Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2002-07-11
2004-03-02
Le, N. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C324S252000
Reexamination Certificate
active
06700368
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for analyzing characteristics of a magnetic transducer such as an electromagnetic field characteristics and an magnetization characteristics of a magnetic transducer such as an inductive magnetic recording head for example.
DESCRIPTION OF THE RELATED ART
With the recent widespread use of personal computers, networked information is rapidly increasing. Such information includes not only conventional numerical data but also, for example, image data, and the volume of the information is increasing dramatically. Handling such an enormous amount of information requires a high-speed MPU as well as a high-speed, large-capacity, and high-reliability hard disk system.
When information is recorded magnetically on a recording medium such as a hard disk, a magnetic head having a coil wound around a soft magnetic material is used. With a so-called longitudinal recording medium that has an easy axis of magnetization in an in-plane direction, recording is achieved by the use of a leakage magnetic flux from a minute gap between two magnetic poles of a magnetic head made of a soft magnetic material. For this reason, the recording performance of a magnetic recording medium depends greatly not only on the characteristics of the medium but also on various factors that influence the recording magnetic field.
The factors that influence the recording magnetic field include primarily a film for protecting a magnetic medium and a head, a thickness of lubricant layer, a recess of a head magnetic pole, a magnetic spacing between the head and the medium that is determined by a floating height of the head, a length of a gap, magnetic poles, a magnetomotive force of a coil, and ICs and electrical circuits of a recording driver. Among these factors, a shape, magnetic characteristics, and magnetization structure of the head magnetic poles are important parameters in designing a magnetic head.
Conventionally, the design of a magnetic head often uses analysis based on a computer simulation. Computer-based analysis is used for performing an accurate, quick and quantitative analysis. This type of computer simulation has been a predominant tool in designing a magnetic head (Journal of Japanese Applied Magnetism Institute, Vol. 25, No. 3-1, pp.133-148, 2001).
In the design of a magnetoresistive effect (MR) read head, magnetic analysis is performed by using a micro-magnetic simulation (IEEE Trans Magn., Vol. 34, No. 4, p1516, 1998). For anisotropic magnetoresistive effect (AMR) heads, this method divides only an MR film and its soft adjacent layer (SAL) into elements, and for spin valve MR heads, only free layer and pin layer into elements. Then, based on an effective magnetic field that is the sum of a static magnetic field, an anisotropic magnetic field, an exchange magnetic field, and an external magnetic field, the Landau-Lifshitz-Gilbert (LLG) equation is solved for the magnetization in the elements (Jpn. J. Appl. Phys., 28, p2485, 1989). In this method, the static magnetic field calculation of which is the most time-consuming is determined by an integral equation method (IEM).
For the analysis of a magnetic recording head, only electromagnetic field analysis is performed by using finite element method (FEM), finite difference time domain method (FDTD method), integral equation method (IEM), or boundary element method, but no magnetization analysis is executed because a time required for this calculation is too long to complete analysis.
For an MR read head, only a very thin film is discreted, which has a pattern size of about 1 &mgr;m
2
and a thickness of no more than 0.1 &mgr;m. Therefore, the calculation of a static magnetic field requires only a small-scale calculation that involves elements of an order of 1000, so that a time required for calculating the static magnetic field is very short. In contrast to this, for a magnetic recording head, magnetic poles of a complex shape with a pattern size of several tens &mgr;m
2
and a thickness of the order of micro meters are divided into elements, so that the number of the elements is enormous ranging from several tens thousand to several hundreds thousand. Moreover, in order to consider eddy current effect, the depth of skin of a magnetic body should be expressed. Thus, it is inevitable that the region is divided into even smaller elements, and therefore the calculation of static magnetic field requires a longer time for each cycle of calculation for the magnetic recording head.
When the magnetization M in a steady state is calculated, the magnetization M is required to be calculated one by one self consistently and the static magnetic field needs to be calculated every time the magnetization M is updated. When the static magnetic field is calculated by the IEM that is used in the micromagnetic simulation, the time required for calculating the static magnetic field is proportional to N
3
, N being the number of elements. Thus, repetitively effecting the IEM calculation every time the magnetization is updated takes an enormous time for one-time calculation of magnetization unless each cycle of the calculation of the static magnetic field is short. Thus, for a magnetic recording head, the time required for calculation is so long that even a today's super computer is not enough. For this reason, magnetization analysis that requires multiple calculations of static magnetic field is not carried out. Thus, for the magnetic recording head, only an electromagnetic field analysis that requires a smaller number of magnetic field calculations is performed.
However, the shape of magnetic poles and magnetic characteristics such as anisotropy and magnetostriction of the magnetic poles determine magnetization structure, and influence the ability of the magnetic recording head seriously, so that analysis in terms of magnetization has been desired in analyzing a magnetic recording head.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method and a program for analyzing characteristics that are capable of analyzing the magnetization of a magnetic transducer such as a magnetic recording head.
According to the present invention, a method for analyzing characteristics of a magnetic transducer includes a step of sub-dividing a region to be analyzed, in a magnetic transducer into a plurality of polyhedral elements, based on at least data representing a shape of the region in the magnetic transducer, and a step of performing a transient calculation. The transient calculation includes calculating a transient electric field of each of the plurality of polyhedral elements by using a conductivity and a dielectric constant of each of the plurality of polyhedral elements, a transient electric field of each of the plurality of polyhedral elements, calculated at one preceding time step (&Dgr;t), a transient magnetic field of each of the plurality of polyhedral elements, calculated at ½ preceding time step (&Dgr;t/2), and a current density of each of the plurality of polyhedral elements, calculated at ½ preceding time step (&Dgr;t/2), calculating a transient magnetic field of each of the plurality of polyhedral elements by using a transient magnetic field of each of the plurality of polyhedral elements, calculated at one preceding time step (&Dgr;t), a transient electric field of each of the plurality of polyhedral elements, calculated at ½ preceding time step (&Dgr;t/2), and a magnetic permeability of each of the plurality of polyhedral elements, and updating the magnetic permeability in accordance with a magnetic flux density determined from the calculated transient magnetic field. The step of performing transient calculation is repeated until a predetermined number of time steps have been completed, to determine electric fields and magnetic fields of all of the plurality of polyhedral elements in the region to be analyzed.
For each of polyhedral elements, a transient electric field and a magnetic field are calculated one alternately with the other by shifting ½
Armstrong Kratz Quintos Hanson & Brooks, LLP
Aurora Reena
Le N.
TDK Corporation
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