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日本語

In recent years the volume of information being distributed across the world has sharply risen due to new technologies such as high-speed with mass date transfer of the Internet and 8K broadcasting. In response to this trend, there is increasing demand for an innovative method for storing large volumes of data at ultra-high recording density and at ultra-high speed. Magnetic-holographic memory is one type of technology apparently capable of meeting this demand, since it can be used to record 1 TB worth of data (equivalent to the total capacity of 40 Blu-ray discs, each with a typical capacity of 25 GB) on a disc the size of a DVD or Blu-ray disc.

In magnetic hologram recording, a medium is magnetized in one direction; then the medium is irradiated with an information-bearing beam (signal beam) and a reference beam; and the resulting interference pattern is recorded in the form of the difference in magnetization directions. When this recording proceeds with an external magnetic field applied to it, the recording of the difference in magnetization directions becomes clearer. The latter process is called magnetically assisted recording.

The research group led by Yuichi Nakamura has applied this magnetically assisted recording technology to magnetic-holographic memory and, for the first time in the world, succeeded in reducing recording energy consumption and achieving error-free data reconstruction.

Through simulation, the group investigated the size of the stray magnetic field required for magnetization reversal in magnetic hologram recording. As a result, they found that the thinner the medium, the smaller the necessary stray magnetic field and the less clear the hologram recording. They also proved through experiments that magnetically assisted recording yields a clear magnetic hologram even with a thin medium, and the magnetic hologram yields a bright reconstruction beam upon irradiation with a reference beam. Through further experiments, they found that magnetically assisted recording and reconstruction of two-dimensional data yields clear reconstruction images. As a result of this research, the group have achieved a world first by managing a significant reduction in errors in data recording and reconstruction for low energy consumption as well as error-free recording and reconstruction with magnetic-holographic memory.

"Until now it has been difficult to obtain a clear reconstruction image with a magnetic hologram, due to strict requirements for material characteristics, optical conditions, and so on. Using magnetically assisted recording, we have relaxed these requirements and also improved the reconstruction performance of recording media. This technology is promising for the future application of magnetic-holographic memory," says first author Shirakashi.

The research group intends to proceed with their work to improve recording density, and their goal is to apply this technology to make a portable, ultra-high-density and high-speed optical information storage medium (outperforming Blu-ray discs) capable of storing high-volume contents from various sources including 8K Super Hi-Vision broadcasting and 3D films; and to enable wide application of this technology in various types of storage systems, including archive and cold storage for storing information such as medical image data, SNS data on the Internet, and high-volume data in data centers.

This work was supported in part by Grants-in-Aid for Scientific Research (S) 26220902 and (A) 15H02240.