22toward zero emission, is important. L10-FePt nano-granular film All-optical measurement setups the THz magnetization dynamics were developed and constructed in NIMS. By using these newly developed measurement systems, fast magnetization dynamics in Cu2Sb-type MnCrAlGe ultrathin films was investigated. A ferromagnetic metal nanolayer with a large perpendicular magnetic anisotropy (PMA), small saturation magnetization Ms, and small magnetic damping constant α is a crucial requirement for high-speed spintronic devices. We have discovered that this ultrathin film showed relatively small damping constant of α=0.012 while it keeps large PMA above 4.0 T with a film thickness of 5.0 nm.(Fig.1) It was demonstrated that Cu2Sb-type MnCrAlGe is promising material for future spintronic devices in order to realize Society5.0. [1]We have also investigated the thermal modulation of fast magnetization dynamics for a L10-FePt continuous thin film in Research Digest to investigate order to design switching parameters in HAMR media. By analyzing magnetic field dependence of precession frequency and amplitude decay time, intrinsic damping constant was evaluated using Kittel’s formula with PMA distribution. It was clarified that the temperature dependence of the intrinsic damping constant exhibit minimum at 530K.(Fig.2) This complexed temperature dependence not predicted in theoretical studies[2] might be caused from thermal expansion or modulation of density of states, which are difficult to be taken into account the theoretical calculation.[3] Fig. 1. (a) Schematic illustration of TRMOKE measurement for MnCrAlGe thin film. (b)Time and (c)frequency domain TRMOKE spectra with various magnetic fields. Fig. 2. (a)Temperature dependence of the intrinsic damping constant for the L10-FePt continuous film. Solid triangles and squares show the theoretical data predicted in previous studies.[2] References 1) Y. Sasaki, et al., Small 18, 2200378 (2022). 2) M. Strungaru, et al., Phys. Rev. Appl. 14, 014077 (2020)., R. Hiramatsu, et al., Appl. Phys. Exp. 15, 013003 (2022). 3) Y. Sasaki, et al., ACS Appl. Nano Mater. 6, 5901-5908 (2023).1. Outline of ResearchSociety 5.0 is a future social model, which is highly integrated cyberspace and physical space, proposed by the Cabinet Office, Government of Japan. In this social model, we can obtain technical knowledges and solutions unconsciously by using AI computing and big data analysis. In order to realize this society model, a data center will be connected to a lot of sensing devices for collecting the big data such as climate, temperature, human health, location information, transport information, etc. Since data traffic and amount of data processing in the data center will drastically increase in coming Society 5.0, huge energy will be consumed in the current network system. In order to realize the sustainable society low energy consumption and ultrafast processing system is required. In order to reduce the energy consumption in the data center, continuous growth of the recording density in the data storage technology is promising material in hard disk drive (HDD) for future high-density storage in terms of large magnetic anisotropy energy and high coercivity. However, since switching costs huge magnetic field due to its high coercivity, another method to control the magnetization switching is proposed, such as a thermal heating or microwave assisted magnetic recording (HAMR or MAMR). In order to realize the effective switching with low energy, the investigation on the magnetization dynamics with the assistance of external energy is necessary. Furthermore, fast operation of data processing using non-volatile memory device is also required for Society 5.0. Therefore, spintronic memory device has been attracted as a future non-volatile memory device. For low energy and fast processing are emergent issues for future IoT society. In this research, THz magnetization dynamics in L10-FePt and other spintronic materials will be investigated by combining newly developed all-optical measurement system.2. Research ActivitiesAll-optical Control of THz Magnetization Dynamics in L10-FePt Nano-granular FilmYuta SASAKI
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