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家田 淳一; 岡安 悟; 武山 昭憲*; 針井 一哉*; 大島 武*; 石田 真彦*; 齊藤 英治
no journal, ,
We investigate irradiation tolerance against gamma-rays of a prototypical spin-driven thermoelectric (STE) device based on Y
Fe
O
/Pt heterostructures. The past study has proved that the STE device was rad-hard against the gamma-irradiation dose up to 0.3 MGy. In this study, we assess the radiation hardness in severer environments, such as higher dose levels, higher ambient temperatures, and water steam, assuming the future RTG usage near the spent nuclear fuel storage. We show that the YFeO/Pt STE device has tolerance to irradiation of gamma rays up to 0.9 MGy even at 150 
C. On the other hand, we observe the performance degradation of the STE device by the gamma-irradiation under the water steam. From a control experiment without gamma-rays, the irradiation is irrelevant, and the damage is caused solely by the water steam effect. To avoid the damage, it is found that the thicker Pt film (10 nm) in the STE device is effective. Therefore, it was clarified that the STE device has fundamentally high resistance to gamma rays.
山本 慧; 紅林 秀和*
no journal, ,
Motivated by the importance of non-linearity in general in quantum manipulation of cavity photons, we study the non-linear spin wave instability when a magnetic film is strongly coupled to a microwave resonator mode. We show both experimentally and theoretically that when the input driving power exceeds a certain threshold, the first-order Suhl instability for the spin waves manifests itself as an apparent closure of the anti-crossing gap in the microwave reflection spectrum of the coupled system. We identify its mechanism to be the blocking of hybridisation between the Kittel mode magnon and the resonator photon by a coherent back reaction from the unstable magnon pair.
荒木 康史; 家田 淳一
no journal, ,
We present a theory of current-induced torques on magnetic textures in the presence of strong spin-orbit coupling (SOC). Based on spin-momentum locking (SML) due to strong SOC, we phenomenologically classify the electrically induced torques on the magnetization into the four parts: whether the torque acts on uniform magnetization or nonuniform textures, and whether the torque depends on the transport time or not. From this classification, we point out that the "intrinsic" torques insensitive to the transport time arise from the anomalous velocity and SML. We especially point out an intrinsic torque acting on magnetic textures, which we call the "topological Hall torque (THT)". While the conventional spin-transfer torque (STT) is driven by the transport current and suffers from energy dissipation by the Joule heating, the THT arises from the anomalous velocity from the momentum-space topology and is thus capable of manipulating magnetic textures non-dissipatively, even in centrosymmetric crystals. To illustrate the significance of the THT, we show our model calculation in a metallic ferromagnet. The Weyl points due to the band inversion by SOC gives rise to a large THT acting on a magnetic domain wall therein. Its magnitude becomes compatible to the nonadiabatic STT with the unusual size of the nonadiabaticity parameter 
. We also demonstrate the experimental measurement of the THT from the current-induced domain wall motion in the metallic ferromagnet SrRuO
. The idea of the THT may help design the spintronics device highly efficient without building any complex heterostructures.
鈴木 和也; 一ノ瀬 智弘*; 飯浜 聡*; 門馬 簾*; 鎌田 尚樹*; 水上 成美*
no journal, ,
垂直磁気トンネル接合(p-MTJ)は、磁気抵抗ランダムアクセスメモリ,磁気センサー,高周波デバイスなどの豊富なアプリケーションのためのキーデバイスである。用途に応じた適切な磁気特性が求められるだけでなく、動作温度における高いTMR比も必要とされる。正方晶Mn系合金は、飽和磁化が小さく、保磁力が大きく、垂直磁気異方性が大きく、ギルバート減衰係数が小さいため、p-MTJの電極材料として魅力的な垂直磁化材料の一つである。しかし、Mn系合金を強磁性電極として用いたp-MTJでは、FeCo間層を用いても室温で最大60%と小さなTMRしか示さない。本発表では、bcc-CoMn合金を中間層に用いたp-MTJとそのTMR特性を示すとともに、MnGa系p-MTJの最近の進展についても簡単に紹介する。