Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
2000-11-13
2004-03-02
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C427S127000, C427S129000, C427S130000, C427S552000, C252S062560, C252S062570, C252S062630
Reexamination Certificate
active
06699332
ABSTRACT:
This application claims priority to Singapore patent application No. 200003966-9 filed Jul. 17,2000, entitled METHOD OF PRODUCING A MAGNETIC RECORDING MEDIUM, which is hereby incorporated by reference.
The present invention relates to a method of converting a non-magnetic material into a magnetic state by annealing, and to a method of producing a magnetic recording medium such as a hard disk, particularly a patterned magnetic nanostructured medium for magnetic recording applications.
Conventionally, a magnetic recording medium for a hard disk is produced by sputter depositing a Co-alloy thin film on a chromium-based underlayer, as disclosed for example in U.S. Pat. No. 5,693,426.
The term “underlayer” refers to a layer of thin film, which Is deposited below the magnetic layer of a recording medium. The purpose of an underlayer is to provide favourable crystalline growth conditions for the magnetic layer and to achieve many useful recording properties. In the current magnetic recording materials, the underlayers are made of NiAI layer and a Cr Layer.
However, the magnetization vectors written on such disks lie in the plane of the film and are not stable at higher recording densities. Therefore, the current media are not expected to support densities higher than 300 Gb/in
2
. Different alternatives such as perpendicular magnetic recording (in which the magnetization of the written bits lie perpendicular to the film and is more stable), or patterned structures of magnetic islands are sought for future high-density recording media.
A schematic view of a patterned media for a ultrahigh density of the order of 1000 Gb/in
2
is shown in
FIG. 1. A
substrate is provided comprising a layer of a non-magnetic material that can be converted into a magnetic state, and selected portions of the non-magnetic layer are converted into a magnetic state to produce an array of magnetic “islands” in a non-magnetic matrix.
Techniques such as electron beam lithography and laser interferometry have been employed for producing such magnetic islands. Nanostructures have also been fabricated using an atomic force microscope or a scanning tunneling microscope. However, these methods have not been suitable for mass production. With electron beam lithography, a number of processing steps are typically involved and the production rate is slow, and laser interferometry can be an impractical method when forming patterns over a wide area or on a circular disk.
It is an aim of the present invention to provide an alternative method for converting a non-magnetic material into its magnetic state, particularly in the production of a patterned magnetic recording medium.
According to a first aspect of the present invention, there is provided a method of converting a material into a magnetic state by annealing, wherein the annealing is carried out by directing a focussed beam of radiation onto the material.
According to a second aspect of the present invention, there is provided a method of producing a magnetic recording medium comprising the steps of providing a substrate having a layer of a non-magnetic material that can be converted into a magnetic state by annealing, and then converting selected portions of the non-magnetic layer to a magnetic state by subjecting them to annealing by directing a focussed beam of radiation onto the substrate to form a patterned magnetic layer comprising an ordered array of magnetic regions separated by non-magnetic regions.
The term “magnetic state” refers to state which exhibits ferromagnetism or ferrimagnetism, preferably at normal temperatures.
Examples of materials which are non-magnetic (i.e., they do not possess magnetization in a zero magnetic field) in the as-deposited state, and require high temperature annealing (typically 800° C.) to obtain the necessary crystalline structure in which the films become ferromagnetic or ferrimagnetic are Ba-ferrite, Sr-ferrite, Co-ferrite, garnets and CrPt
3
. Co. Co—Zn ferrites and Fe/Zr multilayer material undergo this transition at a lower temperature of 400° C. This class of materials are referred to as potentially magnetic materials.
Films of these materials have been annealed by subjecting the whole disk to heating at the required temperature such that the whole film becomes magnetic. However, disks prepared in this way have not yet been used for commercial production because they suffer from disadvantages such as relatively large grain size and relatively large noise.
With the method for producing a magnetic recording medium according to the present invention, the potentially magnetic material is locally heated using a focussed beam of radiation such as an electron beam or ion beam. Only the portion of the material exposed to the focussed beam of radiation undergoes a transformation of the crystal structure and is converted into the magnetic state. In this way, a tiny magnetic dot in a non-magnetic matrix can be obtained. By scanning pulses of the focussed beam of radiation over a layer of potentially magnetic material, an array of magnetic islands spread in a non-magnetic matrix can be produced.
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Piramanayagam Seidikkurippu N.
Wang Jian Ping
Crowell & Moring LLP
Data Storage Institute
Sheehan John
LandOfFree
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