JPH04286701A - Magnetic recording and reproducing device - Google Patents
Magnetic recording and reproducing deviceInfo
- Publication number
- JPH04286701A JPH04286701A JP5252091A JP5252091A JPH04286701A JP H04286701 A JPH04286701 A JP H04286701A JP 5252091 A JP5252091 A JP 5252091A JP 5252091 A JP5252091 A JP 5252091A JP H04286701 A JPH04286701 A JP H04286701A
- Authority
- JP
- Japan
- Prior art keywords
- magnetic
- recording
- coil
- current
- circuit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000010409 thin film Substances 0.000 claims abstract description 18
- 239000010408 film Substances 0.000 claims abstract description 11
- 230000007704 transition Effects 0.000 claims 1
- 235000002017 Zea mays subsp mays Nutrition 0.000 abstract description 7
- 241000482268 Zea mays subsp. mays Species 0.000 abstract description 7
- 238000010586 diagram Methods 0.000 description 11
- 230000010355 oscillation Effects 0.000 description 4
- 230000001960 triggered effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000005389 magnetism Effects 0.000 description 1
- 230000005415 magnetization Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
Landscapes
- Digital Magnetic Recording (AREA)
Abstract
Description
【０００１】0001
【産業上の利用分野】本発明は磁気ディスク装置等の磁
気記録再生装置に関し、更に詳述すれば薄膜磁気ヘッド
を備えた磁気記録再生装置に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording and reproducing apparatus such as a magnetic disk drive, and more specifically to a magnetic recording and reproducing apparatus equipped with a thin film magnetic head.
【０００２】0002
【従来の技術】磁気ディスク装置における記録密度の向
上を目的として薄膜磁気ヘッド（以下薄膜ヘッドという
）が開発されている。これは基板上に磁極となる２層の
薄い磁性膜を相隔てて形成し、この間にコイルを配し、
２層の磁性膜の端部にギャップを形成してあるものであ
る。2. Description of the Related Art Thin film magnetic heads (hereinafter referred to as thin film heads) have been developed for the purpose of improving the recording density in magnetic disk drives. In this method, two thin magnetic films that serve as magnetic poles are formed on a substrate, separated from each other, and a coil is placed between them.
A gap is formed at the ends of two layers of magnetic films.
【０００３】図９は従来の磁気ディスク装置の要部を示
す概略ブロック図である。記録時にはライト制御信号が
与えられてライトゲート５が開き、ＮＲＺ の記録デー
タがライトゲート５を介してライト回路３に与えられ、
ここで記録電流に変換されて薄膜ヘッド１のコイル１ａ
に与えられる。そうするとコイル１ａと電磁的に結合さ
れた磁性膜間のギャップからの漏洩磁束により磁気ディ
スクに記録が行われる。再生時には薄膜ヘッド１に対す
る磁気ディスクの回転による磁束変化に応じた電流がコ
イル１ａに流れ、この電流がアンプ２で増幅され、復調
回路４で復調されて再生データが得られることとなる。FIG. 9 is a schematic block diagram showing the main parts of a conventional magnetic disk device. During recording, a write control signal is applied to open the write gate 5, and the NRZ recording data is applied to the write circuit 3 via the write gate 5.
Here, it is converted into a recording current and is converted into a coil 1a of the thin film head 1.
given to. Then, recording is performed on the magnetic disk by magnetic flux leaking from the gap between the magnetic film electromagnetically coupled to the coil 1a. During reproduction, a current flows through the coil 1a in accordance with changes in magnetic flux due to rotation of the magnetic disk relative to the thin film head 1, and this current is amplified by the amplifier 2 and demodulated by the demodulation circuit 4 to obtain reproduced data.
【０００４】0004
【発明が解決しようとする課題】このような薄膜ヘッド
を有する磁気ディスク装置では記録直後の再生時にポッ
プコーンノイズと称する瞬時的な高レベルの雑音が発生
するという問題点がある。これは記録時の磁化によって
移動した磁壁の一部が記録終了後にも不純物、欠陥の存
在のために不安定位置に残り、その後安定位置へ移動す
ることに因ると考えられている。これを解決する手段と
して斯かる磁壁移動が生じにくいようにすることが考え
られ、例えば特願平２−２７４５１３号が本願出願人に
より提案されている。A magnetic disk device having such a thin film head has a problem in that instantaneous high-level noise called popcorn noise is generated during reproduction immediately after recording. This is thought to be due to the fact that a part of the domain wall that has moved due to magnetization during recording remains at an unstable position even after recording is complete due to the presence of impurities and defects, and then moves to a stable position. As a means to solve this problem, it is possible to make such domain wall movement less likely to occur, and for example, Japanese Patent Application No. 2-274513 has been proposed by the applicant of the present invention.
【０００５】このような磁性膜による工夫はノイズ抑制
には有効である反面、記録再生効率に影響する。従って
記録再生効率に対する影響なしに記録直後の再生時にお
けるポップコーンノイズを防止することが薄膜ヘッド実
用化上の課題となっていた。本発明は斯かる課題を解決
すべくなされたものであり、記録直後の再生に先立ち、
強制的に磁壁を移動させることとして再生時のポップコ
ーンノイズを防止できる磁気記録装置を提供することを
目的とする。Although such efforts using magnetic films are effective in suppressing noise, they affect recording and reproducing efficiency. Therefore, it has been a challenge to prevent popcorn noise during playback immediately after recording without affecting the recording and playback efficiency when putting thin film heads into practical use. The present invention has been made to solve such problems, and prior to playback immediately after recording,
An object of the present invention is to provide a magnetic recording device that can prevent popcorn noise during reproduction by forcibly moving domain walls.
【０００６】[0006]
【課題を解決するための手段】図１は第１発明の磁気記
録装置の概略ブロック図である。記録データはライト制
御信号によって開閉制御されるライトゲート５を介して
ライト回路３に与えられ、ライト回路３で生成された電
流が薄膜ヘッド１のコイル１ａへ通流されるようにして
ある。一方、再生時にはコイル１ａに生じた誘導電流は
アンプ２によって増幅され、復調回路４で復調されて再
生データとなる。斯かる構成は従来のものと同様である
が、第１発明では交流電流発生回路６を備えており、こ
れが発生する微小な交流電流をコイル１ａに通流するよ
うにしてある。そのタイミングは例えばライト制御信号
に依っている。[Means for Solving the Problems] FIG. 1 is a schematic block diagram of a magnetic recording device according to the first invention. Recorded data is applied to the write circuit 3 via a write gate 5 whose opening and closing are controlled by a write control signal, and the current generated by the write circuit 3 is made to flow to the coil 1a of the thin film head 1. On the other hand, during reproduction, the induced current generated in the coil 1a is amplified by the amplifier 2 and demodulated by the demodulation circuit 4 to become reproduced data. Although this configuration is similar to the conventional one, the first invention is provided with an alternating current generating circuit 6, and a minute alternating current generated by this is made to flow through the coil 1a. The timing depends on the write control signal, for example.
【０００７】図２は第２発明の磁気記録装置の概略ブロ
ック図である。この装置は第１発明の交流電流発生回路
６に替えてパルス発生回路７を備えたものであり、これ
が発生するパルスをコイル１ａに通流するようにしてあ
る。その通流タイミングは例えばライト制御信号に依っ
ている。FIG. 2 is a schematic block diagram of a magnetic recording device according to the second invention. This device is equipped with a pulse generating circuit 7 in place of the alternating current generating circuit 6 of the first invention, and the pulses generated by this circuit are made to flow through the coil 1a. The timing of the current flow depends on, for example, a write control signal.
【０００８】[0008]
【作用】第１発明においては記録が終わった直後、つま
りライト制御信号消滅直後に交流電流発生回路６はコイ
ル１ａに交流電流を通流させる。これにより不安定な状
態の磁壁が安定状態へ移動し、記録に続く再生時に磁壁
移動を伴うポップコーンノイズを生じることがない。第
２発明においては記録が終わった直後、つまりライト制
御信号消滅直後に、パルス発生回路７は記録データの最
後のデータに係る電流と逆極性の電流をコイル１ａに通
流すべくパルスを発する。これにより同じく磁壁が移動
し、後続の再生時のポップコーンノイズ発生を防止でき
る。[Operation] In the first invention, immediately after recording ends, that is, immediately after the write control signal disappears, the alternating current generating circuit 6 causes an alternating current to flow through the coil 1a. As a result, the domain wall in an unstable state moves to a stable state, and popcorn noise accompanying domain wall movement does not occur during reproduction following recording. In the second invention, immediately after recording ends, that is, immediately after the write control signal disappears, the pulse generating circuit 7 generates a pulse to cause a current of opposite polarity to the current associated with the last data of the recorded data to flow through the coil 1a. As a result, the domain wall similarly moves, and it is possible to prevent popcorn noise from occurring during subsequent reproduction.
【０００９】[0009]
【実施例】以下本発明をその実施例を示す図面に基づい
て詳述する。図３は第１発明の磁気記録再生装置の要部
のブロック図である。図４（ａ） に示す如きＮＲＺ
の記録データがライトゲート５に与えられる。ライト制
御信号は図示しない記録媒体への書込時にハイレベルと
なる図４（ｂ） の如き信号であり、これをライトゲー
ト５に与えるようにしてある。ライトゲート５はこれを
受けると開いて記録データをライト回路３へ入力する。
ライト回路３は記録データを記録に必要な電流に変換し
て薄膜ヘッド１のコイル１ａへ与える。DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to drawings showing embodiments thereof. FIG. 3 is a block diagram of the main parts of the magnetic recording and reproducing apparatus of the first invention. NRZ as shown in Figure 4(a)
The recorded data is given to the write gate 5. The write control signal is a signal as shown in FIG. 4(b) which becomes high level when writing to a recording medium (not shown), and is applied to the write gate 5. When the write gate 5 receives this, it opens and inputs the recording data to the write circuit 3. The write circuit 3 converts the recording data into a current necessary for recording and supplies it to the coil 1a of the thin film head 1.
【００１０】再生時においてはコイル１ａに電流が誘導
され、これがアンプ２で増幅され、復調回路４で復調さ
れ再生データを得る。交流電流発生回路６はライト制御
信号（図４（ｂ））が入力される微分回路６１と、該微
分回路６１が出力する図４（ｃ） に示す微分信号のパ
ルスのうちライト制御信号の立下り側パルスのみを残し
て出力する整流回路６２と、整流回路６２出力によって
トリガされ、図４（ｄ） に示す如き交流電流を出力す
る発振回路６３とを備え、この発振回路６３出力をコイ
ル１ａへ与えるようにしてある。During reproduction, a current is induced in the coil 1a, which is amplified by the amplifier 2 and demodulated by the demodulation circuit 4 to obtain reproduced data. The alternating current generating circuit 6 includes a differentiating circuit 61 to which a write control signal (FIG. 4(b)) is input, and a differential signal output from the differentiating circuit 61 that detects the rising edge of the write control signal among the pulses of the differential signal shown in FIG. 4(c). It is equipped with a rectifier circuit 62 that outputs only the downstream pulses, and an oscillation circuit 63 that is triggered by the output of the rectifier circuit 62 and outputs an alternating current as shown in FIG. 4(d). It is intended to be given to
【００１１】発振回路６３出力は記録媒体への書込が行
われず、所期の磁壁移動が行われても、それ以外の障害
が生じないようなものでなければならない。従って第１
波のピーク値は不安定磁壁の移動には十分な値とするこ
とは言うまでもないが、また交流通流による磁気媒体へ
の重ね書き （記録データの変化） が実質的に生じな
いようにその周波数は最高記録周波数以上とする。更に
再生に影響を与えないように通流時間は最小回転待ち時
間以下とする。更にまた、図４（ｄ） に示すように漸
減交流を通流することとして磁性膜に残留磁気が生じな
いようにするのが望ましい。The output of the oscillation circuit 63 must be such that even if writing to the recording medium is not performed and the intended domain wall movement is performed, no other disturbances occur. Therefore, the first
Needless to say, the peak value of the wave should be set to a value sufficient to move the unstable domain wall, but the frequency should also be set so that overwriting (change in recorded data) on the magnetic medium due to AC current does not substantially occur. shall be higher than the highest recording frequency. Furthermore, the flow time is set to be less than or equal to the minimum rotation waiting time so as not to affect regeneration. Furthermore, as shown in FIG. 4(d), it is desirable to pass a gradually decreasing alternating current so that residual magnetism does not occur in the magnetic film.
【００１２】図５は第２実施例を示す。この第２実施例
は交流電流発生回路８の起動にトラック位置信号を用い
ることとしている。記録が終了すると再生のために薄膜
ヘッド１はシーク動作に入る。このためトラック位置信
号は次々とトラック番号の変化する信号となる。交流電
流発生回路８はこのようなトラック番号の変化を判別す
る回路と、該回路がトラック間を移動中であることの判
定信号を出している間に交流電流を発生するようにした
発振回路とから構成される。このような実施例による場
合は薄膜ヘッドがトラック間を移動する間に交流電流を
コイル１ａに通流するので、この電流による重ね書きの
可能性が極めて低くなる。従って交流電流の周波数又は
ピーク値に関しての制約が緩和される。FIG. 5 shows a second embodiment. In this second embodiment, a track position signal is used to start up the alternating current generating circuit 8. When recording is completed, the thin film head 1 enters a seek operation for reproduction. Therefore, the track position signal becomes a signal in which the track number changes one after another. The alternating current generating circuit 8 includes a circuit for determining such a change in track number, and an oscillation circuit for generating an alternating current while the circuit is outputting a determination signal indicating that the circuit is moving between tracks. It consists of In this embodiment, since an alternating current is passed through the coil 1a while the thin film head moves between tracks, the possibility of overwriting due to this current is extremely low. Therefore, restrictions on the frequency or peak value of the alternating current are relaxed.
【００１３】図６は第３実施例を示す。この第３実施例
は交流電流発生回路９の起動にセクタ位置信号を用いる
こととしている。セクタ位置信号は薄膜ヘッド１がセク
タ間ギャップを通過する場合に特有の信号を発する。交
流電流発生回路９はこのような信号を判別する回路と、
該回路が当該信号を判別して所定信号を出力している間
に交流電流を発生するようにした発振回路とから構成さ
れる。このような実施例による場合はセクタ間ギャップ
の移動の間に交流電流をコイルに通流するので、この電
流による重ね書きの可能性は極めて低くなる。従って第
２実施例同様交流電流の周波数又はピーク値に関しての
制約が緩和される。FIG. 6 shows a third embodiment. In this third embodiment, a sector position signal is used to start up the alternating current generating circuit 9. The sector position signal emits a specific signal when the thin film head 1 passes through an inter-sector gap. The alternating current generating circuit 9 includes a circuit for determining such a signal, and
The oscillation circuit generates an alternating current while the circuit discriminates the signal and outputs a predetermined signal. In this embodiment, since an alternating current is passed through the coil during movement of the inter-sector gap, the possibility of overwriting due to this current is extremely low. Therefore, as in the second embodiment, restrictions on the frequency or peak value of the alternating current are relaxed.
【００１４】次に第２発明の実施例について説明する。
第２発明の装置は、図３に示す第１発明の装置の交流電
流発生回路６をパルス発生回路７に置換えたものである
。パルス発生回路７はライト制御信号（図８（ｂ））が
入力される微分回路７１と、該微分回路７１が出力する
図８（ｃ） に示す微分信号のパルスのうちライト制御
信号の立下り側パルスのみを残して出力する整流回路７
２と、整流回路７２出力によってトリガされる単安定マ
ルチバイブレータ回路７３とからなる。単安定マルチバ
イブレータ回路７３は整流回路７２出力によりトリガさ
れる２つの単安定マルチバイブレータを備え、一方が正
極性のパルスを、他方は負極性のパルスを出力する。Next, an embodiment of the second invention will be described. The device of the second invention is obtained by replacing the alternating current generating circuit 6 of the device of the first invention shown in FIG. 3 with a pulse generating circuit 7. The pulse generation circuit 7 includes a differentiating circuit 71 to which a write control signal (FIG. 8(b)) is input, and a falling edge of the write control signal among the pulses of the differential signal output from the differentiating circuit 71 shown in FIG. 8(c). Rectifier circuit 7 that outputs only the side pulses
2, and a monostable multivibrator circuit 73 triggered by the output of the rectifier circuit 72. The monostable multivibrator circuit 73 includes two monostable multivibrators triggered by the output of the rectifier circuit 72, one of which outputs a pulse of positive polarity and the other of which outputs a pulse of negative polarity.
【００１５】出力パルスの振幅は記録データに対応して
ライト回路３からコイル１ａに流される電流の振幅より
小さく、不安定磁壁の移動に有効な範囲のレベルに設定
されている。また時間幅は記録データ （図８（ａ））
のパルス幅以下とし重ね書きを防止する。単安定マルチ
バイブレータ回路７３には記録データが入力されており
、最後のデータに係る電流と逆極性の方のパルスのみを
コイル１ａへ通流せしめるゲート回路を備える。図８（
ａ） に示すように記録データの最後の電流が正極性で
あった場合はパルス発生回路７の出力は図８（ｄ） の
ように負極性となる。
この第２発明におけるパルス電流通流タイミングの制御
にもトラック位置信号、セクタ位置信号を用いることが
できる。The amplitude of the output pulse is smaller than the amplitude of the current flowing from the write circuit 3 to the coil 1a in accordance with the recording data, and is set to a level within a range effective for moving the unstable domain wall. Also, the time width is the recorded data (Figure 8 (a))
pulse width or less to prevent overwriting. Recorded data is input to the monostable multivibrator circuit 73, which includes a gate circuit that allows only a pulse having a polarity opposite to the current associated with the last data to flow through the coil 1a. Figure 8 (
If the last current of recorded data is of positive polarity as shown in a), the output of the pulse generating circuit 7 becomes negative as shown in FIG. 8(d). The track position signal and the sector position signal can also be used to control the pulse current flow timing in this second invention.
【００１６】[0016]
【発明の効果】以上の如き本発明による場合は記録直後
又は記録再生に関係がないタイミングで不安定状態にあ
る磁壁を強制的に移動させるのでこれに続く再生時にポ
ップコーンノイズが発生することがない。従って再生デ
ータの信頼性が高まる。また、この発明では薄膜ヘッド
の構成上の特殊性がないので効率面での不利がないなど
、本発明は優れた効果を奏する。なお、本発明は磁気デ
ィスク装置に限らず他の磁気記録装置にも適用できる。[Effects of the Invention] In the case of the present invention as described above, since the domain wall in an unstable state is forcibly moved immediately after recording or at a timing unrelated to recording and reproduction, popcorn noise does not occur during subsequent reproduction. . Therefore, the reliability of reproduced data is increased. Further, since there is no special feature in the structure of the thin film head, the present invention has excellent effects such as no disadvantage in terms of efficiency. Note that the present invention is applicable not only to magnetic disk devices but also to other magnetic recording devices.
【図１】第１発明の装置の概略ブロック図である。FIG. 1 is a schematic block diagram of a device of a first invention.
【図２】第２発明の装置の概略ブロック図である。FIG. 2 is a schematic block diagram of a device according to a second invention.
【図３】第１発明の装置要部のブロック図である。FIG. 3 is a block diagram of main parts of the device of the first invention.
【図４】第１発明の装置のタイムチャートである。FIG. 4 is a time chart of the device of the first invention.
【図５】第１発明の第２実施例の概略ブロック図である
。FIG. 5 is a schematic block diagram of a second embodiment of the first invention.
【図６】第１発明の第３実施例の概略ブロック図である
。FIG. 6 is a schematic block diagram of a third embodiment of the first invention.
【図７】第２発明の装置要部のブロック図である。FIG. 7 is a block diagram of main parts of the device of the second invention.
【図８】第２発明の装置のタイムチャートである。FIG. 8 is a time chart of the device of the second invention.
【図９】従来の磁気ディスク装置の概略ブロック図であ
る。FIG. 9 is a schematic block diagram of a conventional magnetic disk device.
１ 薄膜ヘッド １ａ コイル ６，８，９ 交流電流発生回路 1 Thin film head 1a Coil 6, 8, 9 AC current generation circuit
Claims (2)
的に結合させたコイル（１ａ）とを備える薄膜磁気ヘッ
ドを用い、該コイルを流れる電流に関連して記録，再生
を行う磁気記録再生装置において、非記録時に前記コイ
ルに通流すべき交流の電源（６）を有することを特徴と
する磁気記録再生装置。1. A magnetic head that uses a thin film magnetic head comprising a magnetic film serving as a magnetic pole and a coil (1a) electromagnetically coupled to the magnetic film, and performs recording and reproduction in relation to a current flowing through the coil. A magnetic recording and reproducing apparatus characterized in that the recording and reproducing apparatus comprises an alternating current power source (6) to be applied to the coil during non-recording.
的に結合させたコイル（１ａ）とを備える薄膜磁気ヘッ
ドを用い、該コイルに正負に交互的に変化するパルス電
流を，通流させて磁気記録媒体にデータを記録し、また
磁気記録媒体によってコイルに電流を生ぜしめて記録デ
ータを再生する磁気記録再生装置において、記録から再
生に移行する間に、記録時の最後のデータに係る電流と
逆極性の電流を通流させる手段（７）を備えることを特
徴とする磁気記録再生装置。2. A thin film magnetic head comprising a magnetic film serving as a magnetic pole and a coil (1a) electromagnetically coupled to the magnetic film is used, and a pulse current that alternately changes between positive and negative is passed through the coil. In a magnetic recording and reproducing device that records data on a magnetic recording medium by causing a current to flow through the magnetic recording medium and reproduces the recorded data by generating a current in a coil by the magnetic recording medium, during the transition from recording to reproduction, the last data at the time of recording is A magnetic recording/reproducing apparatus characterized by comprising means (7) for passing a current having a polarity opposite to that of the above current.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5252091A JPH04286701A (en) | 1991-03-18 | 1991-03-18 | Magnetic recording and reproducing device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5252091A JPH04286701A (en) | 1991-03-18 | 1991-03-18 | Magnetic recording and reproducing device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH04286701A true JPH04286701A (en) | 1992-10-12 |
Family
ID=12917021
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP5252091A Withdrawn JPH04286701A (en) | 1991-03-18 | 1991-03-18 | Magnetic recording and reproducing device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH04286701A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5963385A (en) * | 1993-09-17 | 1999-10-05 | Fujitsu Limited | Magnetic recording/reproducing apparatus and method for supplying a current to a magnetic head to stabilize a magnetized state of a magnet pole |
| US6587295B1 (en) * | 1999-12-13 | 2003-07-01 | Tdk Corporation | Method, apparatus, system and computer process for improving property of thin-film magnetic head |
-
1991
- 1991-03-18 JP JP5252091A patent/JPH04286701A/en not_active Withdrawn
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5963385A (en) * | 1993-09-17 | 1999-10-05 | Fujitsu Limited | Magnetic recording/reproducing apparatus and method for supplying a current to a magnetic head to stabilize a magnetized state of a magnet pole |
| US6038093A (en) * | 1993-09-17 | 2000-03-14 | Fujitsu Limited | Magnetic recording/reproducing apparatus with a current supplying circuit for demagnetizing residual magnetization remaining at an end of a magnetic pole |
| US6587295B1 (en) * | 1999-12-13 | 2003-07-01 | Tdk Corporation | Method, apparatus, system and computer process for improving property of thin-film magnetic head |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A300 | Application deemed to be withdrawn because no request for examination was validly filed |
Free format text: JAPANESE INTERMEDIATE CODE: A300 Effective date: 19980514 |