This application claims priority of Taiwanese application No. 098132055, filed on Sep. 23, 2009.
1. Field of the Invention
This invention relates to a method for forming an ordered alloy, more particularly to a method involving forming layers of a first metal and layers of a second metal alternately disposed with the layers of the first metal under an elevated temperature.
2. Description of the Related Art
In the magnetic recording technology, perpendicular magnetic recording (PMR) materials have been successfully developed to achieve a high recording density. It is known in the art that FePt alloy having an ordered phase (or L10 phase), i.e., a face-centered tetragonal (FCT) crystal structure, exhibits a high magnetocrystalline anisotropy (MCA) and thus can be used in a PMR medium to enhance the thermal stability of the PMR medium. In addition, the ordered FePT alloy has an out-of-plane coercive field (Hc⊥) and an out-of-plane squareness (S⊥) higher than the requirements of a satisfactory PMR medium, which are respectively required to be higher than 1.0 kOe and 0.5. FePt alloy films used in the PMR medium are usually formed by sputtering techniques. The FePt alloy films thus formed normally have a disordered phase, i.e., a face-centered cubic (FCC) structure. Conventionally, the disordered FePt alloy is required to be annealed under a temperature of above 400° C. so as to be transformed from the FCC structure into the FCT structure and to be used in the PMR medium. However, the annealing temperature is too high and can result in problems, such as damage to semiconductor components to which the PMR medium is integrated, and an increase in the capital cost for making the PMR medium.
Therefore, the object of the present invention is to provide a method for forming an ordered alloy that can overcome the aforesaid drawback of the prior art.
According to this invention, there is provided a method for forming an ordered alloy that comprises: (a) forming a layer of a first metal with a layer thickness of less than 0.3 nm over a substrate; (b) forming a layer of a second metal with a layer thickness of less than 0.3 nm on the layer of the first metal under an elevated temperature sufficient to cause interdiffusion of atoms of the first and second metals between the layer of the first metal and the layer of the second metal so as to form the ordered alloy; and (c) repeating steps (a) and (b) until a predetermined layer thickness of the ordered alloy is achieved.
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which:
Referring to
Preferably, the layer thickness of each of the layers 331 of the first metal and the layers 332 of the second metal is greater than 0.01 nm and less than 0.3 nm.
Preferably, the first metal is Fe, Co, Ni, Mn, Au, or Cu, and the second metal is Pt, Pd, Cr, Al, or Cu with the proviso that the first metal and the second metal cannot be Cu at the same time. More preferably, the first metal is Fe, Co, or Ni, and the second metal is Pt, Pd, or Cr.
Preferably, formation of the ordered alloy 33 is performed by sputtering techniques.
Referring to
When the first metal and the second metal are respectively Fe and Pt, the following conditions are preferable: the elevated temperature ranges from 300° C. to 350° C., the carrier 43 has a rotation speed ranging from 1 rpm to 20 rpm during the sputtering, and the sputtering is conducted by applying an output power ranging from 20 W to 70 W to the target 41 of the first metal (Fe) and an output power ranging from 10 W to 36 W to the target 42 of the second metal (Pt). When the elevated temperature is 350° C., the following conditions are more preferable: the carrier 43 has a rotation speed ranging from 10 rpm to 20 rpm during the sputtering, and the layer thickness of each of the layers 331 of the first metal (Fe) and the layers 332 of the second metal (Pt) ranges from 0.014 nm to 0.12 nm.
When the output power applied to each of the targets 41, 42 is increased, the deposition rate of each of the layers 331, 332 is increased correspondingly. In addition, when the rotation speed of the carrier 43 is increased, the layer thickness of each of the layers 331, 332 is decreased correspondingly due to a shorter time period for the substrate 3 to stay at the first and second positions. Hence, the layer thickness of each of the layers 331, 332 can be controlled by adjusting the rotation speed of the carrier 43 and/or the output power applied to the targets 41, 42.
The following examples and comparative example are provided to illustrate the merits of the preferred embodiments of the invention, and should not be construed as limiting the scope of the invention.
A substrate 3 made from glass and having a size of 7 cm×7 cm was placed in a sputtering chamber. The substrate 3 was deposited with a first interlayer 31 of CrRu alloy with a layer thickness of 90 nm thereon under a working pressure of 5 mTorr and a substrate temperature of 300° C. A second interlayer 32 made from Pt and having a layer thickness of 2 nm was then formed on the first interlayer 31 by sputtering under a working pressure of 10 mTorr and a substrate temperature of 350° C. The substrate 3 formed with the first and second interlayers 31, 32 thereon was then mounted to a rotatable carrier 43 (which is in the form of a disc with a diameter of 50 cm) in a magnetron sputtering chamber 4 with targets of Fe and Pt (which have a size approximate to the size of the substrate 3) mounted diametrically therein. Sputtering was performed by applying an output power of 20 W to the target 41 of Fe and an output power of 10 W to the target 42 of Pt under an elevated temperature (i.e., annealing temperature) of 300° C. and a working pressure of 10 mTorr. The carrier 43 was operated at a rotation speed of 10 rpm to move the substrate 3 to the first and second positions alternately during sputtering. After sputtering, a total layer thickness of 20 nm of a FePt alloy 33 was obtained. The layer thickness of each of the layers 331 of Fe and the layers 332 of Pt of the FePt alloy was calculated based on the total layer thickness and the rotation speed of the carrier 43, and is shown in Table 1. The FePt alloy thus formed has a composition of Fe48Pt52 as determined by using energy dispersive spectrometry (EDS).
A FePt alloy of Example 2 (E2) was prepared by steps and operating conditions similar to those of Example 1 (E1), except that the rotation speed of the carrier 43 was 5 rpm, and the elevated temperature was 350° C. Each of the layers 331 of Fe and the layers 332 of Pt thus formed has a layer thickness of 0.0578 nm (see Table 1). The FePt alloy thus formed has a composition of Fe48Pt52.
A FePt alloy of Example 3 (E3) was prepared by steps and operating conditions similar to those of Example 2 (E2), except that the rotation speed of the carrier 43 was 20 rpm. Each of the layers 331 of Fe and the layers 332 of Pt thus formed has a layer thickness of 0.0145 nm (see Table 1). The FePt alloy thus formed has a composition of Fe48Pt52.
A FePt alloy of Example 4 (E4) was prepared by steps and operating conditions similar to those of Example 1 (E1), except that the elevated temperature was 350° C. Each of the layers 331 of Fe and the layers 332 of Pt thus formed has a layer thickness of 0.0289 nm (see Table 1). The FePt alloy thus formed has a composition of Fe48Pt52.
A FePt alloy of Example 5 (E5) was prepared by steps and operating conditions similar to those of Example 4 (E4), except that the output powers applied to the target 41 of Fe and target 42 of Pt were 40 W and 20 W, respectively. Each of the layers 331 of Fe and the layers 332 of Pt thus formed has a layer thickness of 0.0589 nm (see Table 1). The FePt alloy thus formed has a composition of Fe48Pt52.
A FePt alloy of Example 6 (E6) was prepared by steps and operating conditions similar to those of Example 4 (E4), except that the output powers applied to the target 41 of Fe and target 42 of Pt were 50 W and 25 W, respectively. Each of the layers 331 of Fe and the layers 332 of Pt thus formed has a layer thickness of 0.0749 nm (see Table 1). The FePt alloy thus formed has a composition of Fe48Pt52.
A FePt alloy of Example 7 (E7) was prepared by steps and operating conditions similar to those of Example 4 (E4), except that the output powers applied to the target 41 of Fe and target 42 of Pt were 60 W and 31 W, respectively. Each of the layers 331 of Fe and the layers 332 of Pt thus formed has a layer thickness of 0.0938 nm (see Table 1). The FePt alloy thus formed has a composition of Fe48Pt52.
A FePt alloy of Example 8 (E8) was prepared by steps and operating conditions similar to those of Example 4 (E4), except that the output powers applied to the target 41 of Fe and target 42 of Pt were 70 W and 36 W, respectively. Each of the layers 331 of Fe and the layers 332 of Pt thus formed has a layer thickness of 0.1113 nm (see Table 1). The FePt alloy thus formed has a composition of Fe48Pt52.
A FePt alloy of Example 9 (E9) was prepared by steps and operating conditions similar to those of Example 4 (E4), except that the rotation speed of the carrier 43 was 1 rpm. Each of the layers 331 of Fe and the layers 332 of Pt thus formed has a layer thickness of 0.289 nm (see Table 1). The FePt alloy thus formed has a composition of Fe48Pt52.
A FePt alloy of the comparative example was prepared by steps and operating conditions similar to those of Example 9 (E9), except that the output powers applied to the target 41 of Fe and target 42 of Pt were 40 W and 20 W, respectively. Each of the layers 331 of Fe and the layers 332 of Pt thus formed has a layer thickness of 0.5895 nm (see Table 1).
The relationship between the applied magnetic field (Ha) and magnetization (M), i.e., hysteresis-loops, of the FePt alloy of each of Examples (E1˜E9) and the comparative example (CE) was measured using a vibrating sample magnetometer (VSM).
From the hysteresis-loop shown in
The XRD plot shown in
From the hysteresis-loop shown in
From the hysteresis-loop shown in
From the hysteresis-loop shown in
From the hysteresis-loop shown in
From the hysteresis-loop shown in
From the hysteresis-loop shown in
From the hysteresis-loop shown in
The XRD curves shown in
From the hysteresis-loop shown in
From the hysteresis-loop shown in
1layer thickness of each layer of Fe and Pt
2rotation speed of the carrier
3elevated temperature of the sputtering operation
In conclusion, by forming alternately each layer of Pt with the layer thickness of less than 0.3 nm and each layer of Fe with the layer thickness of less than 0.3 nm, the annealing temperature in the method of this invention for forming the ordered alloy can be reduced to below 400° C. so that the aforesaid drawback of requiring a high annealing temperature for forming an ordered alloy in the prior art can be eliminated. Moreover, the ordered alloy thus obtained exhibits satisfactory and good Hc⊥ and S⊥ properties.
While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent arrangements.
Number | Date | Country | Kind |
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098132055 | Sep 2009 | TW | national |