Coating processes – Magnetic base or coating – Magnetic coating
Reexamination Certificate
2002-06-25
2003-09-23
Pianalto, Bernard (Department: 1762)
Coating processes
Magnetic base or coating
Magnetic coating
C427S131000, C427S132000, C427S380000, C427S383100, C427S404000
Reexamination Certificate
active
06623789
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for fabricating a magnetic recording medium.
2. Description of the Prior Art
With the development of IT technology, high density recording technique is desired in order to record a large amount of information. Particularly, in the magnetic recording field where a large amount of information must be recorded with high precision, a high performance medium is strongly desired.
As of now, Co—Cr based alloy is utilized for such a high density recordable medium. In such a Co—Cr based alloy, ferromagnetic fine particles made of Co—Cr based alloy containing Co as main composition are precipitated in a matrix of non-magnetic Co—Cr based alloy containing Cr as main composition. In this case, one recording unit defined as one bit is composed of an assembly of the fine particles, and then, reduction of recording noise is realized by clear boundary between the adjacent bits and the recording resolution an be improved.
In order to achieve high density recording, however, it is required that the size of each particle made of Co—Cr based ferromagnetic alloy is reduced to obtain high resolution and low recording noise. It is also required that the magnetic intersection between the particles is removed.
If the size of each Co—Cr based ferromagnetic particle is reduced down to 10-20 nm, the thermal agitation to each particle becomes larger than the magnetic energy so that the ferromagnetic property is diminished, which is called as “super paramagnetism phenomena”. In this point of view, attempts to seek for research and develop a new high anisotropy magnetic material in place of the Co—Cr based alloy have been made.
As a result, (Fe, Co, Ni)—(Pt, Pd) alloy was developed as a high anisotropy magnetic material. The alloy has a magnetic anisotropy energy about tenfold as large as that of the Co—Cr alloy as mentioned above if the alloy has an ordered phase (L1
0
phase). In order to obtain (Fe, Co, Ni)—(Pt, Pd) films of ordered phase, the alloy is deposited on a substrate by vacuum deposition or sputtering, and thereafter, thermally treated at 600-700° C.
In such a high temperature thermal treatment, however, the crystal gains of the (Fe, Co, Ni)—(Pt, Pd) alloy grow and increase in size, so that the high density recording media can not be realized even by utilizing the (Fe, Co, Ni)—(Pt, Pd) alloy. Moreover, the substrate on which the alloy is deposited is thermally deformed, causing many obstacles in the subsequent fabrication process.
SUMMERY OF THE INVENTION
It is an object of the present invention to provide a new high density magnetic recording medium.
In achieving the above object, this invention relates to a method to fabricate a magnetic recording medium, comprising the steps of:
preparing a first thin film layer including at least one transition metal selected from the group consisting of Co, Fe and Ni, and a second thin film layer including at least one platinum group element selected from the group consisting of Pt and Pd,
forming a multilayered structure where the first thin film layer and the second thin film layer as stacked, and
heating the multilayered structure at the same time or after formation of the multilayered structure, thereby inducing inter-diffusion of the first and the second thin film resulting in an alloy layer including the at least one transition metal and the at least one platinum group element.
The inventors had intensely studied to develop a new magnetic high density recording medium. They paid much attention to the (Fe, Co, Ni)—(Pt, Pd) alloy, and made a number of attempts to synthesize its ordered phase of at lower temperature.
As a result, the inventors developed out the following means. First of all, a (Fe, Co, Ni) layer and a (Pt, Pd) layer are formed independently. Then, this multilayered structure is heated at a given temperature so that Fe, Co and/or Ni in the (Fe, Co, Ni) layer and Pt and/or Pd in the (Pt, Pd) layer are inter-diffused. In this case, the inter-diffusion is performed at a very low temperature of 300-500° C.
Furthermore, they found that, since ordering of the phase is provoked at low temperature as described above, growth of (Fe, Co, Ni) crystal grains is suppressed in the inter-diffusion process resulting in the fine particle structure with the grain size as small as 10-20 nm. This invention was made based on these experimental results.
According to the invention the ambient temperature for alloying of (Fe, Co, Ni) and (Pt, Pd) and ordering is reduced appreciably. Moreover, this low temperature leads to suppression of grain growth resulting in very fine ordered (Fe, Co, Ni) particles. Another advantage is that the substrate temperature for formation and ordering of the alloy can be reduced and the problem of thermal damage is removed making the process coming afterwards easier.
In a preferred embodiment of the present invention, the first layer is of a granular structure including a transition metal and the second layer is of a granular structure including a platinum group element.
In another preferred embodiment of the present invention, the first layer is of a granular structure made of a transition metal alloy that includes at least one transition element and the second layer is a platinum group alloy that includes at least one platinum group element.
In the another preferred embodiment of the present invention, the first layer is of a transition metal alloy that includes at least one transition element and the second layer is of a granular structure made of a platinum group alloy that includes at least one platinum group element.
As mentioned above, in the preferred embodiment of the present invention, at least one of the two layers, one of which is made of at least one element selected from transition group of Fe, Co and N, and another of which is made of at least on element selected from platinum group of Pt and Pd, is of a granular structure.
Therefore, the alloying is performed maintaining this granular structure making easier the process of ordering and formation of (Fe, Co, Ni) fine particle assembly,
In the other preferred embodiment of the invention, Ag is used as a matrix for the granular structure in either the first or the second granular layer. In this case, the ordering temperature is reduced more, namely, 200-400° C.
In the other preferred embodiment of the invention, Ag particles are added to the granular structure in either the first or the second granular layer. In this case, the ordering temperature is reduced more, namely, 200-400° C.
The term [granular] collectively means a structure composed of a matrix of oxide, nitride or fluoride and the particles depressed in them. Subsequently, in the recording medium produced according to the present invention the ordered alloy particles of (Fe, Co, Ni) are dispersed in the matrix mentioned above.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention will be described in detail. In the case that the first layer is a transition metal granular structure containing at least one of Co, Fe and Ni, and the second layer is a platinum group granular structure containing at least one of Pt and Pd, according to the preferred embodiment of the present invention, the thickness of the transition metal granular layer is preferably set within 1.0-20 nm, particularly within 2.5-5.0 nm.
Similarly, the thickness of the platinum group granular layer is preferably set within 1.0-20 nm, particularly within 2.5-5.0 nm. In this case, the sizes of the (Fe, Co, Ni)—(Pt, Pd) alloy particles can be reduced when the (Fe, Co, Ni)—(Pt, Pd) alloy particles are made by fabricated utilizing the inter-diffusion of the between the first and the second layers. Moreover, the coercive force of the resulting magnetic recording medium composed of the (Fe, Co, Ni)—(Pt, Pd) alloy particles can be enhanced sufficiently, and recorded data can be maintained stably for a long period of time.
The content of the transition metal fine particles in the transition metal granular layer is preferably set within 20-90 atomic percen
Kitakami Osamu
Okamoto Satoshi
Sakurai Tomoaki
Shimada Yutaka
Pianalto Bernard
Tohoku University
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