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ABSTRACT: The process of thermal switching and thermal activation volume of perpendicular recording media with dispersions of grain size have been analyzed using micromagnetic simulation with Voronoi lattice model. It was found that in media with smaller inter-grain exchange coupling w, almost all grains switch thermally alone, and the average activation volume langV<sub>ac</sub>rang does not depend on the applied DC reverse field significantly. While, in media with larger w, several neighboring grains switched simultaneously and langV<sub>ac</sub>rang increased with increasing reverse field, but not so much. It was also found that langV<sub>ac</sub>rang increased slightly with w until w reached some critical value, beyond which langV<sub>ac</sub>rang increased remarkably with w
IEEE Transactions on Magnetics 11/2006; · 1.36 Impact Factor
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ABSTRACT: The possibility of 300-500 Gbit/in<sup>2</sup> perpendicular recording using granular recording media with dispersions of grain size and separation has been investigated through micromagnetic simulation based on grain separated Voronoi lattice. It was found that sufficient values of signal to noise ratio and good thermal stability are obtained for optimal medium parameters. The results were basically similar to those for uniform grain size and separation. The medium noise does not change significantly when the dispersions are introduced. The design concept and obtaining calculation process of optimal large-grain-separation medium previously reported remain valid.
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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Magnetics Conference, 2000. INTERMAG 2000 Digest of Technical Papers. 2000 IEEE International; 05/2005
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ABSTRACT: The effect of the magnetic properties of the lower layer, of the antiferromagnetically coupled (AFC) media on thermal stability and the signal-to-noise ratio (S<sub>1F</sub>/N<sub>d2F</sub>) was studied using a Monte-Carlo simulation and the Langevin equation. Thermal stability was the highest when the largest M<sub>s2</sub> value was used within the limits of achieving antiferromagnetic coupling between the magnetic layers, and when the value K<sub>u2</sub> was less than the value of the upper layer. S<sub>1F</sub>/N<sub>d2F</sub> increased linearly with a decrease in the anisotropy field H<sub>k2</sub> at the rate of 0.5 dB per 100 kA/m.
IEEE Transactions on Magnetics 10/2002; · 1.36 Impact Factor
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ABSTRACT: Thermal stability in longitudinal thin film media was studied
using a Monte-Carlo simulation. As recording densities increase, the
signal decay ratios increase. The effect of the density is, however,
very small. Between two materials with identified thermal stability
factors 〈K<sub>u</sub>V〉/kT (where, K<sub>u</sub> is the
anisotropy constant, V is the volume of a grain, k is Boltzmann's
constant, T is the temperature, and 〈〉 means an average
value), the medium with smaller grains was found to be more stable
against thermal fluctuations. These phenomena are related to the
magnetic fields that are applied to grains in the media, which make the
magnetization stable against thermal fluctuation
IEEE Transactions on Magnetics 08/2001; · 1.36 Impact Factor
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ABSTRACT: The thermal activation volume in hard-disk media was investigated
through micro-magnetic simulation. It was found that the activation
volume should be obtained by using the time-dependent irreversible
magnetization (viscosity). The method using the total magnetization
including the reversible magnetization leads to a wrong dependence of
the activation volume on the field. The relationship between the
switching volume in a hard-disk medium and the activation volume is
described as a function of the exponent of the dynamic coercivity, the
switching field, and the anisotropy field
IEEE Transactions on Magnetics 08/2001; · 1.36 Impact Factor
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ABSTRACT: Magnetization-switching behavior was investigated in
high-data-rate hard-disk media through micro-magnetic simulation to
clarify the distinction between the gyromagnetics dominated scheme and
the thermodynamics dominated scheme in the dynamics of the switching. It
was found that the pulse-shape dependence of remanence coercivity
H<sub>cr</sub> and the anisotropy field H<sub>k</sub> dependence of the
switching-speed are caused by the gyromagnetic effect. The thermodynamic
effect plays a main role in the time-dependent H<sub>cr</sub> when the
pulse width is over 1 ns. On the other hand H<sub>cr</sub> in the
thermodynamic region decreases linearly with respect to the logarithmic
pulse width. The demagnetizing field from the write bubble causes
H<sub>cr</sub> to increase with the reverse DC erase (RDC) method in 10
or fewer “reptations”
IEEE Transactions on Magnetics 10/2000; · 1.36 Impact Factor
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ABSTRACT: The angle dependence of the attempt frequency f<sub>0</sub> has
been determined by assuming isotropic thermal excitation in the
anisotropic free energy around the easy axis of a single-domain
particle. The relationship between the logarithmic time and the
time-dependent remanence coercivity H<sub>cr</sub> was estimated. The
acquired equation agrees sell with the numerical calculation of the
Langevin equation. The conventional formula do not give the correct
relationship between H<sub>cr</sub> and K<sub>β</sub>(=Kv/kT)
because the exponent of K<sub>β</sub> depends on
K<sub>β</sub>. The estimated K<sub>β</sub> from Sharrock's
formula is 15% larger at K<sub>β</sub> of 100 and 5% smaller at K
<sub>β</sub> of 50. Bertram's formula is effective at K<sub>β
</sub> of 100 but brings 7% smaller estimation at K<sub>β</sub> of
50
IEEE Transactions on Magnetics 10/2000; · 1.36 Impact Factor
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ABSTRACT: We have investigated magnetization switching behavior in high-data-rate hard-disk media by micro-magnetic simulation. We found that the remanence coercivity measured by a short-pulse-field depended on the field-pulse shape. The time integration of external field over the remanent coercivity for a long-pulse-field, namely switching force integration (SFI), was an essential factor for the switching. We also found that the optimum writing field, H<sub>w</sub> must be increased by only 0.4 kA/m per MB/s independent of the linear recording density. Overwrite (OW) value decreased by 1 dB per percentage point of H<sub>w</sub> and did not depend on the data-transfer rate. The recording characteristics at high data transfer rates were not degraded if only a writing field of H<sub>w</sub> was applied to the film. The simulation results were consistent with the results of read/write experiments especially OW characteristics up to 80 MB/s.
IEEE Transactions on Magnetics 02/2000; · 1.36 Impact Factor
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ABSTRACT: Realistic recording conditions in longitudinal thin-film media at
high-frequency (up to 1 GHz) are investigated by a micromagnetic
simulation. It is found that the recording frequency should be set below
the characteristic frequency (1/2 Tr, where Tr is the rise time of the
writing head); optimum writing field intensity must be increased by 1.2
Oe per MHz at a linear density of 244 kFCI; and remanence coercivity
measured by a square pulse slightly increases up to 1 GHz when damping
constant is 0.03
IEEE Transactions on Magnetics 10/1999; · 1.36 Impact Factor
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MMM-Intermag Conference, 1998. Abstracts., The 7th Joint; 02/1998
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ABSTRACT: The magnetoresistive (MR) response of an MR sensor with shields to
a uniform applied field was calculated through a micromagnetic
simulation, and the results were compared with those from an MR sensor
without shields. A uniform longitudinal field, resulting from boundary
pinning by exchange-biased antiferromagnetic films, was applied to the
MR films of the two sensors. There are three differences between the MR
sensors with and without shields: first, the slope of the MR response
with shields near an applied field of zero is smaller than the slope of
the response without shields. Second, the response of the shielded MR
sensor has no subpeak, while the response of the unshielded MR sensor
has a subpeak. Third, the output of the shielded MR sensor hardly
decreases in a large field (1000 Oe), while the output of the unshielded
MR sensor quickly falls to a small value in a field of 300 Oe. These
differences are due to attenuated magnetic fields in the gap between the
two shields except near the air bearing surface (ABS)
IEEE Transactions on Magnetics 06/1997; · 1.36 Impact Factor
