Patent Application
20110171494
The present invention relates to a ferromagnetic recording film with perpendicular magnetic anisotropy, and more particularly to a discontinuous islanded ferromagnetic recording film with perpendicular magnetic anisotropy.
The recording density of the magnetic recording medium is inversely proportional to the size of the magnetic particle. According to the Stoner-Wohlfarth model, the minimum thermal stable grain size (Dp) of a magnetic recording medium is (60 KBT/Ku)1/3, wherein Ku is the magnetocrystalline anisotropy constant, KB is the Boltzmann constant and T is the absolute temperature. Currently, the material of the most commonly used recording medium for the hard disk is the CoCrPtM alloy film (M=B, Ni, Ta or W), whose Ku is about 2×106 erg/cm3. Therefore, when the size of the magnetic particle of the CoCrPtM alloy film is smaller than 10 nm, the thermal stability will be deteriorated. Patterned media have been suggested as a potential solution for this physical limit.
L10 FePt film is the most promising candidate for application in magnetic recording media to increase the recording density beyond 1 Tb/in2, because its high magnetocrystalline anisotropy constant (Ku˜7×107 erg/cm3) could delay the occurrence of the superparamagnetic effect to reduce remarkably the minimal stable grain size to 3 nm. Hence, the FePt alloy film is promising to replace the current CoCrPt alloy film to become the mainstream material of the ultrahigh density magnetic recording medium in the next generation. In order to use FePt films as a patterned media, the well-separated L 10 FePt nano-size islands onto Pt, Cr or Ru underlayer and a suitable porous anodic alumina (PAA) pattern plate had been widely studied. But these multilayer films result in the higher cost, poor reproducibility and undesirable interdiffusions between the FePt magnetic layer and underlayers.
The laser interference lithography (LIL), focused ion beam (FIB) and electron beam lithography methods have previously been investigated to fabricate the patterned magnetic thin films. However, these processed are not practical for the industrial production because their manufactures are prohibitively slow and expensive.
In order to overcome the drawbacks in the prior art, a well-separated and discontinuous islanded ferromagnetic recording film with perpendicular magnetic anisotropy is provided. The particular design in the present invention not only solves the problems described above, but also is easy to be implemented. Thus, the present invention has the utility for the industry.
In accordance with one aspect of the present invention, a discontinuous islanded ferromagnetic recording film with perpendicular magnetic anisotropy is provided. The discontinuous islanded ferromagnetic recording film includes a substrate; and a ferromagnetic layer formed on the substrate; wherein a surface energy difference existed between the ferromagnetic layer and the substrate turns the ferromagnetic layer into well-separated and discontinuous islanded ferromagnetic particles after performing a high-temperature vacuum annealing process, each discontinuous islanded ferromagnetic particle is thought of a single magnetic domain, so as to obtain the discontinuous islanded ferromagnetic recording film with perpendicular magnetic anisotropy.
Preferably, the substrate is amorphous.
Preferably, the substrate is made of a glass substance.
Preferably, a surface energy of the ferromagnetic layer is larger than the substrate.
Preferably, the ferromagnetic layer is made of a Fe-based alloy film.
Preferably, the Fe-based alloy film is a multilayer (Fe/Pt) alloy film.
Preferably, the ferromagnetic layer is formed on the substrate by a magnetron sputtering.
Preferably, a film thickness of the ferromagnetic layer is below 5 nm.
Preferably, the high-temperature vacuum annealing process is performed for the ferromagnetic layer at a temperature range of 600˜800° C. for 5˜15 minutes with a vacuum range of 1˜10 mTorr.
Preferably, the high-temperature vacuum annealing process is performed under a protection gas of argon (Ar).
Preferably, the surface energy difference is in a range of 1500˜2500 erg/cm2.
Preferably, a diameter of the discontinuous islanded ferromagnetic particle is in a range of 2.5˜5 nm.
Preferably, an out-of-plane coercivity of the discontinuous islanded ferromagnetic recording film is larger than 20000 Oe.
Preferably, a saturation magnetization of the discontinuous islanded ferromagnetic recording film is larger than 400 emu/cm3.
Preferably, an out-of-plane squareness of the discontinuous islanded ferromagnetic recording film is larger than 0.7.
Preferably, a density of the discontinuous islanded ferromagnetic particles on the substrate is larger than 1.5×1013 islands/inch2.
The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed descriptions and accompanying drawings, in which:
The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for the purposes of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed.
The present invention provides a well-separated and discontinuous islanded ferromagnetic recording film with perpendicular magnetic anisotropy. The well-separated and discontinuous islanded ferromagnetic recording film includes a substrate and a ferromagnetic layer. The substrate is one of a glass substrate or a substrate having a surface energy which is smaller than the ferromagnetic layer, and the structure of the substrate is amorphous. The ferromagnetic layer is formed on the substrate by a direct current magnetron sputtering. The ferromagnetic layer is a Fe-based alloy film, preferably a multilayer (Fe/Pt) alloy film with a film thickness below 5 nm. A high-temperature vacuum annealing process is performed for the as-deposited multilayer (Fe/Pt) alloy film at a temperature of 700° C. for 10 minutes with a vacuum of 1 mTorr, wherein the high-temperature vacuum annealing process is performed under the protection gas of argon (Ar). The multilayer (Fe/Pt) alloy film could reduce the diffusion length of Fe atoms and Pt atoms for ordering transformation and promote the ordering face-centered tetragonal (FCT) L10 FePt(001) texture formation. A surface energy difference existed between the multilayer (Fe/Pt) alloy film and the substrate turns the multilayer (Fe/Pt) alloy film into well-separated and discontinuous islanded ferromagnetic particles after performing the high-temperature vacuum annealing process. An out-of-plane coercivity (Hc⊥) of the discontinuous islanded ferromagnetic recording film is larger than 20000 Oe after performing the high-temperature vacuum annealing process, which reveals a significant potential as the perpendicular magnetic recording media for ultra high-density recording.
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The magnetic properties of the multilayer (Fe/Pt) alloy film of the present invention is measured by the superconducting quantum interference device (SQUID) and vibrating sample magnetometer (VSM), and the microstructure thereof is observed by the field emission gun transmission electron microscope (FEG-TEM).
The as-deposited 1 nm multilayer (Fe/Pt) alloy film is annealed in a high-temperature vacuum annealing furnace with the protection gas of Ar at 700° C. for 10 minutes with a vacuum of 1 mTorr and then water cooled.
The as-deposited 1 nm multilayer (Fe/Pt) alloy film is annealed in a high-temperature vacuum annealing furnace with the protection gas of Ar at 700° C. for 30 minutes with a vacuum of 1 mTorr and then water cooled.
The as-deposited 5 nm multilayer (Fe/Pt) alloy film is annealed in a high-temperature vacuum annealing furnace with the protection gas of Ar at 700° C. for 30 minutes with a vacuum of 1 mTorr and then water cooled.
The as-deposited 15 nm multilayer (Fe/Pt) alloy film is annealed in a high-temperature vacuum annealing furnace with the protection gas of Ar at 700° C. for 30 minutes with a vacuum of 1 mTorr and then water cooled.
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According to the present invention, a well-separated and discontinuous islanded ferromagnetic recording film with perpendicular magnetic anisotropy could be achieved by a high-temperature vacuum annealing process at a temperature of 700° C. for 10 minutes with a vacuum of mTorr. The out-of-plane coercivity, saturation magnetization and out-of-plane squareness of the 1 nm multilayer (Fe/Pt) alloy film annealed at 700° C. for 10 minutes are larger than 20000 Oe, 400 emu/cm3 and 0.7, respectively. The diameter of the discontinuous islanded ferromagnetic particle is in a range of 2.5˜5 nm, and the density of the discontinuous islanded ferromagnetic particles on the substrate is larger than 1.5×1013 islands/inch2. Besides, the domain structure of the 1 nm multilayer (Fe/Pt) alloy film annealed at 700° C. for 10 minutes tends to isolated magnetic domains, and each discontinuous islanded ferromagnetic particle is thought of a single magnetic domain. Therefore, the 1 nm multilayer (Fe/Pt) alloy film annealed at 700° C. for 10 minutes would be a great benefit to increase the recording density and reduces the media noise of the magnetic film, which reveals the prominent candidate to be applied for the perpendicular magnetic recording media.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 099100333 | Jan 2010 | TW | national |
