Dynamic magnetic information storage or retrieval – General recording or reproducing – Thermomagnetic recording or transducers
Reexamination Certificate
2000-01-07
2003-08-05
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Thermomagnetic recording or transducers
C360S066000, C428S690000
Reexamination Certificate
active
06603619
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic storage media for magnetically recording and reproducing information in a recording domain by heating the domain to a high temperature using a heat source, and also to heat assisted recording and reproduction methods applied to such media.
BACKGROUND OF THE INVENTION
Heat assisted magnetic recording and reproduction schemes have recently been developed to realize high density storage as a fusion of optical technology and magnetic recording and reproduction technology. Japanese Laid-Open Patent Application No. 4-176034/1992 (Tokukaihei 4-176034, corresponding to U.S. Pat. No. 5,656,385 dated Aug. 12, 1997), for example, discloses a magnetic storage medium made of a ferromagnetic material having a compensation temperature set substantially to room temperature, as well as a heat assisted magnetic recording and reproduction scheme using laser light for such a medium.
In the heat assisted magnetic recording and reproduction scheme, information is recorded in a recording domain of a magnetic storage medium by applying an external magnetic field from a recording magnetic head while heating the recording domain to a high temperature using laser light to reduce the coercive force of the recording domain. Meanwhile, according to the scheme, information is reproduced by, again, heating the recording domain to a high temperature with laser light to amplify the strength of residual magnetization in the recording domain, and detecting the magnetic flux generated by the residual magnetization using a reproduction magnetic head.
In the foregoing scheme, the domains where temperature remains at room temperature without being elevated to high temperatures with laser light, have residual magnetization that is ignorably small. Therefore,the crosstalk from adjacent tracks can be restrained to substantially low levels even with a gap width, i.e., a width of the reproduction magnetic head measured perpendicular to the track direction, that is larger than the pitch of the track where information is stored, enabling reproduction of information from a high density storage medium.
Meanwhile, Japanese Laid-Open Patent Application No. 4-95201/1992 (Tokukaihei 4-95201, corresponding to Japanese Patent 2636957, Date of Patent Apr. 25, 1997) discloses a heat assisted magnetic reproduction method whereby signals from adjacent tracks are reduced to restrain crosstalk by heating both sides of the track to be reproduced to high temperatures using a light beam so as to elevate the temperature thereof to a neighborhood of the magnetic compensation temperature at which the residual magnetization is zero.
According to conventionally suggested heat assisted reproduction methods, information is retrieved either by amplifying magnetization by way of heating a reproduction domain or by reducing magnetization to restrain crosstalk by way of heating a neighborhood of a reproduction domain.
Therefore, heat works on only limited areas: either a reproduction track domain or two adjacent tracks of a reproduction track. Either way, information is reproduced using difference in the strength of residual magnetization between domains where temperature is elevated and where temperature is not elevated.
The magnetic compensation temperature of a ferrimagnetic material storage medium is highly susceptible to the composition of the storage medium; a small variation in the composition causes a great change in the magnetic compensation temperature.
For example, an experiment conducted by the inventors of the present invention on a magnetic film of a TbFeCo alloy showed that a fluctuation as small as a few percentage points in the composition ratio of the Tb and the FeCo causes the magnetic compensation temperature to change a few dozen degrees centigrade.
FIG. 26
shows the dependency on the composition ratio, wherein the composition ratio of Tb and FeCo is plotted along the axis of ordinates and the magnetic compensation temperature (referred to as compensation temperature in the figure) is plotted along the axis of abscissas. In this example, a 1% change in the composition ratio caused a 20° C. change in the magnetic compensation temperature.
Consequently, irregularities in the manufacturing process of magnetic storage media constitute an obstacle in the precise setting of the magnetic compensation temperature. Further, considering the actual operational conditions for the recording and reproduction system, since ambient temperature supposedly differs wildly depending on operational environment, the foregoing heat assisted reproduction has trouble in the accurate setting of temperature in the non-elevated temperature domain of the storage medium.
As described in the foregoing, the conventionally suggested heat assisted recording and reproduction has following problems: (1) It is difficult to precisely specify the magnetic compensation temperature of the storage medium and the temperature of the non-elevated temperature domain; (2) Occurrence of crosstalk is inevitable, and (3) Stability in recording and reproduction is low.
SUMMARY OF THE INVENTION
With the foregoing problems taken into consideration, the present invention has an object to offer a heat assisted recording and reproduction method that is stable against, and is hardly affected by, irregularities in the magnetic compensation temperature that occur in the manufacturing process of a magnetic storage medium due to irregularities in the composition, and variations in the temperature of the storage medium caused by ambient temperature at the magnetic storage medium operates.
The present invention has another object to offer a magnetic storage medium used together with a heat source, such as a head employing magneto-resistance effect, as well as to offer a heat assisted recording and reproduction method applied to such a magnetic storage medium, the magnetic storage medium being suited to reproduce information stored in high density with crosstalk occurring due to irregularities in the temperature of the medium only in a restrained manner and hence being capable of producing a good S/N ratio, even if a heat assisted magnetic recording and reproduction method is applied.
To solve the foregoing problems, a magnetic storage medium of the present invention includes a storage layer for use in heat assisted recording and reproduction whereby information is magnetically recorded and reproduced by heating a recording domain, wherein saturated magnetization of the storage layer has a maximum value at a temperature between a magnetic compensation temperature and a Curie point, the temperature being specified in a range from 150° C. to 250° C., and the magnetic compensation temperature of the storage layer is specified higher than room temperature.
In the arrangement, in the magnetic storage medium, the temperature at which the saturated magnetization of the storage layer takes its maximum value between the magnetic compensation temperature and the Curie point is specified in a range from 150° C. to 250° C.; therefore, in the recording domain heated to a neighborhood of the temperature at which the saturated magnetization takes its maximum value, the residual magnetization of the recording domain can be increased, and the information can be reproduced satisfactorily from the recording domain of the storage layer.
Here, for example, even if the head acts as a heat source causing the ambient temperature of the storage layer to exceed room temperature, such as in a case where a head exhibiting a magneto-resistance effect is used for reproduction, since the magnetic compensation temperature of the storage layer can be specified according to the ambient temperature that is higher than room temperature, the temperatures of the recording domains, except that of a recording domain heated for the purpose of reproduction, are equal to the ambient temperature, i.e., equal to the magnetic compensation temperature, and the magnetization is substantially zero. As a result, in the medium, the recording domain to be reproduced is protecte
Katayama Hiroyuki
Kojima Kunio
Ogimoto Yasushi
Sawamura Shinzo
Conlin David G.
Edwards & Angell LLP
Holder Regina N.
Tucker David A.
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