JP2012234597A - Inspection method and manufacturing method for magnetic recording medium, and magnetic recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection method for a magnetic recording medium improving inspection accuracy on the magnetic recording medium.SOLUTION: The inspection method for inspecting a surface of a magnetic recording medium M having a magnetic layer on at least a non-magnetic substrate comprises the steps of: extracting a first signal outputted from a heat sensitive element at a portion specified as a defect portion, out of signals outputted from heat sensitive elements while scanning with an inspection head 22 including the heat sensitive elements at a first height on the surface of the magnetic recording medium M to be an inspection object; extracting a second signal outputted from the heat sensitive element at the specified portion while subsequently scanning with the inspection head 22 at a second height different from the first height; and comparing the first signal and the second signal with each other to discriminate whether or not the defect portion has a concave shape or a convex shape on the surface of the magnetic recording medium M.

Description

  The present invention relates to a method for inspecting and manufacturing a magnetic recording medium, and a magnetic recording / reproducing apparatus.

  2. Description of the Related Art A magnetic recording / reproducing apparatus represented by a hard disk drive (HDD) is widely used as an external storage device for an information processing apparatus such as a computer, and has recently been used as a moving picture recording apparatus.

  The HDD has a disk-shaped (doughnut-shaped) magnetic recording medium having an opening in the center, a single or a plurality of these stacked and rotated concentrically (in the case of multiple disks, a synchronous rotation), a shaft A magnetic recording medium rotatably supported via a bearing on a magnetic recording medium, a magnetic head for recording and / or reproducing on both sides of the magnetic recording medium, a support arm to which the magnetic head is attached, and a support arm A plurality of stacks are stacked (this is called a head stack assembly) and moved in the radial direction synchronously to move the magnetic head to an arbitrary position on the magnetic recording medium, and the head stack mechanism is driven. Voice coil motor (VCM) and a signal processing system for processing signals from the magnetic head and signals to the magnetic head and VCM It is.

  In the HDD, a magnetic recording medium incorporated in the HDD is rotated at a high speed of several thousand rpm or more by a motor, and a head slider on which the magnetic head is mounted is slightly levitated by an air flow flowing over the magnetic recording medium. A servo signal (position information signal or the like) is magnetically written on the magnetic recording medium, and this signal is detected by the magnetic head, and the position of the magnetic head on the magnetic recording medium is determined based on this signal, A magnetic head reads and writes magnetic information at a specific position on the magnetic recording medium.

  A magnetic recording medium mounted on an HDD is generally produced by sequentially forming an underlayer, a magnetic layer, a protective layer, a lubricating layer, and the like on the surface of a substrate made of an aluminum alloy, a glass substrate, or the like. Then, as an evaluation process for the manufactured magnetic recording medium, a glide inspection and a certification inspection are performed.

  The glide inspection is a process for inspecting the presence or absence of protrusions on the surface of the magnetic recording medium. That is, when a magnetic recording medium is recorded and reproduced using a magnetic head, if there is a protrusion on the surface of the magnetic recording medium that is higher than the flying height (the distance between the medium and the magnetic head), the magnetic head becomes a protrusion. The collision may cause damage to the magnetic head or cause a defect in the magnetic recording medium. Therefore, in this step, the surface of the magnetic recording medium is inspected for such high protrusions, and the magnetic recording medium having such protrusions is excluded from the manufacturing process as a defective product (for example, Patent Document 1). reference).

  For magnetic recording media that have passed the glide test, a certification test is performed. The certify test is the same as recording and reproduction in a normal HDD on a magnetic recording medium. After recording a predetermined signal using a magnetic head, the signal is reproduced and magnetic recording is performed from the obtained reproduction signal. This is a process for confirming the defect or quality of the electromagnetic conversion characteristics of the medium (see, for example, Patent Document 2). And about the magnetic recording medium which passed the certification | certification test | inspection, after writing servo information etc. using the apparatus called a servo writer, it will be mounted in HDD.

  By the way, in the HDD, as the recording density of a magnetic recording medium increases, an MR element using a magnetoresistive (MR) effect or a GMR using a giant magnetoresistive (GMR) effect as an element for reading a magnetic signal during reproduction. 2. Description of the Related Art A magnetic head including an element, a TuMR element using a tunnel magnetoresistance (TuMR) effect, and the like is used. However, in an HDD using such a reading element, frictional heat is generated when the reading element collides with a protrusion on the surface of the magnetic recording medium during reproduction of the magnetic recording medium, resulting in an increase in temperature of the reading element. The phenomenon that the magnetic signal to be reproduced fluctuates due to the fluctuation of the resistance value, that is, the occurrence of the thermal asperity phenomenon is a problem.

  In general, the thermal asperity phenomenon means that when a reading element provided on a magnetic head and a protrusion on the surface of a magnetic recording medium come into contact with each other, a sudden temperature rise occurs in the reading element due to the contact heat. This is a phenomenon in which the electric resistance value of the reading element fluctuates.

  This thermal asperity phenomenon becomes more conspicuous due to a decrease in the flying height of the magnetic head accompanying an increase in recording density of the magnetic recording medium. In addition, the magnetic head collides with minute projections, which are defects inevitably present on the surface of the magnetic recording medium, which accelerates the wear of the magnetic head and causes head deterioration failures such as output reduction and characteristic deterioration. Yes.

  Since the size of the defect causing these problems is very small, it is necessary to increase the inspection accuracy during the manufacture of the magnetic recording medium. Therefore, a method for evaluating the surface characteristics of a magnetic recording medium using a signal resulting from a thermal asperity phenomenon caused by contact between a test head having a thermal element (MR element) and a protrusion generated on the surface of the magnetic recording medium. Has been proposed (see, for example, Patent Document 3).

  In addition, the surface of the magnetic recording medium is scanned using a thermal element (MR element), and the signal caused by the long period waviness of 40 μm or more on the surface of the magnetic recording medium is separated from the signal output from the thermal element. In addition, a method for detecting a protrusion on the surface of the magnetic recording medium from the separated signal has been proposed (see, for example, Patent Document 4).

JP 11-260014 A JP 2003-257016 A JP-A-10-105908 JP 2008-146803 A

  As described above, when there is an abnormal protrusion on the surface of the magnetic recording medium, the abnormal protrusion and the inspection head collide to generate a thermal asperity phenomenon. Therefore, by detecting a signal caused by this thermal asperity phenomenon, The presence or absence of protrusions on the surface of the magnetic recording medium can be determined.

  However, in the conventional inspection method, as disclosed in the above-mentioned Patent Document 4, not only a protrusion-shaped defect but also a long-period swell including a recessed shape is detected. Therefore, a protrusion defect that causes a thermal asperity phenomenon is detected. There was a problem that it could not be identified accurately.

  For this reason, in the actual certification inspection, even when an output signal is generated due to the defect including the above-described dent shape, the magnetic recording medium is judged as a defective product, which leads to a significant decrease in product yield.

  The present invention has been proposed in view of such conventional circumstances, and a magnetic recording medium inspection method with improved inspection accuracy with respect to the magnetic recording medium, as well as the product yield by using this inspection method. Provided are a method of manufacturing a magnetic recording medium that can be further improved, and a magnetic recording / reproducing apparatus that can be further improved in reliability by including a magnetic recording medium manufactured by using this manufacturing method. For the purpose.

The present invention provides the following means.
(1) A magnetic recording medium inspection method for inspecting a surface of a magnetic recording medium having a magnetic layer on at least a nonmagnetic substrate,
On the surface of the magnetic recording medium to be inspected, the thermal element at a location specified as a defective portion in the signal output from the thermal element while scanning the inspection head having the thermal element at the first height. Extracting a first signal output from
Then, extracting the second signal output from the thermal element at the specified location while scanning the inspection head at a second height different from the first height;
And comparing the first signal with the second signal to determine whether the defective portion has a concave shape or a convex shape on the surface of the magnetic recording medium. Inspection method for recording media.
(2) When the change of the second signal with respect to the first signal when the second height is changed with respect to the first height has regularity, the defect portion is While determining that the surface of the magnetic recording medium has a concave shape, and having irregularity, it is determined that the defective portion has a convex shape on the surface of the magnetic recording medium (1) ) Inspection method for magnetic recording media.
(3) The method for inspecting a magnetic recording medium according to (1) or (2), wherein the inspection head is scanned over the inner and outer circumferences of the magnetic recording medium while rotating the magnetic recording medium. .
(4) The magnetic recording medium inspection method according to any one of (1) to (3), wherein a magnetoresistive element is used as the thermal element.
(5) A method of manufacturing a magnetic recording medium having a magnetic layer on at least a nonmagnetic substrate,
A method of manufacturing a magnetic recording medium, comprising a step of inspecting the surface of the magnetic recording medium using the inspection method according to any one of (1) to (4).
(6) A magnetic recording / reproducing apparatus comprising: a magnetic recording medium manufactured using the manufacturing method according to item (5); and a magnetic head for recording / reproducing information with respect to the magnetic recording medium.

  As described above, according to the present invention, it is possible to determine whether the defective portion on the surface of the magnetic recording medium has a concave shape or a convex shape, and thus a convex shape that causes thermal asperity phenomenon or wear of the magnetic head. It is possible to greatly improve the accuracy of detection of defects (projections).

  According to the present invention, by using this inspection method, a magnetic recording medium manufacturing method capable of further improving the product yield, and a magnetic recording medium manufactured using this manufacturing method are provided. Thus, it is possible to provide a magnetic recording / reproducing apparatus capable of further improving the reliability.

It is sectional drawing which shows an example of the magnetic recording medium used as the test object of this invention. It is a perspective view which shows an example of the test | inspection apparatus used in the test | inspection method of the magnetic recording medium to which this invention is applied. (A) is an AFM image showing a convex defect, and (b) is a waveform diagram of a signal output from the thermal element due to the convex defect. (A) is an AFM image showing a concave defect, and (b) is a waveform diagram of a signal output from the thermal element due to the concave defect. It is a graph which shows the result of having measured the electric potential (signal intensity | strength) output from a thermal element when a test | inspection head scans on a concave-shaped defect. It is a graph which shows the result of having measured the electric potential (signal intensity | strength) output from a thermosensitive element when a test | inspection head scans on a convex-shaped defect. It is a perspective view which shows an example of a magnetic recording / reproducing apparatus.

Hereinafter, a magnetic recording medium inspection method and manufacturing method to which the present invention is applied, and a magnetic recording / reproducing apparatus will be described in detail with reference to the drawings.
In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent. The dimensions and the like exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto, and can be appropriately modified and implemented without departing from the scope of the invention.

  As a result of earnest studies on the above problems, the present inventor has been caused by contact between the thermal element (MR head) of the above-described inspection head and protrusions (convex defects) on the surface of the magnetic recording medium. In addition to the thermal asperity phenomenon that occurs, in addition to long-period undulations with a wavelength of 40 μm or more formed on the surface of a magnetic recording medium (with a concave defect width of 20 μm or more), a concave defect with a width of about 10 μm or less Also found that the thermal asperity phenomenon occurs.

  In this case, the thermal asperity phenomenon occurs without contact between the inspection head and the surface of the magnetic recording medium. In addition, the signal output from the thermal element due to the concave defect having a width of about 10 μm or less is very similar to the signal output from the thermal element due to the convex defect having the same size as the conventional magnetic field. It is difficult to distinguish both by the inspection method of the recording medium. Therefore, in the conventional magnetic recording medium inspection method, a magnetic recording medium having a concave defect is erroneously determined as a magnetic recording medium having a convex defect. Moreover, the probability of such erroneous determination increases as the signal output from the thermal element becomes weaker.

  Therefore, the present inventor has determined that the signal output from the thermosensitive element is caused by a convex defect having a width of about 10 μm or less on the surface of the magnetic recording medium, or by a concave defect having the same size. Further examination was conducted on a method for determining whether or not. As a result, when the height of the inspection head (distance from the magnetic recording medium) is changed while scanning the inspection head having the thermal element on the surface of the magnetic recording medium to be inspected, the concave shape It is found that there is a difference between the change in the signal output from the thermal element due to the defect and the change in the signal output from the thermal element due to the convex defect, and this difference causes the defect on the surface of the magnetic recording medium to be convex or The inventors have found that it is possible to determine whether a concave shape is present, and have completed the present invention.

  That is, the present invention relates to a magnetic recording medium inspection method for inspecting the surface of a magnetic recording medium having a magnetic layer on at least a nonmagnetic substrate, wherein a thermal element is provided on the surface of the magnetic recording medium to be inspected. A step of extracting a first signal output from a thermal element at a location specified as a defective portion from signals output from the thermal element while scanning an inspection head having a first height; Extracting the second signal output from the thermal element at the specified location while scanning the inspection head at a second height different from the first height; and the first signal and the second signal; And determining whether the defective portion has a concave shape or a convex shape on the surface of the magnetic recording medium.

(Magnetic recording medium)
Specifically, FIG. 1 is a cross-sectional view showing an example of a magnetic recording medium to be inspected using a magnetic recording medium inspection method to which the present invention is applied.
The magnetic recording medium to be inspected has a nonmagnetic underlayer 2, a magnetic layer 3, a protective layer 4, and a liquid lubricating layer 5 on both main surfaces of a disk-shaped nonmagnetic substrate 1 having a center hole. It consists of the thing laminated | stacked one by one. As a magnetic recording medium to be inspected, in addition to the double-sided type shown in FIG. 1, a nonmagnetic underlayer 2, a magnetic layer 3, and a protective layer 4 are formed on one main surface of the nonmagnetic substrate 1. Alternatively, a single-sided type in which the liquid lubricating layer 5 is sequentially laminated may be used. Further, the magnetic recording medium to be inspected may be an in-plane magnetic recording medium or a perpendicular magnetic recording medium. That is, the magnetic recording medium inspection method to which the present invention is applied can be widely applied to at least a magnetic recording medium having a magnetic layer on a nonmagnetic substrate. Etc. can be implemented with appropriate changes.

(Inspection equipment)
FIG. 2 is a perspective view showing an example of an inspection apparatus used in a magnetic recording medium inspection method to which the present invention is applied.
In this inspection apparatus, a spindle motor 21 that rotates a magnetic recording medium M to be inspected at a predetermined rotation number, an inspection head 22 that inspects the surface of the magnetic recording medium M, and an inspection head 22 are attached to the tip. The support arm 23, the voice coil motor 24 that positions the inspection head 22 on the surface of the magnetic recording medium M while moving the support arm 23 in the radial direction of the magnetic recording medium M, and the inspection head 22 includes the magnetic recording medium M. And a signal processing circuit 25 for performing signal processing for inspecting the surface of the substrate.

  In this evaluation apparatus, it is possible to inspect three magnetic recording media M at the same time, and the three magnetic recording media M are synchronously rotated about a coaxial center by a spindle motor 21. The evaluation apparatus also includes a head stack assembly 23A configured such that a plurality of support arms 23 rotate coaxially about a pivot 23a. The head stack assembly 23 </ b> A is driven by a voice coil motor 24, and the driving of the voice coil motor 24 is controlled by a signal processing circuit 25.

  The inspection head 22 attached to the distal end portion of each support arm 23 is provided with a thermal element (not shown) whose physical property value such as a resistance value changes as the temperature rises. Examples of the thermosensitive element include an MR element using a magnetoresistive (MR) effect, a GMR element using a giant magnetoresistive (GMR) effect, a TMR element using a tunnel magnetoresistive (TuMR) effect, etc. (hereinafter collectively) A magnetoresistive element).

  Further, the inspection head 22 can adjust the height of the thermal element with respect to the surface of the magnetic recording medium by changing the number of rotations (movement speed) of the magnetic recording medium. Alternatively, the height can be adjusted by expanding or contracting the vicinity of the thermal element by the heat generated by the heater disposed near the thermal element.

  The signal processing circuit 25 is electrically connected to each inspection head 22 by a flexible printed circuit board 26, and each inspection head 22 can be individually controlled by this signal processing circuit 25.

  Further, the inspection apparatus is provided with a retreat area 27 for retreating the inspection head 22 attached to the tip of each support arm 23 when the magnetic recording medium M is replaced. Since the retreat area 27 is slightly buffered with the magnetic recording medium M, when replacing the magnetic recording medium M, the retreat area 27 is moved together with the inspection heads 22 and retreated with the magnetic recording medium M. It is necessary to separate the area.

  When performing a certification inspection for inspecting the surface of the magnetic recording medium M using the inspection apparatus having the above-described structure, the magnetic recording medium M is rotated at a predetermined rotational speed by the spindle motor 21 and a voice coil motor. While the head stack assembly 23A is controlled to rotate about the pivot 23a by 24, the inspection head 22 attached to the tip of each support arm 23 is scanned over the inner and outer circumferences on the surface of the magnetic recording medium M. Then, a defect portion on the surface of the magnetic recording medium M is identified from the signal output from the thermal element of the inspection head 22, and the signal output from the thermal element at the identified location is the surface of the magnetic recording medium M. The magnetic recording medium inspection method to which the present invention is applied is discriminated whether it is due to a convex defect or a concave defect.

  In the above inspection apparatus, a case where a plurality of (three in this example) magnetic recording media M are inspected simultaneously has been described as an example. However, the magnetic recording media M can be inspected one by one. It is.

(Inspection method for magnetic recording media)
In the method of inspecting a magnetic recording medium to which the present invention is applied, first, on the surface of the magnetic recording medium M to be inspected, the inspection head 22 having a thermal element is moved to a first height (from the surface of the magnetic recording medium to the thermal element). The first signal output from the thermal element at the location identified as the defective portion is extracted from the signals output from the thermal element while scanning at the first height).

  Here, FIG. 3A shows an AFM image of a convex defect (width 0.6 μm, height 34 nm) on the surface of the magnetic recording medium, and the signal output from the thermal element due to the convex defect is shown in FIG. A waveform diagram is shown in FIG.

  The signal output from the thermal element shown in FIG. 3B is due to the thermal asperity phenomenon when the thermal element contacts the convex defect on the surface of the magnetic recording medium shown in FIG. is there.

  On the other hand, an AFM image of a concave defect (width 2.9 μm, depth 94 nm) on the surface of the magnetic recording medium is shown in FIG. 4A, and is output from the thermal element due to the concave defect. A signal waveform diagram is shown in FIG.

  The output signal from the thermosensitive element shown in FIG. 4B is due to heat dissipation of the thermosensitive element through the air layer between the magnetic recording medium M and the inspection head 22, and such a signal is generated from the magnetic recording medium M. It becomes easier to occur as the distance between the surface and the inspection head 22 becomes smaller.

  That is, conventionally, since there is no collision between the concave defect on the surface of the magnetic recording medium and the thermal element, the temperature of the thermal element due to contact heat and the change in the signal output caused by this cannot occur. It was thought. As a result of investigation by the present inventor, since a current for detecting a resistance change is supplied to the thermosensitive element, the thermosensitive element itself generates heat and its temperature is higher than that of the magnetic recording medium. The heat from the thermosensitive element is radiated to the magnetic recording medium through the air layer between the magnetic recording medium M and the inspection head 22. At this time, in the case of a concave defect on the surface of the magnetic recording medium M, the distance between the surface of the magnetic recording medium M and the thermal element is increased. Therefore, even if the size of the defect is as small as about 10 μm or less. The heat dissipation is hindered. As a result, it was found that the temperature of the thermal element instantaneously increased, which caused the thermal asperity phenomenon of the thermal element, and as a result, a signal as shown in FIG. 4B was output.

  Next, while scanning the inspection head 22 at a second height different from the first height (second height from the surface of the magnetic recording medium to the thermal element), the output from the thermal element at the specified location is output. The second signal to be extracted is extracted.

  Here, the AFM is used to determine the width and height of the concave defect (concave 1 to 10) and the convex defect (convex 1 to 10) on the surface of the magnetic recording medium M. Table 1 summarizes the measurement results.

  Further, while changing the distance (height) [nm] of the inspection head 22 with respect to the surface of the magnetic recording medium M every 1 nm within a range of 1 to 12 nm, the concave defects (concave 1 to concave 10 shown in Table 1). FIG. 5 shows the result of measuring the potential (signal intensity) [mV] output from the thermosensitive element when the inspection head 22 scans the top. Similarly, the result of measuring the potential (signal intensity) [mV] of the signal output from the thermal element when the inspection head 22 scans the convex defect (convex 1 to convex 10) shown in Table 1. Is shown in FIG. The surface of the magnetic recording medium is based on the case where the surface is smooth (when there are no concave and convex defects).

  Next, it is determined whether the defective portion has a concave shape or a convex shape on the surface of the magnetic recording medium M by comparing the first signal and the second signal. Specifically, when the change of the second signal with respect to the first signal when the second height is changed with respect to the first height has regularity, the defective portion is a magnetic recording medium. On the other hand, it is determined that the surface of the magnetic recording medium has a concave shape. On the other hand, if it has irregularity, it is determined that the defective portion has a convex shape on the surface of the magnetic recording medium.

  That is, as shown in the graph of FIG. 5, when a concave defect (concave 1 to concavity 10) exists on the surface of the magnetic recording medium M, any signal output from the thermal element is gently attenuated. It can be seen that a curve is drawn. This is because when the heat from the thermosensitive element is radiated to the magnetic recording medium M, the amount of radiated heat changes depending on the thickness of the air layer between the surface of the magnetic recording medium M and the inspection head 22, and the amount of change. Is considered to be uniform.

  On the other hand, as shown in the graph of FIG. 6, when there are convex defects (convex No. 1 to No. 10) on the surface of the magnetic recording medium M, the signals output from the thermal elements are all It can be seen that the curve is uneven. This is because the signal output from the thermal element is due to a collision between the thermal element and a convex defect, so that even if the distance (height) of the inspection head 22 to the surface of the magnetic recording medium M changes, the convex shape This is considered to be because a signal resulting from the thermal asperity phenomenon is output when the thermal element contacts the defect.

  Here, whether or not the change in the second signal with respect to the first signal has regularity is determined by whether or not the change in the signal described above becomes a gentle attenuation curve. In the case of performing the conversion, the change of the second signal with respect to the first signal is approximated to a curve by the least square method, and the difference between the approximated curve and the actually measured value can be converted into a numerical value.

  As described above, in the method for inspecting a magnetic recording medium to which the present invention is applied, since it is possible to determine whether a defective portion on the surface of the magnetic recording medium M has a concave shape or a convex shape, a thermal asperity phenomenon or a magnetic head It is possible to greatly improve the accuracy of detecting convex defects (projections) that cause wear of the surface.

(Method of manufacturing magnetic recording medium)
A method of manufacturing a magnetic recording medium to which the present invention is applied includes a step of inspecting the surface of the magnetic recording medium using the inspection method of the present invention.
That is, in the inspection process of the present invention, it is determined whether the defect portion on the surface of the magnetic recording medium M has a concave shape or a convex shape by using the magnetic recording medium inspection method to which the present invention is applied. be able to. When this defective portion is determined to be a convex defect, the magnetic recording medium is determined to be a rejected product.

  As a result, it is possible to improve the detection accuracy of convex defects (projections) that cause the above-described thermal asperity phenomenon and wear of the magnetic head, thereby further improving the product yield.

(Magnetic recording / reproducing device)
FIG. 7 is a perspective view showing an example of a magnetic recording / reproducing apparatus (HDD).
This magnetic recording / reproducing apparatus includes a magnetic recording medium 30 manufactured by using the manufacturing method of the present invention, and a rotation driving unit that rotates the magnetic recording medium (medium driving unit that drives the magnetic recording medium in the recording direction). 31, a magnetic head 32 that performs recording and reproducing operations on the magnetic recording medium 30, and a head drive unit that moves the magnetic head 32 in the radial direction of the magnetic recording medium 30 (moving the magnetic head relative to the magnetic recording medium) Head moving means) 33 and a recording / reproducing signal processing system (recording / reproducing signal processing means) 34 for inputting a signal to the magnetic head 32 and reproducing an output signal from the magnetic head 32.

  In this magnetic recording / reproducing apparatus, it is possible to further improve the reliability by using the magnetic recording medium 30 that has been determined to pass in the inspection process of the present invention.

  Hereinafter, the effects of the present invention will be made clearer by examples. In addition, this invention is not limited to a following example, In the range which does not change the summary, it can change suitably and can implement.

  In this example, a magnetic recording medium having an outer diameter of 2.5 inches similar to that shown in FIG. 1 is manufactured, and the surface of the magnetic recording medium is inspected using an inspection head having a thermal element. It was.

  Before performing this inspection, use a glide tester equipped with a head with a piezoelectric element to determine the glide height of the head (the distance between the head and the surface of the magnetic recording medium when there is no defect on the surface). A glide test was performed to exclude magnetic recording media having a large protrusion on the surface at 30 nm.

  Then, 100 magnetic recording media that passed the glide test were prepared, and a certification test using a test head having a thermal element was performed on each magnetic recording medium. Specifically, in this certification inspection, a glide height (height from the surface of the magnetic recording medium to the thermal element) is set to 4 nm, and a defective portion having a signal output from the thermal element of the inspection head of 500 mV or more is detected. And the signal output from a thermosensitive element was measured at each height, changing the glide height to 10 nm per 1 nm unit in this defect location.

  Thereafter, the signal output from the thermal element, that is, the signal output from the thermal element in a glide height range of 4 nm to 10 nm was approximated as an attenuation curve by the least square method. A case where the difference between the approximate attenuation curve and the actually measured value was 5% or less was determined as a concave defect, and a case where the difference was higher than 5% was determined as a convex defect.

  And when the defect location of the magnetic recording medium detected by this certification inspection was observed with AFM, 6 locations judged as concave defects and 5 locations judged as convex defects were all defective. The shape was consistent with the above judgment, and it was found that the certification inspection according to the present invention was accurate.

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic board | substrate 2 ... Nonmagnetic base layer 3 ... Magnetic layer 5 ... Protective layer 6 ... Liquid lubricating layer M ... Magnetic recording medium 21 ... Spindle motor 22 ... Inspection head, 23A ... Head stack assembly 23 ... Support arm 23a ... Pivot DESCRIPTION OF SYMBOLS 24 ... Voice coil motor 25 ... Signal processing circuit 30 ... Magnetic recording medium 31 ... Medium drive part 32 ... Magnetic head 33 ... Head drive part 34 ... Recording / reproduction signal processing system

Claims (6)

A method for inspecting a magnetic recording medium for inspecting a surface of a magnetic recording medium having a magnetic layer on at least a nonmagnetic substrate,
On the surface of the magnetic recording medium to be inspected, the thermal element at a location specified as a defective portion in the signal output from the thermal element while scanning the inspection head having the thermal element at the first height. Extracting a first signal output from
Then, extracting the second signal output from the thermal element at the specified location while scanning the inspection head at a second height different from the first height;
And comparing the first signal with the second signal to determine whether the defective portion has a concave shape or a convex shape on the surface of the magnetic recording medium. Inspection method for recording media.   When the change of the second signal with respect to the first signal when the second height is changed with respect to the first height has regularity, the defect portion becomes the magnetic recording. 2. The method according to claim 1, wherein, when the surface of the medium is determined to have a concave shape, the defect portion is determined to have a convex shape on the surface of the magnetic recording medium when the surface has irregularity. Inspection method for magnetic recording media.   3. The magnetic recording medium inspection method according to claim 1, wherein the inspection head is scanned over the inner and outer circumferences of the magnetic recording medium while rotating the magnetic recording medium.   The magnetic recording medium inspection method according to claim 1, wherein a magnetoresistive element is used as the thermal element. A method of manufacturing a magnetic recording medium having a magnetic layer on at least a nonmagnetic substrate,
A method for manufacturing a magnetic recording medium, comprising the step of inspecting the surface of the magnetic recording medium using the inspection method according to claim 1.   A magnetic recording / reproducing apparatus comprising: a magnetic recording medium manufactured by using the manufacturing method according to claim 5; and a magnetic head for recording / reproducing information with respect to the magnetic recording medium.

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