Obviousness

The obviousness analysis under 35 U.S.C. § 103 requires determining whether the claimed invention would have been obvious to a person having ordinary skill in the art at the time the invention was made. This involves several factual inquiries: determining the scope and content of the prior art, ascertaining the differences between the claimed invention and the prior art, and resolving the level of ordinary skill in the pertinent art. A combination of prior art references can render a claim obvious if there was a motivation to combine them, even if that motivation is not explicitly stated in the prior art.

The priority date for US patent 11138997 is June 17, 2006. Therefore, the prior art for this analysis must predate this date. The patent itself lists several prior art references in its "Description of Related Art" section, which are relevant for this analysis.

Prior Art References and their Relevance to US11138997:

1. U.S. Pat. No.: 6,468,670 (issued October 22, 2002): Introduced a continuous ferromagnetic overlayer to increase Signal to Noise Ratio (SNR).
2. U.S. Pat. No.: 6,280,813 (issued August 28, 2001) and U.S. Pat. No.: 6,383,668 (issued May 7, 2002): Addressed thermal instability by replacing a single magnetic recording layer with two antiferromagnetically coupled ferromagnetic films (6,280,813) or a ferromagnetic layer coupled to a synthetic antiferromagnet (6,383,668) to reduce the demagnetizing field in longitudinal recording.
3. U.S. Pat. No. 5,583,727 (issued December 10, 1996): Proposed overcoming the thermal instability problem using thermally assisted recording.
4. Thiele et al., "FeRh/FePt exchange spring films for thermally assisted magnetic recording media," Applied Physics Letters, Vol. 82, Issue 17, April 2003, pp. 2859-2861: Suggested lowering the coercive field using an FePt/FeRh bilayer system with a hard layer exchange coupled to an antiferromagnetic layer that becomes ferromagnetic with low anisotropy upon heating.
5. R. H. Victora and X. Shen, "Composite Media for Perpendicular Magnetic Recording," IEEE Transactions on Magnetics, Vol. 41, No. 2, February 2005, pp. 537-542: Proposed magnetic multilayer structures with magnetically hard and soft layers, where magnetization remained uniform. They concluded that a decoupling layer was needed to decrease exchange coupling to reduce the coercive field.
6. Wang et al., "Composite media (dynamic tilted) media for magnetic recording," Applied Physics Letters, Vol. 86, April 2005, pp. 142504: Experimental work on two-layer composite media, concluding a coupling layer was required to decrease exchange coupling between soft and hard layers, in line with Victora and Shen.
7. Suess et al., "Exchange spring media for perpendicular recording," Applied Physics Letters, Vol. 87, July 2005, pp. 12504-12507: (Incorporated by reference in US11138997). Presented domain wall assisted recording on bilayers, where states with inhomogeneous magnetization were formed.
8. Y. Inaba et al., "Preliminary Study on (CoPtCr/NiFe)—SiO2 Hard/Soft-Stacked Perpendicular Recording Media," IEEE Transactions on Magnetics, Vol. 41, No. 10, October 2005, pp. 3136: Considered thin soft magnets coupled to thin hard magnets to keep magnetization uniform and parallel during reversal.
9. Suess et al., "Exchange spring recording media for areal densities up to 10 Tbit/in 2," Journal of Magnetism and Magnetic Materials, Vol. 290-291, 2005, pp. 551-554: (Available online December 18, 2004, and incorporated by reference in US11138997). Proposed a tri-layer structure with a hard layer at the bottom, a soft layer in the middle, and a hard layer on top.
10. Loxley et al., "Theory of Domain Wall Nucleation in a Two Section Magnetic Wire," IEEE Transactions on Magnetics, Vol. 37, July 2001, pp. 1998-2100: Discussed significant reduction of coercive field in a bilayer structure of an idealized magnetic wire.
11. Hagedorn, "Analysis of Exchange-Coupled Magnetic Thin Films," Journal of Applied Physics, Vol. 41, 1970, pp. 2491-2502: Showed a factor of five decrease in coercive field when a finite anisotropy in the soft layer was assumed.

Level of Ordinary Skill in the Art:

A person of ordinary skill in the art (POSITA) in this field would likely have a graduate degree (e.g., Masters or Ph.D.) in materials science, electrical engineering, or physics, with a specialization in magnetism, magnetic recording, or solid-state physics. They would be familiar with magnetic recording media architectures, concepts like anisotropy, coercivity, thermal stability, superparamagnetic limit, exchange coupling, and domain wall dynamics. They would also be capable of understanding and applying micromagnetic simulations and experimental results in the field of magnetic data storage.

Obviousness Analysis of Claims 1 and 7:

Both independent claims 1 and 7 define a magnetic recording system/medium with an exchange-coupled magnetic multilayer structure, comprising a hard magnetic storage layer and a softer nucleation host, where the nucleation host is formed on the hard magnetic storage layer, and comprises ferromagnetic layers with increasing anisotropy from layer to layer.

The core innovative aspects claimed in US11138997 revolve around:

• The specific layering order (nucleation host on the hard magnetic storage layer, where the hard layer is between the nucleation host and substrate).
• The nucleation host comprising multiple ferromagnetic layers with increasing anisotropy from layer to layer.
• The ability to separately adjust coercive field and thermal energy barrier due to this architecture.

Potential Obviousness Combinations:

Several prior art references individually or in combination disclose elements of US11138997. The challenge for obviousness is to establish a motivation for a POSITA to combine these elements in the manner claimed, with a reasonable expectation of success.

Combination 1: Victora & Shen (2005) + Suess et al. (2005 - "Exchange spring media for perpendicular recording") + Suess et al. (2005 - "Exchange spring recording media for areal densities up to 10 Tbit/in 2")

• Victora & Shen (2005) introduced the concept of magnetic multilayer structures with magnetically hard and soft layers for perpendicular magnetic recording to overcome the superparamagnetic limit. However, their model assumed uniform magnetization and suggested reducing exchange coupling with a decoupling layer.
• Suess et al. (2005 - "Exchange spring media for perpendicular recording") (incorporated by reference) directly addressed Victora & Shen's limitations by demonstrating that states with inhomogeneous magnetization (i.e., domain walls) were formed during reversal in exchange spring bilayers. This explicitly moves away from the uniform magnetization assumption of Victora & Shen and focuses on domain wall dynamics for switching.
• Suess et al. (2005 - "Exchange spring recording media for areal densities up to 10 Tbit/in 2") (incorporated by reference) further proposed a tri-layer structure (hard at bottom, soft in middle, hard on top). While the layering order is different from the claimed invention, this reference clearly teaches the use of multiple magnetic layers with varying hardness to create an exchange spring effect.

Motivation for Combination and Obviousness:

A POSITA, facing the writeability problem in perpendicular recording media, would be motivated to combine the general concept of hard/soft multilayer structures from Victora & Shen with the domain wall-assisted switching mechanism taught by Suess et al. (2005 - "Exchange spring media"). Recognizing the benefits of domain wall propagation, the POSITA would then look for ways to optimize this effect. Suess et al.'s earlier work on a tri-layer structure provided a clear teaching of using multiple layers with varying magnetic properties within an exchange spring context, even if the specific arrangement (hard/soft/hard) differs from the claims of US11138997.

The inventive step in US11138997 involves placing the nucleation host on the hard magnetic storage layer, with increasing anisotropy layers within the nucleation host. A POSITA seeking to improve domain wall nucleation and propagation for easier writing, while maintaining thermal stability, would consider varying the anisotropy profile. Hagedorn (1970) already described how the pinning field to push a domain wall from a softer to a harder layer depends on the difference in anisotropy constants. The idea of gradually increasing anisotropy to facilitate domain wall propagation would be a logical extension, as explicitly noted in US11138997, where it states, "If the number of layers is increased, this difference can be decreased leading to a reduction of the pinning and coercive field."

Therefore, a POSITA, motivated by the ongoing need to reduce the coercive field for writeability (as described in the "BACKGROUND" of US11138997), and having the understanding that domain wall nucleation and propagation are key mechanisms (Suess et al. 2005), could have explored different anisotropy profiles within multilayer structures. The concept of gradually increasing anisotropy to "smooth" the path for a domain wall, thereby reducing the coercive field while maintaining thermal stability (which is determined by the hardest layer, as per US11138997's disclosure), would have been an obvious design choice for optimization. The specific layering order (nucleation host on top of the hard layer) and the increasing anisotropy within the nucleation host, as claimed, would represent a predictable variation or optimization of known techniques to achieve a desired effect (reduced coercive field, maintained thermal stability) in exchange spring media.

Combination 2: Loxley et al. (2001) + Hagedorn (1970) + Any of the Suess et al. (2005) references.

• Loxley et al. (2001) showed that the coercive field in a bilayer structure could be significantly reduced due to domain wall nucleation. While it considered an idealized magnetic wire, the principle of domain wall-assisted reversal was established.
• Hagedorn (1970) quantified the dependence of the pinning field on the difference in anisotropy constants between layers. It also showed that a finite anisotropy in the soft layer could lead to a decrease in coercive field.
• Suess et al. (2005) references provide the context of practical exchange spring media for perpendicular recording.

Motivation for Combination and Obviousness:

A POSITA would understand from Loxley et al. and Hagedorn that tailoring the magnetic properties of adjacent layers to control domain wall propagation is crucial for reducing coercivity. Given the general objective of reducing the writing field, and the specific teaching from Hagedorn regarding the influence of anisotropy differences on pinning, a POSITA would be motivated to systematically vary anisotropy across multiple layers to further reduce the pinning force and, consequently, the coercive field. The concept of "increasing anisotropy from layer to layer" within the nucleation host, and placing this on the hard layer, is a logical step in extending the principles laid out in these earlier works to optimize the exchange spring effect for practical recording media. The patent itself notes that "If the number of layers is increased, this difference can be decreased leading to a reduction of the pinning and coercive field." This statement suggests that increasing the number of layers with incrementally increasing anisotropy to "smooth" the magnetic gradient was already a known or derivable principle for reducing coercivity.

Claim 7 Specifics: "at least two of the ferromagnetic layers are coupled with a thin exchange coupling layer."

Claim 7 adds the specificity of using a thin exchange coupling layer between at least two ferromagnetic layers within the nucleation host. The patent itself states that "The exchange coupling can be direct or via a thin coupling layer in order to achieve strong coupling." It also notes that optional coupling layer 22 (between the nucleation host and hard magnetic storage layer) may have a thickness between 0.1 nm and 3 nm, and can provide strong exchange coupling. Given that coupling layers were a known element in magnetic recording media for achieving desired exchange coupling (e.g., Wang et al. (2005) discusses their role in decreasing exchange coupling), and the patent explicitly states they can be used to achieve strong coupling within the broader exchange spring context, a POSITA would find it obvious to apply such known coupling layers within a multilayer nucleation host to ensure strong exchange coupling between its constituent ferromagnetic layers. This would be a matter of routine design choice or optimization for achieving the desired magnetic interaction.