CA1253618A - Return-to-zero magnetic recording system - Google Patents
Return-to-zero magnetic recording systemInfo
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- CA1253618A CA1253618A CA000513651A CA513651A CA1253618A CA 1253618 A CA1253618 A CA 1253618A CA 000513651 A CA000513651 A CA 000513651A CA 513651 A CA513651 A CA 513651A CA 1253618 A CA1253618 A CA 1253618A
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- recording medium
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Abstract
RETURN TO ZERO VERTICAL MAGNETIC RECORDING SYSTEM
Abstract of the Disclosure An return-to-zero (RZ) vertical digital magnetic recording method and apparatus comprising a selectively magnetizable recording medium which includes a recording layer of magnetic material having a low vertical remanence. A magnetic recording head is positioned in close proximity to the recording medium, and relative motion is produced between the recording medium and the recording head. To record data, the recording head is energized with one short duration current pulse for each unit of data to be recorded. The resulting bipolar magnetic write field closes substantially perpendicular through the recording medium thereby producing, in the medium, a similarly bipolar flux configuration having the magnetic transition centered about the gap of the magnetic recording head. Data is represented by the transition in RZ vertical magnetic recording.
Abstract of the Disclosure An return-to-zero (RZ) vertical digital magnetic recording method and apparatus comprising a selectively magnetizable recording medium which includes a recording layer of magnetic material having a low vertical remanence. A magnetic recording head is positioned in close proximity to the recording medium, and relative motion is produced between the recording medium and the recording head. To record data, the recording head is energized with one short duration current pulse for each unit of data to be recorded. The resulting bipolar magnetic write field closes substantially perpendicular through the recording medium thereby producing, in the medium, a similarly bipolar flux configuration having the magnetic transition centered about the gap of the magnetic recording head. Data is represented by the transition in RZ vertical magnetic recording.
Description
~ ~'253~
RETURN TO Z~RO VERTIC.~u ~GNET~C RECORDING SYSTEM
~escription sackground Of ~he Invention Field Of The Invention The invention relates to magnetic recording and more particularly to a vertical recording method and apparatus~
Description Of The Prior Art Present efforts in vertical digital magnetic recording are based on the non-return-to-zero (NR2) recording method. In this mode, the magnetic medium is saturated between magnetic transitions with the unidirectional write field from the trailing edge of the recording head. When this ~ield is reversed, a transition is written. The NRZ mode is ideally suited and hence is in general use for horizontal digital recording. However, the NRZ mode of recording is not as suitable for vertical digital magnetic recording since this mode cannot fully utilize the performance potential of the vertical recording system either in terms of output signal or with respect to recording density.
Summary of the Invention It is therefore the principle object of the invention to provide a vertical recording method and apparatus which is operable in an return-to-zero ~RZ) mode.
. . .
In accordance with the invention, a vert-cal recording method and apparatus comprises a selectiv~ly magnetizable recording medium ?5 ~having a recording layer of magnetic material having low vertical ~remanence preferably on a high permeability underlayer, a mag-netic recording head having a recording gap in close pro~imity to the recording medium, means to produce relative motion between the rec~rding medium and the recording head, and ~means for supplylng signals representing information to the recording head.
The signals comprise one unidirec~ional current pulse for each unit of information to be recorded. The resulting bipolar magnetic write field closes substantially perpendicular through the surface of the recording medium so that the maqnetic flu~
sP.98acog ~2~36~
passes transversely through ~e recording layer of the recording medium whereby a bipoLar magn~.ic recording is produced in an R~
vertical recording mode centered about the gap of the magnet c recording head.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred emhodiment of the invention as illu~-trated in the accompanying drawings.
Brief Description of the Drawings FIG. 1 is a schematic block diagram of the apparatus used IO
practice the method comprisin~ the present invention.
; FIG. 2 is a section view of a specific embodiment of the magnetic read/write head of FIG. 1.
FIG. 3a is a plot of current supplied to the magnetic read/write head versus time for the present invention in the RZ mode and FIG. 3b is a similar plot for a magnetic read/write head operated in the prior art NRZ mode.
FIG. 4 is a diagram showing the preferred embodiment of the vertical recording medium according to the present invention.
, , 20 FIG. 5 is a diagram showing the write field configuration pro-~duced in response to the current drive pulse of FIG. 3a.
~:, FIG. 6 is a diagram showing the recorded RZ transition produced in the vertical recording medium as a result of the write field configuration of FIG. 5.
FIG. 7 is a table showing a comparison of write current, write field, magnetic response and recorded transition for recording in the NRZ mode for both horizontal and vertical recording, and in the RZ vertical mode.
FIG. 8 is a sketch showing the magnetization configuration abou_ two adjacent transitions written with (a~ write pulses of single polarity and (b) write pulses of alternating polarity.
S~984009 2 ~L2536~
iiG. 9 is a sketch showing ~ sequence of RZ recording events in t~e alternating and single p~larity mode.
FIG. 10 is a graph showing recording densities in the RZ vertical recording alternating mode for different head geometri2s and S length of write pulse (T).
Description of the Preferred ~mbodiments With reference to FIG~ 1 depicting a preferred embodiment of the apparatus for carrying out the invention, a digital data source 10 supplies digital data signals suitable for "return to zero~' (RZ) vertical recording to write driver 12. The write driver 12 generates a pulse of write current representing the data signals, and this write current is coupled to energize magnetic read/write head 14 to produce RZ ver~ically recorded transitions in a magnetic recording medium 16 suitable for RZ vertical recording.
Magnetic read/write head 14 is also used to read previously RZ
vertically recorded data from magnetic recording medium 16, and the read data signals are coupled to read char.nel 13 in which Ihe read data signals are amplified and processed to identify the ~Z
vertically recorded digital data which was previously recorded.
Any magnetic readtwrite head and magnetic recording medit~m suitable ~or RZ vertical recording can be used. A specific embodiment o~ the RZ vertical recording magnetic read/write head 14 and the RZ vertical magnetic recording medium 16 is shown in FlGo 2. The magnetic head 1~ shown in FIG. 2 is a thin film magnetic head which is formed on a nonmagnetic ceramic substrate 2CI, as is known in the art. After deposition o~ the thin rilm structure, the substrate is formed to provide an air bearing surface 22, which may be cylindrical, tapered, taper-flat, or of sc,me other geometry. The thin film structure includes magr.etic pole pieces 24 and 26 and a ~inding 28 having at least one turn.
Pole pieces 24 and 26 are s~parated by a small distance at air bearing surface 22 to produce a transducing gap 30~ ~hen ~indin~
2S is energized with a suita~le write current pulse, a recording magnetic field is produced at transducing gap 30.
The embodiment ~ the RZ vertical magnetic recording medium ;~
shown in FIG. 2 comprises a nonmagnetic substrate 32 and a soft magnetic underlayer 34 deposited on the substrate 32 below the magnetic recording layer 36. The RZ vertical recording medium lo S~984009 3 ~Z5i3~
.
according to the invention preferably has a smaller coercivity and hence vertical remanence than is typically used in conven-tional vertical recordincJ.
Typical ranges are siven in T~ble 1 for the saturation magnetiza-tion, 4~Ms, vertical remanence, Mr/MS and vertical coercivity Hc for vertical recording media for reported usage in the NRZ moàe and the workable parameters for the RZ vertical recording of tY~e present invention.
T~BLE I
Typical Mediu~ Characteristics Vertical Recording Media - -NRZ RZ
4~Ms2000-6000 4000-10000 Gauss ~ r/MS30-80 2-20 %
i~
Hc 600-1200 200-800 Oe `~ :
:~
The preferxed embocliment of the RZ vertical recording medium is shown in FIG. 4. The mediurn comprises a nonmagnetic substrate 32, a high permeability underlayer 34 and the low coercivity RZ
recording layer 36. The medium is DC erased prior to recordirg to produce the magnetization configuration shown by the arrows in the drawing (FIG. 4). When the RZ vertical recording magnetic -read/write head 14 is energized with a unidirec~ional current pulse (see FIG. 3a) a write field configuration is produced as shown in FIG. 5. This bipolar write field closes substantially ~5 perpendicular to the surface of the recording medium and s centered about the transducing gap 30 of the recording head 14 as shown by the centerline of s~mmetry 31. The resulting recorded transition is also centered ~bout the gap 30 as sho~.m in FIG. 6.
.
The recording method according to the invention utilizes vertical recording in a RZ mode. To produce recording in the RZ vertical `jrecording mode it is necessary to use a short pulse of wrile current instead of polarity reversals, as used in the prior art "non return to zero" NRZ recording mode. This is illustrated in ~, S~984009 4 ~2~;36~
\
FIG. 3b in which the NRZ write current is ON at some selected level I
all the time, and to write a transition, the polarity of the write current is reversed. As shown in FIG. 3b at time t=tO the write current is at +I, and at time t=tl, the polarity of the write current is switched to -I to write a first transition. At t=t2, the polarity of the write current is again switched to +I to write a second transition.
In contrast to this operation, FIG. 3a shows write current for the RZ
vertical recording mode at zero at time t=t0, and the write current remains at zero until time t=tl. At this time a short pulse of write current with pulse length T and amplitude I is produced to record a first transition. The write current then returns to zero until a second short pulse of write current, with pulse length T, is produced at time t=t2 to produce a second transition. The write current for the RZ
vertical recording mode is a short pulse of current, and the write process takes place symmetrically about the gap region of the head. The associated write field has bipolar symmetry and has a spatial extent directly governed by the pole piece geometry. In this context, bipolar describes a magne~ic field or magnetic flux centered about the transducing gap having on one side an excursion in the upward direction and on the other side a substantially equal excursion in the downward direction with respect to the plane of the recording medium. The data bits recorded in the recording medium 16 in response to the short pulses of current have a symmetric bipolar magnetization configuration~ and have their size limited by internal demagnetiz~ng fields.
The RZ vertical recording system embodying the invention has the advantages of not only lower write current but also of increased linear storage density. The resulting output signal is improved in both amplitude and wave form. In addition, since the vertical magnetization vanishes between data bits in the RZ vertical recording method according to the invention, a variety of options are available for data encoding.
To contrast the operation according to the RZ vertical recording according to the present invention, FIG. 4 provides a comparative overview of NRZ and RZ recording principles when used with horizontal and vertical rscording modes. For each of these modes, the table shows the write current and relative head/medium position for writing an isolated transition, the write field 36~l8 profile with the portion effecting the transition accentuated, the response of the magnetization at time t=tO, and the remanent magnetization after the head has passed.
Of the techniques shown in FIG. 4, NRZ horizontal and NRZ vertical are the conventional methods, and the RZ vertical method is the method of the present invention. The RZ horizontal method is not viable since there exists no demagnetizing effect to quench the remanent magnetization away from the transition.
For the RZ vertical recording method, it can be seen that a transition is produced which not only is symmetrical but also is sharper. The transition is sharper because the write field gradients below the gap are substantially larger than that gradient below the heads' trailing edge which is used with NRZ recording.
It has been shown that a short pulse of write current in the vertical recording mode produces advantageous operation when considering isolated data bits. Since the vertical magnetization vanishes between data bits in the RZ vertical recording method, some options are available for data encoding. Since it is desired to select an encoding option which produces the greatest recording density, these options will be considered.
There are three options for data encoding. A first option is with single polarity write pulses, in which data is encoded by the presence or absence of a pulse. A second option is with alternating polarity write pulses, in which data is encoded by having a positive or negative pulse. A third option allows for data encoding using ternary, bipolar write pulses, in which data is encoded by having no pulse, a positive pulse, or a negative pulse. The first two of these options are examined with the aid of FIG. 9, which analyzes a write sequence consisting of two pulses of alternating polarity (a) and alternatively, two single polarity (b) pulses. Pulse width is Tl. The spacing between pulses is T2. Time instances of interest labelled tl through t7. For each of these instances, the figure shows the corresponding head position, the write field profile (dashed curve), and the response of the magnetization. It is assumed that the medium has previously been DC
erased, leaving the small uniform remanent magnetization evident in the "tl". In the encoding method shown in FIG. 6, information is defined by the presence (1) or absence . ., ~536~13 ~, (0) of a pulse, but other encoding methods could be used. At t2, the flrst write pulse is applied, producing the depicted transition. While the pulse is one, this transition remains stationary relative to the wri~e field, propagating along the medium at the velocity, v. At t3, which marks the trailing edge of the pulse, the transition freezes in the medium, while, because of the demagnetizing fields, there occurs some slimming of the transition profile. The location of its formation has now moved a distance sl=vxTl from the recording head.
The second write pulse occurs at t4. Between t3 and t4 the bit moved a distance s2=vxT2. Let us find the minimum pulse spacing, T2, such that the write field of the second pulse does not affect the previously recorded bit. This minimum separation must depend on the spatial extent of the write field. For the sake of a simple argument, we assume that the effective write field extends just to the outer edge of the pole pieces and that the shoulders of a written magnetization profile have the same spatial extent. Then, at t5, the leading edge of the second write pulse, the head needs to be separated from the recorded bit at least by a distance: (single polarity) s2=(2p+g); (alternating polarity) s2=(p+g); where g and p are the length of the gap and the pole pieces, respectively. This minimum separation defines T2=s2/v, the min.
spacing between write pulses. By t6, the second transition freezes in the medium. The final illustration, at t7, shows both transitions recorded and moving with the medium.
From above, the minimum separation between adjacent data bits is:
s=vT+(2p+g), for the single polarity sequence, and s=vT+(lp+g), for the alternating polarity sequence In the RZ mode, the attainable recording density is limited by head geometry, medium velocity and duration of the write pulse, as shown in FIG. 10. This figure shows reciprocal bit spacing as a function of medium velocity for two different head geometries and two different pulse lengths. From FIG. 10 it can be seen that the attainable density is predominantly limited, at lower media velocities, by head geometry and, at higher media velocities, by the length of the write pulses.
. ..
In suitable systems, vertical recording in the RZ mode provides improvements in linear density as well as in the amplitude and ` ~253~
waveform of the output signal. In terms of the write process, the RZ
mode utilizes write field reductions which permit the use of much simplified write head configurations. With regard to the medium, the RZ
method opens up a new approach to the design of recording media.
Improvements in recording density do not have to rely on further increases of coercivity, but instead, are sought through a judicious choice of media characteristics.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.
RETURN TO Z~RO VERTIC.~u ~GNET~C RECORDING SYSTEM
~escription sackground Of ~he Invention Field Of The Invention The invention relates to magnetic recording and more particularly to a vertical recording method and apparatus~
Description Of The Prior Art Present efforts in vertical digital magnetic recording are based on the non-return-to-zero (NR2) recording method. In this mode, the magnetic medium is saturated between magnetic transitions with the unidirectional write field from the trailing edge of the recording head. When this ~ield is reversed, a transition is written. The NRZ mode is ideally suited and hence is in general use for horizontal digital recording. However, the NRZ mode of recording is not as suitable for vertical digital magnetic recording since this mode cannot fully utilize the performance potential of the vertical recording system either in terms of output signal or with respect to recording density.
Summary of the Invention It is therefore the principle object of the invention to provide a vertical recording method and apparatus which is operable in an return-to-zero ~RZ) mode.
. . .
In accordance with the invention, a vert-cal recording method and apparatus comprises a selectiv~ly magnetizable recording medium ?5 ~having a recording layer of magnetic material having low vertical ~remanence preferably on a high permeability underlayer, a mag-netic recording head having a recording gap in close pro~imity to the recording medium, means to produce relative motion between the rec~rding medium and the recording head, and ~means for supplylng signals representing information to the recording head.
The signals comprise one unidirec~ional current pulse for each unit of information to be recorded. The resulting bipolar magnetic write field closes substantially perpendicular through the surface of the recording medium so that the maqnetic flu~
sP.98acog ~2~36~
passes transversely through ~e recording layer of the recording medium whereby a bipoLar magn~.ic recording is produced in an R~
vertical recording mode centered about the gap of the magnet c recording head.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred emhodiment of the invention as illu~-trated in the accompanying drawings.
Brief Description of the Drawings FIG. 1 is a schematic block diagram of the apparatus used IO
practice the method comprisin~ the present invention.
; FIG. 2 is a section view of a specific embodiment of the magnetic read/write head of FIG. 1.
FIG. 3a is a plot of current supplied to the magnetic read/write head versus time for the present invention in the RZ mode and FIG. 3b is a similar plot for a magnetic read/write head operated in the prior art NRZ mode.
FIG. 4 is a diagram showing the preferred embodiment of the vertical recording medium according to the present invention.
, , 20 FIG. 5 is a diagram showing the write field configuration pro-~duced in response to the current drive pulse of FIG. 3a.
~:, FIG. 6 is a diagram showing the recorded RZ transition produced in the vertical recording medium as a result of the write field configuration of FIG. 5.
FIG. 7 is a table showing a comparison of write current, write field, magnetic response and recorded transition for recording in the NRZ mode for both horizontal and vertical recording, and in the RZ vertical mode.
FIG. 8 is a sketch showing the magnetization configuration abou_ two adjacent transitions written with (a~ write pulses of single polarity and (b) write pulses of alternating polarity.
S~984009 2 ~L2536~
iiG. 9 is a sketch showing ~ sequence of RZ recording events in t~e alternating and single p~larity mode.
FIG. 10 is a graph showing recording densities in the RZ vertical recording alternating mode for different head geometri2s and S length of write pulse (T).
Description of the Preferred ~mbodiments With reference to FIG~ 1 depicting a preferred embodiment of the apparatus for carrying out the invention, a digital data source 10 supplies digital data signals suitable for "return to zero~' (RZ) vertical recording to write driver 12. The write driver 12 generates a pulse of write current representing the data signals, and this write current is coupled to energize magnetic read/write head 14 to produce RZ ver~ically recorded transitions in a magnetic recording medium 16 suitable for RZ vertical recording.
Magnetic read/write head 14 is also used to read previously RZ
vertically recorded data from magnetic recording medium 16, and the read data signals are coupled to read char.nel 13 in which Ihe read data signals are amplified and processed to identify the ~Z
vertically recorded digital data which was previously recorded.
Any magnetic readtwrite head and magnetic recording medit~m suitable ~or RZ vertical recording can be used. A specific embodiment o~ the RZ vertical recording magnetic read/write head 14 and the RZ vertical magnetic recording medium 16 is shown in FlGo 2. The magnetic head 1~ shown in FIG. 2 is a thin film magnetic head which is formed on a nonmagnetic ceramic substrate 2CI, as is known in the art. After deposition o~ the thin rilm structure, the substrate is formed to provide an air bearing surface 22, which may be cylindrical, tapered, taper-flat, or of sc,me other geometry. The thin film structure includes magr.etic pole pieces 24 and 26 and a ~inding 28 having at least one turn.
Pole pieces 24 and 26 are s~parated by a small distance at air bearing surface 22 to produce a transducing gap 30~ ~hen ~indin~
2S is energized with a suita~le write current pulse, a recording magnetic field is produced at transducing gap 30.
The embodiment ~ the RZ vertical magnetic recording medium ;~
shown in FIG. 2 comprises a nonmagnetic substrate 32 and a soft magnetic underlayer 34 deposited on the substrate 32 below the magnetic recording layer 36. The RZ vertical recording medium lo S~984009 3 ~Z5i3~
.
according to the invention preferably has a smaller coercivity and hence vertical remanence than is typically used in conven-tional vertical recordincJ.
Typical ranges are siven in T~ble 1 for the saturation magnetiza-tion, 4~Ms, vertical remanence, Mr/MS and vertical coercivity Hc for vertical recording media for reported usage in the NRZ moàe and the workable parameters for the RZ vertical recording of tY~e present invention.
T~BLE I
Typical Mediu~ Characteristics Vertical Recording Media - -NRZ RZ
4~Ms2000-6000 4000-10000 Gauss ~ r/MS30-80 2-20 %
i~
Hc 600-1200 200-800 Oe `~ :
:~
The preferxed embocliment of the RZ vertical recording medium is shown in FIG. 4. The mediurn comprises a nonmagnetic substrate 32, a high permeability underlayer 34 and the low coercivity RZ
recording layer 36. The medium is DC erased prior to recordirg to produce the magnetization configuration shown by the arrows in the drawing (FIG. 4). When the RZ vertical recording magnetic -read/write head 14 is energized with a unidirec~ional current pulse (see FIG. 3a) a write field configuration is produced as shown in FIG. 5. This bipolar write field closes substantially ~5 perpendicular to the surface of the recording medium and s centered about the transducing gap 30 of the recording head 14 as shown by the centerline of s~mmetry 31. The resulting recorded transition is also centered ~bout the gap 30 as sho~.m in FIG. 6.
.
The recording method according to the invention utilizes vertical recording in a RZ mode. To produce recording in the RZ vertical `jrecording mode it is necessary to use a short pulse of wrile current instead of polarity reversals, as used in the prior art "non return to zero" NRZ recording mode. This is illustrated in ~, S~984009 4 ~2~;36~
\
FIG. 3b in which the NRZ write current is ON at some selected level I
all the time, and to write a transition, the polarity of the write current is reversed. As shown in FIG. 3b at time t=tO the write current is at +I, and at time t=tl, the polarity of the write current is switched to -I to write a first transition. At t=t2, the polarity of the write current is again switched to +I to write a second transition.
In contrast to this operation, FIG. 3a shows write current for the RZ
vertical recording mode at zero at time t=t0, and the write current remains at zero until time t=tl. At this time a short pulse of write current with pulse length T and amplitude I is produced to record a first transition. The write current then returns to zero until a second short pulse of write current, with pulse length T, is produced at time t=t2 to produce a second transition. The write current for the RZ
vertical recording mode is a short pulse of current, and the write process takes place symmetrically about the gap region of the head. The associated write field has bipolar symmetry and has a spatial extent directly governed by the pole piece geometry. In this context, bipolar describes a magne~ic field or magnetic flux centered about the transducing gap having on one side an excursion in the upward direction and on the other side a substantially equal excursion in the downward direction with respect to the plane of the recording medium. The data bits recorded in the recording medium 16 in response to the short pulses of current have a symmetric bipolar magnetization configuration~ and have their size limited by internal demagnetiz~ng fields.
The RZ vertical recording system embodying the invention has the advantages of not only lower write current but also of increased linear storage density. The resulting output signal is improved in both amplitude and wave form. In addition, since the vertical magnetization vanishes between data bits in the RZ vertical recording method according to the invention, a variety of options are available for data encoding.
To contrast the operation according to the RZ vertical recording according to the present invention, FIG. 4 provides a comparative overview of NRZ and RZ recording principles when used with horizontal and vertical rscording modes. For each of these modes, the table shows the write current and relative head/medium position for writing an isolated transition, the write field 36~l8 profile with the portion effecting the transition accentuated, the response of the magnetization at time t=tO, and the remanent magnetization after the head has passed.
Of the techniques shown in FIG. 4, NRZ horizontal and NRZ vertical are the conventional methods, and the RZ vertical method is the method of the present invention. The RZ horizontal method is not viable since there exists no demagnetizing effect to quench the remanent magnetization away from the transition.
For the RZ vertical recording method, it can be seen that a transition is produced which not only is symmetrical but also is sharper. The transition is sharper because the write field gradients below the gap are substantially larger than that gradient below the heads' trailing edge which is used with NRZ recording.
It has been shown that a short pulse of write current in the vertical recording mode produces advantageous operation when considering isolated data bits. Since the vertical magnetization vanishes between data bits in the RZ vertical recording method, some options are available for data encoding. Since it is desired to select an encoding option which produces the greatest recording density, these options will be considered.
There are three options for data encoding. A first option is with single polarity write pulses, in which data is encoded by the presence or absence of a pulse. A second option is with alternating polarity write pulses, in which data is encoded by having a positive or negative pulse. A third option allows for data encoding using ternary, bipolar write pulses, in which data is encoded by having no pulse, a positive pulse, or a negative pulse. The first two of these options are examined with the aid of FIG. 9, which analyzes a write sequence consisting of two pulses of alternating polarity (a) and alternatively, two single polarity (b) pulses. Pulse width is Tl. The spacing between pulses is T2. Time instances of interest labelled tl through t7. For each of these instances, the figure shows the corresponding head position, the write field profile (dashed curve), and the response of the magnetization. It is assumed that the medium has previously been DC
erased, leaving the small uniform remanent magnetization evident in the "tl". In the encoding method shown in FIG. 6, information is defined by the presence (1) or absence . ., ~536~13 ~, (0) of a pulse, but other encoding methods could be used. At t2, the flrst write pulse is applied, producing the depicted transition. While the pulse is one, this transition remains stationary relative to the wri~e field, propagating along the medium at the velocity, v. At t3, which marks the trailing edge of the pulse, the transition freezes in the medium, while, because of the demagnetizing fields, there occurs some slimming of the transition profile. The location of its formation has now moved a distance sl=vxTl from the recording head.
The second write pulse occurs at t4. Between t3 and t4 the bit moved a distance s2=vxT2. Let us find the minimum pulse spacing, T2, such that the write field of the second pulse does not affect the previously recorded bit. This minimum separation must depend on the spatial extent of the write field. For the sake of a simple argument, we assume that the effective write field extends just to the outer edge of the pole pieces and that the shoulders of a written magnetization profile have the same spatial extent. Then, at t5, the leading edge of the second write pulse, the head needs to be separated from the recorded bit at least by a distance: (single polarity) s2=(2p+g); (alternating polarity) s2=(p+g); where g and p are the length of the gap and the pole pieces, respectively. This minimum separation defines T2=s2/v, the min.
spacing between write pulses. By t6, the second transition freezes in the medium. The final illustration, at t7, shows both transitions recorded and moving with the medium.
From above, the minimum separation between adjacent data bits is:
s=vT+(2p+g), for the single polarity sequence, and s=vT+(lp+g), for the alternating polarity sequence In the RZ mode, the attainable recording density is limited by head geometry, medium velocity and duration of the write pulse, as shown in FIG. 10. This figure shows reciprocal bit spacing as a function of medium velocity for two different head geometries and two different pulse lengths. From FIG. 10 it can be seen that the attainable density is predominantly limited, at lower media velocities, by head geometry and, at higher media velocities, by the length of the write pulses.
. ..
In suitable systems, vertical recording in the RZ mode provides improvements in linear density as well as in the amplitude and ` ~253~
waveform of the output signal. In terms of the write process, the RZ
mode utilizes write field reductions which permit the use of much simplified write head configurations. With regard to the medium, the RZ
method opens up a new approach to the design of recording media.
Improvements in recording density do not have to rely on further increases of coercivity, but instead, are sought through a judicious choice of media characteristics.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.
Claims (15)
1. A vertical magnetic recording method comprising the steps of:
providing a magnetic recording medium having low vertical remanence;
positioning a magnetic transducer having means for producing a bipolar magnetic field and a recording gap so that said recording gap is in close proximity to said magnetic recording medium;
producing relative motion between said magnetic transducer and said magnetic recording medium; and energizing said means for producing a bipolar magnetic field with a unidirectional recording current impulse of short duration to write a bipolar recorded transition beneath said recording gap in said magnetic recording medium.
providing a magnetic recording medium having low vertical remanence;
positioning a magnetic transducer having means for producing a bipolar magnetic field and a recording gap so that said recording gap is in close proximity to said magnetic recording medium;
producing relative motion between said magnetic transducer and said magnetic recording medium; and energizing said means for producing a bipolar magnetic field with a unidirectional recording current impulse of short duration to write a bipolar recorded transition beneath said recording gap in said magnetic recording medium.
2. The vertical magnetic recording method according to claim 1 wherein said energizing step comprises energizing said means for producing a magnetic field with successive ones of said unidirectional current impulses produced in a mode in which impulses have the same polarity.
3. The vertical magnetic recording method according to claim 1 wherein said energizing step comprises energizing said means for producing a bipolar magnetic field with successive ones of said unidirectional current impulses produced in a mode in which said impulses alternate in polarity between a positive impulse and a negative impulse.
4. The vertical magnetic recording method according to claim 1 wherein said positioning step comprises positioning said magnetic transducer so that said recording gap is substantially in contact with said recording medium.
5. The vertical magnetic recording method according to claim 1 wherein said unidirectional current impulse has a duration which is short relative to the spacing between adjacent recorded transitions divided by said relative velocity between said magnetic transducer and said magnetic recording medium.
6. The vertical magnetic recording method according to claim 1 wherein said unidirectional current impulse has a duration not substantially greater than the length of the pole pieces forming said recording gap divided by the velocity of said relative motion of said magnetic recording medium.
7. The vertical magnetic recording method according to claim 1 wherein said magnetic recording medium has a vertical remanence of less than 20 percent.
8. A vertical magnetic recording system for recording magnetic field signals representing information on an associated recording medium, said system comprising a selectively magnetizable recording medium, at least one recording head, means for producing relative motion between the recording medium and the recording head, and means for supplying signals representing information to the recording head for recording upon the medium, the improvement comprising:
said recording medium having a recording layer of magnetic material thereon, said recording layer of magnetic material having low vertical remanence; and said means for supplying signals representing information supplying one unidirectional current impulse of short duration to said recording head for each unit of information to be recorded upon said recording medium wherein the direction of the magnetic recording field applied to said recording layer of said recording medium is substantially perpendicular to the surface of said recording medium such that the magnetic flux passes transversely through said recording layer whereby the magnetic recording is produced in the vertical recording mode.
said recording medium having a recording layer of magnetic material thereon, said recording layer of magnetic material having low vertical remanence; and said means for supplying signals representing information supplying one unidirectional current impulse of short duration to said recording head for each unit of information to be recorded upon said recording medium wherein the direction of the magnetic recording field applied to said recording layer of said recording medium is substantially perpendicular to the surface of said recording medium such that the magnetic flux passes transversely through said recording layer whereby the magnetic recording is produced in the vertical recording mode.
9. The vertical magnetic recording system according to claim 8 wherein successive ones of said unidirectional current impulses are produced in a mode in which impulses have the same polarity.
10. The vertical magnetic recording system according to claim 8 wherein successive ones of said unidirectional current impulses are produced in a mode in which impulses alternate in polarity between a positive impulse and a negative impulse.
11. The vertical magnetic recording system according to claim 8 wherein the recording head is positioned substantially in contact with the recording medium.
12. The vertical magnetic recording system according to claim 8 wherein said unidirectional current impulse has a duration which is short relative to the spacing between adjacent recorded transitions divided by said relative velocity between said recording head and said magnetic recording medium.
13. The vertical magnetic recording system according to claim 8 wherein said unidirectional current impulse has a duration not substantially greater than the length of the pole pieces of said recording head divided by the velocity of said relative motion between said recording medium and said recording head.
14. The vertical magnetic recording system according to claim 8 wherein said recording layer of magnetic material has a vertical remanence of less than 20 percent.
15. The vertical magnetic recording system according to claim 8 wherein said recording head produces a bipolar magnetic field.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000513651A CA1253618A (en) | 1986-07-11 | 1986-07-11 | Return-to-zero magnetic recording system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000513651A CA1253618A (en) | 1986-07-11 | 1986-07-11 | Return-to-zero magnetic recording system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1253618A true CA1253618A (en) | 1989-05-02 |
Family
ID=4133554
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000513651A Expired CA1253618A (en) | 1986-07-11 | 1986-07-11 | Return-to-zero magnetic recording system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1253618A (en) |
-
1986
- 1986-07-11 CA CA000513651A patent/CA1253618A/en not_active Expired
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