VP23-06 Stable Data Store Operation in Magnetic Nanowire Memory with Stepped Structures Observed by Magneto-optical Kerr Effect Microscopy
Creators: Daisuke Kato
Kei Ogura
Nobuhiro Kinoshita
Yasuyoshi Miyamoto;
Publisher: name: IEEE
Year: 2025

We have been studying the magnetic nanowire (NW) memory, which uses current-driven domain wall motion to shift the written magnetic domains, to achieve ultra-high data transfer rate for future "immersive media" storages. In our previous work[1], we tried to install periodic ratchet trap sites along NW for the constant domain shift. However, since these ratchets induced the Bloch domain wall mode and their trapping energy was too high, the uniform shift of domains was obstructed. While the NW with stepped structures exhibited the chiral domain wall mode and offered the prospect of achieving a constant domain shift length[2]. In this study, we report the successful memory operation in the stepped NW observed by magneto-optical Kerr effect microscopy (MOKE). Fig.1 shows a microscopic image of the fabricated NW memory device. To define the unit shift length, periodic SiN(4) steps with a width of 3 μm and a pitch of 6 μm were formed under the NW consisting of Pt(3)/[Co(0.35)/Tb(0.85)]4 (units in nm). The width of the NW was 3 μm. A writer for forming domains was placed orthogonally to the NW with the insertion of an insulating layer. The experimental procedure is as follows: 0. initialize (the magnetic direction in NW is set downward by an external field of 1kOe), 1. write (a bidirectional field is generated by a current applied to a writer, which forms domains in NW), 2. drive (the written domains are shifted along NW by a drive current) By repeating write and drive, sequential binary data is stored in NW. The current density for write and drive was set to 4.1 and 9.0 MA/cm2, respectively. We tried to store 7-bits consisting of "1101110" data queue in the NW as illustrated in Fig.2(a). Fig.2(b) shows the MOKE image of the data-stored NW, where the dark and bright regions correspond to "0" and "1", respectively, and that 7-bits of data could be regularly stored by defining the domain length and shift length at intervals of the stepped structures under the NW. These results suggest that binary information can be stored in this memory structure in a first-in-first-out manner.References: [1]M. Takahashi et al.: MMM2022, IPA-05 (2022) [2]D. Kato et al.: MMM2023, DG-06 (2023)
We have been studying the magnetic nanowire (NW) memory, which uses current-driven domain wall motion to shift the written magnetic domains, to achieve ultra-high data transfer rate for future "immersive media" storages. In our previous work[1], we tried to install periodic ratchet trap sites along NW for the constant domain shift. However, since these ratchets induced the Bloch domain wall mode and their trapping energy was too high, the uniform shift of domains was obstructed. While the NW with stepped structures exhibited the chiral domain wall mode and offered the prospect of achieving a constant domain shift length[2]. In this study, we report the successful memory operation in the stepped NW observed by magneto-optical Kerr effect microscopy (MOKE). Fig.1 shows a microscopic image of the fabricated NW memory device. To define the unit shift length, periodic SiN(4) steps with a width of 3 μm and a pitch of 6 μm were formed under the NW consisting of Pt(3)/[Co(0.35)/Tb(0.85)]4 (units in nm). The width of the NW was 3 μm. A writer for forming domains was placed orthogonally to the NW with the insertion of an insulating layer. The experimental procedure is as follows: 0. initialize (the magnetic direction in NW is set downward by an external field of 1kOe), 1. write (a bidirectional field is generated by a current applied to a writer, which forms domains in NW), 2. drive (the written domains are shifted along NW by a drive current) By repeating write and drive, sequential binary data is stored in NW. The current density for write and drive was set to 4.1 and 9.0 MA/cm2, respectively. We tried to store 7-bits consisting of "1101110" data queue in the NW as illustrated in Fig.2(a). Fig.2(b) shows the MOKE image of the data-stored NW, where the dark and bright regions correspond to "0" and "1", respectively, and that 7-bits of data could be regularly stored by defining the domain length and shift length at intervals of the stepped structures under the NW. These results suggest that binary information can be stored in this memory structure in a first-in-first-out manner.References: [1]M. Takahashi et al.: MMM2022, IPA-05 (2022) [2]D. Kato et al.: MMM2023, DG-06 (2023)