1. Field of the Invention
The present invention relates to a thin-film magnetic head for reading and writing signals by means of a perpendicular magnetic recording, a head gimbal assembly (HGA) with the thin-film magnetic head and a magnetic disk drive apparatus with the HGA, and to a manufacturing method of the thin-film magnetic head for the perpendicular magnetic recording.
2. Description of the Related Art
In recent years, the perpendicular magnetic recording has been actively developed instead of conventional longitudinal magnetic recording to realize more improvement in areal recording density of the magnetic disk drive apparatus.
In the perpendicular magnetic recording, a demagnetization field drastically decreases in a magnetization transition region, and therefore, the magnetization transition width can become much smaller than that of the longitudinal magnetic recording. Furthermore, the perpendicularly recorded magnetization is not greatly affected by a thermal fluctuation that becomes serious problem in the longitudinal magnetic recording with higher recording density. Therefore, it becomes possible to obtain stable higher-density recording in the perpendicular magnetic recording.
A thin-film magnetic head for the perpendicular magnetic recording has been proposed, which has a single pole structure including a main magnetic pole, an auxiliary magnetic pole as a return yoke, and an inductive coil inducing a magnetic flux in these magnetic poles. Generally, the magnetic head also has magnetic shields provided in the leading and/or trailing sides of the main magnetic pole. As the same time, a magnetic disk has been proposed which has a multilayer structure of a soft-magnetic backing layer acting as a part of a magnetic circuit and a perpendicular magnetic recording layer.
In the thin-film magnetic head, a field generated from the main magnetic pole performs writing to the magnetic disk. FIG. 1 shows a schematic drawing illustrating a simulated distribution of a magnetic field generated from the conventional main magnetic pole, and recorded bits. In the figure, only the magnetic field generated from the main magnetic pole 10 is illustrated. The cross-section of the main magnetic pole 10 has a trapezoid shape due to the formation of bevel angles against a skew angle arising from an arm driving by means of a rotary actuator, which possibly causes unnecessary signals to be recorded on adjacent tracks. Broken lines show magnetic field contour lines.
As shown in FIG. 1, the contours of the magnetic field generated from the main magnetic pole 10 has a curvature in such a way as to surround the main magnetic pole 10 itself. Recorded bits 11 are formed on the magnetic disk along the contour line that lies in the trailing side, that is, in the downstream side of the disk rotation, and is equivalent to a coercive force of the magnetic disk. As a result, the shape of the magnetization transition region 12 as a boundary region between recorded bits 11 also has a curvature. Therefore, when a magnetoresistive (MR) read head element reads signal fields generated from the recorded bits 11 with the curved transition regions 12, a jitter becomes larger due to the increase in a reverse width of a reproduction power, and the larger jitter causes an error rate to be increased. Moreover, the length of the recorded bit 11 can not be shorten down to the curvature width WTC of the transition region 12, which hinders higher recording density.
As a technique improving the magnetization transition region, for example, a structure that an opposed portion of the auxiliary magnetic pole to the main magnetic pole is protruded in order to suppress the broadening of a magnetic field distribution at track edges, is described in Japanese Patent Publication No. 2002-092820A, in which no curvature of the magnetic field is mentioned. Further, in U.S. patent application Ser. No. 10/880,509, it is described that the main magnetic pole has a double-layered structure of the first layer formed of, for example, CoFe and the second layer formed of, for example, NiFe, CoNiFe or CoFe, though not to improve the magnetization transition region. Furthermore, a structure of the main magnetic pole that has a concave portion in the trailing side of an air bearing surface (ABS) in order to reduce the degree of the curvature of the transition region, is described in U.S. Pat. No. 6,741,421.
However, the structure with the protrusion described in Japanese Patent Publication No. 2002-092820A is not adequate to control the degree of the curvature. The structure is just for suppressing the broadening of the magnetic field distribution and concentrating the magnetic field, and can not positively control the curvature. Further, the double-layered structure described in U.S. patent application Ser. No. 10/880,509 has no purpose of improving the transition region. Actually, there is no specification about the thickness of each layer in the description, and mere double-layered structure itself can not realize the desired degree of the curvature.
Furthermore, the structure with the concave portion described in U.S. Pat. No. 6,741,421 has a difficulty in forming the concave portion with high accuracy. In other words, the size and depth of the concave portion can not be precisely controlled because the concave portion is formed by digging the magnetic material layer with ion-milling method and so on. However, the degree of the curvature of the magnetic contour, which determines the shape of the magnetization transition region, is sensitive to the shape of the concave portion. Therefore, the contour with small curvature can not be obtained stably.
Furthermore, because a non-magnetic material is embedded in the concave portion, an adequate write field is difficult to be obtained near the trailing edge of the main magnetic pole, which is a main portion for writing, compared to the case without the concave portion.
Moreover, in an MR read head element utilizing giant magnetoresistive (GMR) effect or tunnel magnetoresistive (TMR) effect, a pinned layer, a separation layer and a free layer, which are main components, are usually stacked sequentially on a hard-bias layer. Therefore, in some cases, the free layer that receives signal fields has a curvature with a reverse direction to that of the curvature of the transition region. On this case, a magnetic sensitivity contour that expresses a sensitivity level to a magnetic field of the MR read head element also has a curvature with the reverse direction to that of the curvature of the transition region. As a result, a jitter becomes larger due to the increase in the reverse width of the reproduction power, and the larger jitter causes the error rate to be increased.
Therefore, only reducing the degree of the curvature of the magnetic field contour is not sufficient, and it is needed to design the magnetic field contour with wide design range including the direction of the curvature in consideration of the magnetic sensitivity contour of the MR read head element. Without such a design, the error rate can not be sufficiently decreased by reducing the reverse width of the reproduction power.