Spintronics advances Efficient Magnetization Direction Control for Magnetite for High-Density Spintronic Memory Devices.

Scientists have developed a strategy that is energy efficient to reverse the magnetization direction or spin orientation in magnetite at room temperatures.

In the past few decades, traditional electronics has reached its technical limits in computing, information technology, and communications. This has prompted the need for new devices that can manipulate electron currents. Spintronics is one of the most exciting areas of applied physics. It studies devices that use the spin of electrons to perform specific functions. However, measuring, altering, or working with this fundamental quantum property takes work.

Current spintronic devices, such as magnetic tunnel junctions, suffer from limitations like high power consumption, low operating temperatures, and strict material selection. A team of Japanese scientists from the Tokyo University of Science, and the National Institute for Materials Science, Japan, published a study in ACS. Nano. It demonstrates a simple but effective strategy to control the magnetization angle of magnetite (Fe 3O 4), a common ferromagnetic substance.

Figure 1. Figure 1. Credit: Tohru Higuchi, Tokyo University of Science

The team created an all-solid reduction/oxidation (“redox”) transistor that contained a thin film Fe 3O 4 on magnesium oxide and a lithium silicate electrolyte doped in zirconium (Figure 1). By inserting lithium ions into the solid electrolyte, it was possible to rotate the magnetization angle at room temperature and change the electron carrier densities.

Tohru Higuchi, an Associate Professor at the Tokyo University of Science, is one of the authors of the published paper. He says, “Using a voltage to insert lithium ions in a liquid electrolyte into a ferromagnet, we have developed a spinning device that can rotate magnetization with lower power consumption than magnetization rotation via spin current injection.” The magnetization rotation is caused due to the alteration of spin-orbit coupling by electron injection into a ferromagnet.

Figure 2. Figure 2. The rotation becomes more evident at voltages greater than 0.7 V but is irreversible because of permanent structural changes in the magnetite phase. Credit: Tohru Higuchi, Tokyo University of Science

Unlike previous attempts, the new method leverages a reversible electrochemical reaction, which relies on strong magnetic fields and injects spin-tailored currents. The external voltage causes lithium ions to migrate from the top of the lithium cobalt oxide electrode through the electrolyte and onto the magnetic Fe O 4 layer. These ions can then insert themselves into the magnetite structure and form Li xFe 3O 4. This causes a noticeable rotation in its magnetization angle due to changing charge carriers.

Scientists were able to change the magnetization angle by about 10 degrees. Although 56deg rotation was possible by increasing the external voltage, the scientists found that the magnetization angle couldn’t be reversed completely (Figure 2). Higuchi explains, “We found that the irreversible magnetization angle rotates caused by a change to the crystalline structure magnetite due to excess lithium ions.”

Scientists have made a significant breakthrough in controlling magnetization to develop spintronic devices. The device’s structure is simple. According to Dr. Takashi Takashi Tsuchiya (Principal Researcher at NIMS), the corresponding author of this study, “By controlling magnetization direction at room temperatures due to the insertion lithium ions into Fe O 4, it is possible to operate with much less power than the magnetization rotation using spin current injection.” The element is simple to operate.

While much is still to be done to exploit this device fully, spintronics’ imminent rise will open up many new and exciting applications. “In the future, we will attempt to achieve a rotational angle of 180deg in magnetization,” Dr. Kazuya Tarabe, principal investigator at the International Center for Materials Nanoarchitectonics (NIMS) and co-author of this study. “This would allow us to create high-density, large-capacity spintronic memory devices with high capacity and neuromorphic devices which mimic biological neural systems.” Other applications of spintronics include the highly coveted field of quantum computing.

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