method to predict the thermal properties of phase change recording medium. A detailed experimental data and analysis will be discussed.

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The upper dielectric layer of phase change disk affects markedly on recording characteristics. It is found that the threshold writing power decreases as the thickness of this layer increases. The erasibility is also related to the thickness of this layer. From the cycle test of erase and write, the disk structure in this article presented that the CNR value degrades about 1 dB when the cycle times increase one order of 10.

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