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Magnetic recording media made 3-dimensional: NIMS demonstrates expectations for 10 terabits per square inch


A research group led by Distinguished Researcher P. Tozman and Group Leader Yukiko Takahashi at the Research Center for Magnetic and Spintronics Materials, National Institute for Materials Science (NIMS), along with U.S. manufacturer Seagate Technology LLC and Tohoku University, has announced that they have demonstrated multi-level recording is possible in hard disk drives (HDD) used as recording devices in data centers by making the magnetic recording media three-dimensional. Unlike conventional two-dimensional recording layers, the recording density is greatly increased by stacking the recording layers three-dimensionally. Ultra-high-density HDDs exceeding 10 terabits/square inch are expected to be realized. The results were published in the academic journal Acta Materialia on March 24.

In order to promote data center capacity for the storage of digital information, it is necessary to increase the density of storage devices − namely, HDDs. The current recording density of commercial HDDs is 1.5 terabits per square inch. However, according to the roadmap announced by the ASRC in the U.S., 4 terabits per square inch should be achieved by 2028 and 10 terabits per square inch by 2034.

Currently, the perpendicular magnetic recording method is used, in which the magnetization of the bits is oriented vertically. However, to achieve 4 terabits per square inch requires HAMR, in which the temperature of the magnetic recording medium is raised. HAMR is a heat-assisted magnetic recording method using iron platinum (FePt) with high magnetic anisotropy that can increase recording density from the current 1.5 terabits per square inch. NIMS and Seagate Technology jointly developed a prototype of FePt-based media for HAMR in 2008, and they commercialized it in 2020. Meanwhile, when the size of FePt particles becomes 4 nm or smaller, the magnetization begins to fluctuate due to heat, making it difficult to achieve 10 terabits per square inch, and a magnetic recording method based on a new principle has been deemed necessary.

In this study, the research group used FePt as the recording medium material and fabricated a three-dimensional FePt medium using Ru (ruthenium) as a spacer layer to make the upper and lower two FePt layers magnetically independent. In the three-dimensional magnetic recording method, in which recording layers are stacked three-dimensionally, bits are also arranged perpendicular to the film, and recording is performed by adjusting the laser output for writing with a difference of about 100K in the Curie point of each magnetic recording layer. Examination of the magnetization and heat-assisted magnetization curves revealed two magnetization reversals and Curie points (temperature at which the ferromagnetic material changes to paramagnetic) corresponding to the upper and lower FePt layers, respectively. This means that three-dimensional multi-level recording is possible by adjusting the output of the writing laser. Writing simulations based on the microstructure and magnetic properties of the fabricated FePt media demonstrated multi-level recording.

In the future, they aim to downsize FePt particles, improve the orientation and magnetic anisotropy of the upper FePt layer, and develop further multilayer FePt layers to realize a media structure suitable for practical use as a high-density HDD. Takahashi said, "In three-dimensional magnetic recording, unique microstructures must be stacked three-dimensionally, and magnetic properties must also be controlled. Although there are many material science issues that need to be addressed to achieve practical application, such as realization of fine particle size and columnar structure of FePt, we hope to reach our goal by feeding back the knowledge obtained from microstructure observation, which is one of our strengths, to the process."

Journal Information
Publication: Acta Materialia
Title: Dual-layer FePt-C granular media for multi-level heat-assisted magnetic recording
DOI: 10.1016/j.actamat.2024.119869

This article has been translated by JST with permission from The Science News Ltd. ( Unauthorized reproduction of the article and photographs is prohibited.

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