H. Endo

Numerical Simulation of Switching Time of Magnetic Particle

The effects of magnitude and angle of applied field and the effect of Gilbert damping constant on switching time of a cubic particle with crystalline anisotropy at 0 and 350 K were investigated by using numerical simulation. The switching time decreases with increasing angle of applied field at 0 and 350 K. The switching time is proportional to (1 + α 2 )/α, when applied field is a few per cent larger than the Stoner-Wohlfarth switching field, and it is not proportional to (1 + α 2 )/α when the applied field is close to the switching field. When the applied field is almost oriented in the -z direction, t s is proportinal to 1/((H/H s ) - 1). However, when the field is applied in the direction larger than a few degrees, t s is not proportional to 1/((H/H s ) - 1). Higher frequency than 1 GHz may be hard to be applied in perpendicular recording if the angle between the head field and the direction perpendicular to the film plane is smaller than a few degrees.

Effect of Interface Structure on Exchange Biased Heusler Alloy Films

We report on the effects of grain size in antiferromagnetic IrMn layers exchange bias to Co2FeSi. We also report on an enhanced effect where Mn layers are inserted in the interface. The exchange-biased IrMn/Co2FeSi samples were grown by a HiTUS system, which allows us to control the grain size. The smaller IrMn grains were too small to give a large Hex while an Mn layer 0.5 nm thick dramatically increased Hex. This significant increase is attributed to optimization of the Mn concentration at the interface. This grain-size and interface tuning offers a way to control the exchange bias in such systems.

Switching time of single magnetic particle and maximum recording frequency of perpendicular magnetic recording

We investigated the switching time of a magnetic particle-which may impose limits on magnetic recording frequency-by computer simulation. We found that the difference in switching time between low and high temperatures decreases with increasing the angle /spl xi/ between the applied field and the easy direction, and scarcely changes with temperature if the angle is larger than a few degrees. This can be explained by considering the energy contour and locus of magnetization in switching. The switching times derived by using divided models, in which the particle is divided into 2/spl times/2/spl times/2 or 4/spl times/4/spl times/4 cells, are smaller than those derived by using an undivided model. But the difference between the switching times derived with the divided and undivided models is less than 1% if the angle /spl xi/ is larger than 1/spl deg/. We derived equations to express the switching times of the particle for the divided models at /spl xi/=0, and we used the equations to estimate the maximum recording frequency in perpendicular recording.

Effect of grain size on cluster size

A cluster size of a perpendicular medium was calculated from the correlation between grains in M‐H loops. The cluster size was affected by physical properties as follows. When grain size is small and exchange stiffness constant A is not zero, the cluster size increases with decreasing grain-size. The increment of the cluster size decreases with increasing grain size distribution. The cluster size divided by the average grain size (normalized cluster size) increases with an increasing intergranular exchange coupling constant he. The normalized cluster size can be estimated from the grain-size distribution and the intergranular exchange coupling constant.

Computer simulations of magnetization switching of elongated magnetic particles with shape defects

The switching fields of elongated magnetic particles with various shape defects were investigated by means of computer simulations. The magnetic particles were approximated by rectangular parallelepipeds that have groove or chip defects. We modeled 13 types of particle shape defects for two particle sizes. The particle sizes used were “small particle” 10 nm×10 nm×50 nm and “large particle” 40 nm×40 nm×200 nm. The magnetocrystalline anisotropy field in the magnetic particles was set to zero. The switching fields of the small and large particles were found to decrease with the number of groove defects, but they were independent of the total number of chip defects. The magnetic moments of all of the small particles rotated almost coherently. The switching fields of the small particles almost coincided with the average of the difference between the demagnetizing fields in all cells along two directions: An easy-axis direction and one of the hard-axis directions. That is, we obtained the switching fields with ...

Formation of Magnetic Clusters in Perpendicular Thin Films

The formation and growing process of magnetic clusters in perpendicular thin films were investigated using micromagnetic simulation. Two estimation methods of cluster size were proposed. CS(area) was defined as the diameter of the circle which has the same area as the reversed region. CS(corr) was defined from the correlation between magnetizations of adjacent grains. These cluster sizes were calculated in the demagnetizing process. The shape of the cluster can be estimated from comparison between CS(area) and CS(corr). If CS(area) is larger than CS(corr), string shape clusters are formed. If CS(area) coincides with CS(corr), there are nonstring shape clusters. In order to make cluster size small in the demagnetizing process it is useful for the perpendicular thin film to have grain size dispersion

Switching field and mechanism of cubic and flat square particles

Switching fields and mechanisms of cubic and flat square particles were investigated using computer simulation. The switching fields can be estimated from the nucleation fields obtained from the analytical equation for the coherent rotation or the curling modes of a sphere with the same diameter as the cubic particle or of an oblate spheroid with the same length of the principal axes as the flat square particle. When the magnetic moments rotate coherently in the initial stage (Mzav/Ms∼0.9, Mzav is the average magnetization in the easy direction and Ms is the saturation magnetization), the nucleation field of the coherent rotation mode accounts for the switching field. The switching fields of the flat square particle with chips were also investigated when the exchange stiffness constant was not small (=1.0×10−6 erg/cm). It was found that the chips increase the switching field and that the sum of the anisotropy field and the field due to shape anisotropy calculated from the average demagnetizing fields in t...

Magnetic Cluster Formation in Perpendicular Thin Films

In this study, we investigated the magnetic cluster formation in perpendicular thin films in demagnetizing process using micromagnetic simulation.

Influence of in-plane field on the thermal stability of perpendicular media

In order to investigate the effect of single pole type head scanning on output signal stability of perpendicular media, 2kOe static magnetic field was applied to the media. The results are as follows. Coupling of the in-plane component of the magnetic field and thermal agitation decrease output signal. On the other hand, the perpendicular component of the magnetic field scarcely affects the stability of the output signal. Exchange interaction between grains in the recording layer increases the stability of the output signal. Easy axis distribution of the recording layer decreases the stability. Exchange interaction between recording layer and soft magnetic underlayer (SUL) scarcely affects the stability. Anisotropy field of SUL does not affect the stability.

Effect of exchange interaction on R/W properties of single layer perpendicular recording media

Summary form only given. It has been reported (by Uesaka et al. (1999) and Matsumoto et al. (2000)) that a suitable exchange interaction between grains increases the signal and decreases the noise of single layer perpendicular recording media. The effects of anisotropy field, easy axis distribution and recording density to increase SNR (signal to noise ratio) with increasing exchange interaction were investigated. The material parameters used for the calculation were as follows: H/sub k/=10, 7.5, 5 kOe, standard deviation of the easy axis distribution=1 and 10 degrees, height of the media=20 nm, grain size=10 nm and Ms=400 emu/cm/sup 3/.