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MMM 2022

November 07, 2022

Minneapolis, United States

Evaluation of magnetic flux density distribution of magnetic domains recorded in racetrack memory by TMR head

Racetrack memory is expected to be a memory device that supports the information society because of its high speed and low power consumption. Although many studies have been conducted to improve the speed of magnetic domain wall movement, few studies have been conducted from the viewpoint of Joule heat. Therefore, we have investigated the relationship between Joule heat and domain wall motion in the 2022 Joint MMM-INTERMAG.(1) In elucidating the mechanism of this current-driven domain wall motion, although the domain wall width is an essential parameter for improving the domain wall moving speed and the critical current density, the details of the domain wall width are still unknown. Generally, MFM is used for magnetic domain observation. In MFM, as shown in FIG. 1, it is possible to observe the magnetic domain shape by vibrating a thin magnetic needle up and down, but it is challenging to investigate the accurate magnetic flux density distribution. However, suppose the TMR head can be contacted with the sample and scanned. In that case, the distance between the sample and the TMR head can be kept constant to measure the accurate magnetic flux density distribution created by the magnetic recording domain. FIG. 2 shows a TMR head scan image of a magnetic domain recorded in a racetrack memory having a width of 10 μm and a length of 100 μm. The result of line scanning by enlarging this domain wall is also shown in the figure. The recording material is TbCo ferrimagnetic material, the domain wall movement is fast, and the critical current density is small (2). Despite the small saturation magnetization due to ferrimagnetism and thin film (10 nm), the TMR head could measure a clear change in magnetic flux density within a range of ± 20 mT.

(1) Sota, K. et al. Relationship between pulse width and domain wall velocity in current induced domain wall motion in GdFeCo wire and the effect of joule heat on the racetrack memory, Joint MMM-Intermag Conference, 3628926 (2022)
(2) Sina, R. et al. Fast Current Induced Domain Wall Motion in Compensated GdFeCo Nanowire, Joint MMM-Intermag Conference, 3786257 (2022)

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