Prior art

To identify the most relevant prior art for US patent 11138997, I need to consult the patent's own citations. The provided patent text includes a "Citations" section. I will analyze these citations to determine their relevance and potential anticipation of the claims.

Here are the most relevant prior art references cited within US11138997, along with their details and an assessment of which claim(s) they potentially anticipate under 35 U.S.C. § 102:

1. US6468670B1

• Full Citation: US6468670B1 - Magnetic recording disk with composite perpendicular recording layer
• Publication Date: October 22, 2002 (Filing Date: January 19, 2000)
• Brief Description: This patent introduces a continuous ferromagnetic overlayer to increase the Signal to Noise Ratio (SNR) in magnetic recording.
• Potential Anticipation: This patent addresses increasing SNR with a continuous ferromagnetic overlayer, which is a general improvement in magnetic recording media. While US11138997 focuses on a multilayer exchange spring structure with a soft nucleation host to reduce coercive field and maintain thermal stability, US6468670B1's concept of an "overlayer" might broadly anticipate the idea of an additional magnetic layer on a recording medium. However, the specific structure and function (exchange spring, varying anisotropy, soft nucleation host) claimed in US11138997 (especially in claims 1 and 7) appear distinct. Thus, it's unlikely to fully anticipate claims 1 or 7, but might be considered for broad concepts of multi-layered magnetic recording.

2. US6280813B1

• Full Citation: US6280813B1 - Magnetic recording media with antiferromagnetically coupled ferromagnetic films as the recording layer
• Publication Date: August 28, 2001 (Filing Date: October 8, 1999)
• Brief Description: This patent addresses thermal instability by replacing a single magnetic recording layer with two ferromagnetic films that are antiferromagnetically coupled across a nonferromagnetic spacer film. This reduces the demagnetizing field of the bits for longitudinal magnetic recording.
• Potential Anticipation: This patent describes antiferromagnetically coupled films for thermal stability. While US11138997 mentions that the coupling between the nucleation host and the hard magnetic storage layer may be antiferromagnetic, its core innovation lies in the "exchange spring" effect achieved through a softer nucleation host with increasing anisotropy from layer to layer (as per claims 1 and 7) and a focus on perpendicular recording. The general concept of multiple coupled ferromagnetic layers for thermal stability has some overlap, but the specific characteristics of the nucleation host and the exchange spring mechanism as defined in claims 1 and 7 are not explicitly present.

3. US6383668B1

• Full Citation: US6383668B1 - Magnetic recording media with antiferromagnetically coupled host layer for the magnetic recording layer
• Publication Date: May 7, 2002 (Filing Date: March 27, 2000)
• Brief Description: This patent addresses thermal instability by using a ferromagnetic layer coupled to a synthetic antiferromagnet. This also reduces the demagnetizing field of the bits in longitudinal magnetic recording.
• Potential Anticipation: Similar to US6280813B1, this patent focuses on antiferromagnetic coupling for thermal stability and demagnetizing field reduction, primarily for longitudinal recording. Again, the specific "exchange spring" multilayer structure with varying anisotropy in the nucleation host, as defined in claims 1 and 7 of US11138997 for perpendicular recording, is not directly anticipated.

4. US5583727A

• Full Citation: US5583727A - Multiple data layer magnetic recording data storage system with digital magnetoresistive read sensor
• Publication Date: December 10, 1996 (Filing Date: May 15, 1995)
• Brief Description: This patent proposes overcoming thermal instability by employing thermally assisted recording.
• Potential Anticipation: This reference describes thermally assisted recording, a different approach to the writeability problem than the exchange spring mechanism of US11138997. It is unlikely to anticipate claims 1 or 7 directly, as the structural elements and magnetic behavior described are fundamentally different.

5. US20030108721A1

• Full Citation: US20030108721A1 - Thermally - assisted magnetic recording disk with recording layer exchange- coupled to antiferromagnetic-to-ferromagnetic switching layer
• Publication Date: June 12, 2003 (Filing Date: December 11, 2001)
• Brief Description: This patent describes a bilayer system (FeRh/FePt) to lower the coercive field using thermally assisted recording. After heating, the antiferromagnetic layer (FeRh) becomes ferromagnetic with a large magnetic moment and low magnetocrystalline anisotropy, acting as a soft layer to reverse the hard layer (FePt).
• Potential Anticipation: This is a more relevant reference as it discusses lowering the coercive field using an exchange-coupled bilayer system and the concept of a "soft layer" assisting the reversal of a "hard layer." However, the mechanism is thermally assisted recording, where the soft layer's properties change with temperature. US11138997 (claims 1 and 7) focuses on a multilayer nucleation host with increasing anisotropy from layer to layer at operating temperature, to achieve an exchange spring effect without necessarily relying on thermal assistance to change the magnetic properties of the layers during writing. While the idea of a soft layer assisting a hard layer is similar, the specific structure (multilayer nucleation host with increasing anisotropy) and the non-thermal-assisted operation distinguish claims 1 and 7.

6. US20070243418A1

• Full Citation: US20070243418A1 - Perpendicular magnetic recording medium with laminated recording layers formed of exchange-coupled ferromagnetic layers
• Publication Date: October 18, 2007 (Filing Date: April 12, 2006)
• Brief Description: This patent describes a perpendicular magnetic recording medium with laminated recording layers formed of exchange-coupled ferromagnetic layers. The abstract of US11138997 itself refers to "multilayer exchange spring recording media" and the context of overcoming the "writeability problem" in perpendicular recording media.
• Potential Anticipation: This reference is highly relevant as it explicitly discusses "perpendicular magnetic recording medium with laminated recording layers formed of exchange-coupled ferromagnetic layers." This directly overlaps with the general description of US11138997. The priority date of US11138997 is June 17, 2006, while the filing date of US20070243418A1 is April 12, 2006, making it prior art. Without a detailed analysis of the specific claims of US20070243418A1, it's difficult to definitively state anticipation. However, the title and description strongly suggest it could anticipate broader aspects of both claims 1 and 7, particularly the concept of exchange-coupled multilayer structures for perpendicular recording. The key differentiator for US11138997's claims 1 and 7 would be the specific arrangement of the hard magnetic storage layer and the nucleation host, and the increasing anisotropy constant K from layer to layer within the nucleation host.

7. US7550210B2

• Full Citation: US7550210B2 - Perpendicular magnetic recording medium with multiple exchange-coupled magnetic layers having substantially similar anisotropy fields
• Publication Date: June 23, 2009 (Filing Date: March 9, 2006)
• Brief Description: This patent describes a perpendicular magnetic recording medium with multiple exchange-coupled magnetic layers having substantially similar anisotropy fields.
• Potential Anticipation: This patent is also highly relevant due to its focus on "perpendicular magnetic recording medium with multiple exchange-coupled magnetic layers." The priority date of US11138997 is June 17, 2006, and the filing date of US7550210B2 is March 9, 2006, making it prior art. The key distinction from US11138997 (claims 1 and 7) would be the phrase "substantially similar anisotropy fields," whereas US11138997 explicitly claims "ferromagnetic layers with increasing anisotropy constant K from layer to layer" in the nucleation host. This difference in anisotropy gradient is a crucial element that might prevent direct anticipation of claims 1 and 7, but it certainly addresses the same problem space with similar components.

8. US7687157B2

• Full Citation: US7687157B2 - Perpendicular recording media having an exchange-spring structure
• Publication Date: March 30, 2010 (Filing Date: February 4, 2005)
• Brief Description: This patent describes perpendicular recording media having an exchange-spring structure.
• Potential Anticipation: This patent is exceptionally relevant as it explicitly mentions "perpendicular recording media having an exchange-spring structure." The filing date of February 4, 2005, makes it clear prior art to US11138997's priority date of June 17, 2006. This reference directly covers the core inventive concept of US11138997's title and abstract. A detailed comparison of the claims of US7687157B2 with claims 1 and 7 of US11138997 would be necessary. Claims 1 and 7 of US11138997 specifically detail the nucleation host being formed on the hard magnetic storage layer, and the nucleation host comprising ferromagnetic layers with increasing anisotropy constant K from layer to layer. If US7687157B2 describes these specific structural and anisotropy gradient features, it could potentially anticipate claims 1 and 7. The description of the current patent states, "The paper “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 18 Dec. 2004) by Suess et al., incorporated herein by reference in its entirety, proposed a tri-layer structure which was composed of a hard layer at bottom, a soft layer in the middle and a hard layer on top." and "The paper “Exchange spring media for perpendicular recording,” Applied Physics Letters, vol. 87, 30. June 2005, pp. 012504, by Suess et al., incorporated herein by reference in its entirety, domain wall assisted recording on bilayers was presented." These publications by the same inventor suggest that the underlying concepts of exchange spring media by Suess existed prior to the filing of US11138997. US7687157B2, with its earlier filing date and title, likely embodies some of these earlier concepts.

Key takeaway for anticipation: The later-filed US11138997 likely seeks to differentiate itself from these earlier "exchange spring" and "multilayer perpendicular recording" patents by emphasizing the specific architecture of the nucleation host (e.g., its position relative to the hard layer, its internal multilayer structure, and the increasing anisotropy gradient within it), and the precise control over the coercive field and thermal stability (as defined by metrics like the change in slope 'k' and squareness 'S'). A thorough anticipation analysis would require comparing the specific claim language of US11138997 against the full disclosures of these prior art patents, especially US20070243418A1, US7550210B2, and US7687157B2.