Obviousness

Obviousness Analysis under 35 U.S.C. § 103

A patent claim is obvious if "the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains." (35 U.S.C. § 103). The motivation to combine prior art references can come from the knowledge of those skilled in the art, from the prior art reference itself, or from the nature of the problem to be solved. It's important to note that merely identifying all elements of an invention in the prior art is not enough; there must be a clear reason or rationale for a person of ordinary skill in the art (PHOSITA) to combine those elements in the claimed manner. The combination need not be "the best option, only a suitable option."

The independent claim, Claim 1, describes a magnetic recording system. It includes a writing head and a disk with a magnetic recording medium, which comprises an essentially non-magnetic substrate, an underlayer, and an exchange-coupled magnetic multilayer structure. This structure further includes a hard magnetic storage layer and a nucleation host. The hard magnetic storage layer is a perpendicular anisotropy material with a coercive field Hc > 0.5 T. The nucleation host has a coercive field Hn < Hs and is formed on the hard magnetic storage layer. The nucleation host itself contains at least a first ferromagnetic layer with anisotropy K1 and a second ferromagnetic layer between the first layer and the hard magnetic storage layer with an increased anisotropy K2 (K2 > K1), with an exchange coupling layer between the first and second ferromagnetic layers.

Combination 1: Suess et al. (US20070292720A1 or equivalent) in view of Victora and Shen (2005)

Prior Art References:

• Suess et al. (US20070292720A1): This patent application (which is an earlier publication of the same family as US12020734B2) describes a multilayer exchange spring recording media consisting of a magnetically hard magnetic storage layer strongly exchange coupled to a softer nucleation host. The nucleation host can consist of one or more ferromagnetic coupled layers, and for a multilayer nucleation host, the anisotropy increases from layer to layer. The patent also mentions that the nucleation host decreases the coercive field significantly while keeping the energy barrier of the hard layer almost unchanged, addressing the writeability problem. Suess et al. explicitly discusses "exchange spring media" where the recording media consists of exchange-coupled soft and hard magnetic layers, allowing good writeability due to the soft layer while maintaining thermal stability of the hard layer.
• Victora and Shen (2005): In their paper "Composite Media for Perpendicular Magnetic Recording," Victora and Shen proposed magnetic multilayer structures composed of magnetically hard and magnetically soft layers. Their model, however, assumed the magnetization of the soft and hard parts of each grain remained uniform, and to decrease the coercive field, the exchange coupling between these layers had to be reduced with a decoupling layer.

Motivation to Combine:

A person having ordinary skill in the art (PHOSITA) in the field of magnetic recording media would have been motivated to combine the teachings of Suess et al. and Victora and Shen to improve the writeability and thermal stability of high-density magnetic recording media.

Suess et al. explicitly addresses the writeability problem in perpendicular recording media by using a multilayer exchange spring recording media where a hard magnetic storage layer is strongly exchange coupled to a softer nucleation host. The core idea is that the anisotropy increases from layer to layer within the nucleation host.

While Victora and Shen also proposed magnetic multilayer structures with hard and soft layers to address recording density challenges, their approach focused on reducing exchange coupling for coercive field decrease and assumed uniform magnetization within layers. Suess et al., however, differentiates itself by stating that "this was in contrast to the paper 'Exchange spring media for perpendicular recording,' . . . where states with inhomogeneous magnetization were formed." This suggests Suess et al. was aware of Victora and Shen's work and proposed an alternative that did not rely on reducing the exchange coupling to decrease coercive field.

However, Claim 1 of US12020734 specifies that the first and second ferromagnetic layers within the nucleation host are exchange coupled with an exchange coupling layer. While Suess et al. (the prior art publication) mentions that the overall exchange coupling between the nucleation host and the hard magnetic storage layer can be "direct or via a thin coupling layer," it doesn't explicitly detail an internal exchange coupling layer between the ferromagnetic layers within the nucleation host.

Therefore, a PHOSITA, recognizing the benefits of the graded anisotropy in the nucleation host taught by Suess et al. for addressing the writeability problem, and being familiar with the general concept of using coupling layers in multilayer magnetic structures (as discussed by Victora and Shen for decoupling, or by Suess et al. itself for coupling the nucleation host to the hard layer), would have found it obvious to introduce an exchange coupling layer between the internal layers of the nucleation host to ensure strong exchange coupling and thus facilitate the domain wall propagation critical to the "exchange spring" mechanism. The goal would be to optimize the benefits of the gradually increasing anisotropy in the nucleation host, as shown by Suess et al. to reduce the coercive field and maintain thermal stability. This would be a predictable alteration to achieve a known result in the field of multilayer magnetic recording media.