US 6,686,734 B2 · System and method for non-destructive measurement of dynamic coercivity effects

Abstract

A method for non-destructive measurement of dynamic coercivity is disclosed. In this method, magnetic media is DC erased by applying a forward DC magnetic field to the magnetic media such that the magnetic moments in the magnetic media are substantially aligned. A specified number of reversed magnetic field pulses are then applied to the magnetic media in a direction opposite to the forward DC magnetic field, wherein the intensity of the reversed magnetic field pulses is less than the remanent coercivity of the magnetic media. The broadband medium noise of the magnetic media is measured. The intensity of the reversed magnetic field pulses is then repeatedly and incrementally increased and applied to the write head for the specified number of pulses, the intensity of the reversed magnetic field pulses eventually exceeding the remanent coercivity of the magnetic media. For each intensity level of the reversed magnetic field pulses, the broadband medium noise is again measured. The coercivity of the magnetic media is derived from the reversed magnetic field pulse intensity at which the broadband medium noise is a maximum. The entire process may be repeated for different numbers of pulses in order to measure dynamic coercivity.

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Claims1

Dependent claims

A system for non-destructive measurement of dynamic coercivity of magnetic media, the system comprising:

a read/write head for non-destructively writing to and reading from magnetic media;
and
means for measuring dynamic coercivity by using reverse DC erased noise as an indicator for coercivity.

Dependencies are inferred from the claim text.

Description3,969 words

Summary971 words

#1. Field of the Invention

#Embodiments of this invention relate generally to the measurement of dynamic coercivity effects in magnetic media, and in particular embodiments to methods for non-destructive measurement of dynamic coercivity effects in magnetic media, and systems incorporating the same.

#2. Description of Related Art

Brief description of the drawings8 figures

#FIG. 1 is a schematic diagram of a system for non-destructive measurement of dynamic coercivity effects in magnetic media according to an embodiment of the present invention.

#FIG. 2 illustrates the DC erasing of a track according to an embodiment of the invention.

#FIG. 3 illustrates partial reverse DC erasing of a track according to an embodiment of the invention.

Detailed description2,818 words

#In the following description of preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the preferred embodiments of the present invention.

#As the recording media industry strives for increasingly smaller disk drives with increasingly larger storage capability, the areal density (the number of bits, or magnetic flux reversals, per inch) of magnetic disks continues to increase. In order to maintain a sufficient signal-to-noise ratio, the number of magnetizable units in each stored bit must be kept above a certain minimum value. To reduce bit size while maintaining a certain number of magnetizable units in each bit, the size of the magnetizable units (the particle or crystal grain size) must therefore be correspondingly decreased.

#However, very small magnetic particles are characterized by low coercivity (the ability of a particle to resist magnetic change) and low remanent coercivity (the magnetic field required to reduce the magnetization of the particle to zero), and as a result, tend to be magnetically unstable.

Facts

Application

09/900,226Filed 6 Jul 2001 · continuation

Priority

11 Dec 1997

Published

US 2001/0040448 A115 Nov 2001

Granted

3 Feb 2004

Term ended

29 Mar 2019

Estimated · how

20 years from earliest known nonprovisional domestic filing plus recorded patent term adjustment, including 153 days of adjustment. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification2 codes

G01R 33/1207
Measuring magnetic properties of articles or specimens of solids or fluids: testing individual magnetic storage devices, e.g. records carriers or…
G01R
Measuring electric variables

Family

Application60/069,197Us provisional application · filed 11 Dec 1997

Application09/179,297Parent of this continuation · filed 27 Oct 1998

US 2001/0040448 A1Pre-grant publication · published 15 Nov 2001

US 6,304,081 B1Parent of this continuation

US 6,686,734 B2This patent

From the US filing history. Foreign family members aren’t listed.

Timeline

11 Dec 1997Priority claimedParent application 60/069,197
6 Jul 2001Application filedUS 09/900,226
15 Nov 2001PublishedUS 2001/0040448 A1
5 Aug 2002Assigned to Jpmorgan Chase Bank, AS Collateral Agentsecurity agreement
3 Feb 2004GrantedUS 6,686,734 B2
3 Jan 2006Assigned to Seagate Technology LLCrelease of security interests in patent rights
15 May 2009Assigned to Jpmorgan Chase Bank, N.A., AS Administrative Agent and First Priority Representative, Wells Fargo Bank, National Association, AS Collateral Agent and Second Priority Representativesecurity agreement
19 Jan 2011Assigned to Seagate Technology Hdd Holdings, Maxtor Corporation, Seagate Technology LLC, Seagate Technology Internationalrelease
24 Mar 2011Assigned to The Bank of Nova Scotia, AS Administrative Agentsecurity agreement
15 Oct 2012Assigned to The Bank of Nova Scotia, AS Administrative Agentsecurity agreement
15 Oct 2012Assigned to Wells Fargo Bank, National Association, AS Collateral Agentsecond lien patent security agreement
19 Jul 2013Assigned to Seagate Technology LLC, Evault Inc. (F/K/A I365 Inc.), Seagate Technology International, Seagate Technology US Holdings, Inc.termination and release of security interest in patent rights
29 Mar 2019Term endedEstimated, includes 153 days of adjustment
20 May 2024Assigned to Seagate Technology LLC, Evault, Inc. (F/K/A I365 Inc.), Seagate Technology US Holdings, Inc.release of security interest
23 Jul 2024Assigned to Seagate Technology LLC, Evault Increlease of security interest
28 Feb 2025Assigned to Seagate Technology US Holdings, Inc., Evault, Inc. (F/K/A I365 Inc.), Seagate Technology LLCrelease of security interest
23 Jul 2025Assigned to Seagate Technology Public Limited Company, Seagate Technology, Seagate Technology Hdd Holdings, I365 Inc., Seagate Technology LLC, Seagate Technology International, Seagate Hdd Cayman, Seagate Technology (US) Holdings, Inc.release of security interest

System and method for non-destructive measurement of dynamic coercivity effects

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System and method for non-destructive measurement of dynamic coercivity effects

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims1

Description3,969 words

Drawings

Classification2 codes

Life of this patent

Description3,969 words