Search

Abstract During mid-Cretaceous Oceanic Anoxic Event 2, significant increase of atmospheric carbon dioxide concentrations from the eruption of the large igneous provinces is hypothesized to have induced a humid climate and an elevation in nutrient runoff from continents to the oceans, resulting in oxygen depletion in the ocean. However, hitherto there is limited insight into the driving factors of Oceanic Anoxic Event 2 from the Pacific and Asian continental margins, even though the former and the latter were the largest ocean and landmass at that time. Here, a multiproxy analysis for the Oceanic Anoxic Event 2 interval of the Yezo Group –deposited on northwestern Pacific along the active Asian continental margin– is interpretated to identify seven volcanic pulses, five of which may have elevated humidity, weathering intensity, and vegetational change in the eastern margin of Asia. Moreover, oxygen depletion occurred simultaneously in the northwest Pacific. Given that these environmental changes in the eastern margin of Asia were penecontemporaneous with the global carbon burial intervals during Oceanic Anoxic Event 2, the elevated nutrient supply from the Asian continental margin to the Pacific Ocean may have, in part, contributed to the worldwide depletion of oxygen of the ocean during Oceanic Anoxic Event 2.

Antiferromagnetic (AFM) materials have attracted attention for device applications due to the absence of the stray field and high-frequency response. To integrate AFM materials into magnetic devices, the understanding of the interfacial effect between AFM and ferromagnetic (FM) materials is required. In particular, magnetization dynamics and magnetic damping are critical phenomena to be elucidated since they govern magnetization switching, spin-wave propagation, etc. Although a conventional method for studying the interfacial effects is stacking materials, the approach may cause unfavorable factors. To get insight into the dynamic properties at the AFM and FM interfaces, we have focused on B2-ordered FeRh, showing the first-order phase transition from the AFM to FM states, since the coexistence of AFM and FM domains occurs during transitions, which is an ideal platform for studying interfacial effects. For this study, we have studied ferromagnetic resonance (FMR) of FeRh thin films during the AFM–FM phase transition as a function of temperature. From the FMR measurements, we characterize the temperature dependence of the effective Gilbert damping constant αeff. We find that αeff decreases with increasing temperature, indicating that the temperature variation of the effective Gilbert damping constant originates from the exchange interaction between the AFM and FM domains in the film and/or AFM domains as a spin sink.

Cobalt-nickel nanoparticles (Co-Ni-NPs) show promising electrochemical performance in oxygen and hydrogen evolution reactions (OER and HER) due to their physicochemical properties such as electronic configuration and great electrochemical stability. Therefore, developing new economically and environmentally friendly methods of synthesizing Co-Ni-NPs has become a practical requirement. Co-Ni-NPs were produced by employing the liquid-phase reduction method. Nickel and cobalt sulfate solutions in hydrazine monohydrate with various mixing ratios were used as raw materials. Nickel plays an important role in the nucleation process via increasing the reduction reaction rate throughout the formation of Co-Ni-NPs. Furthermore, the acceleration of the Co-Ni-NPs formation process may be attributed to the partial dissolution of Ni(OH)2 in the presence of N2H4 and/or citrate-anions and the formation of the Ni-N2H4 or Ni-Cit complexes in contrast to Co(OH)2.

Cobalt nanoparticles were produced by employing the liquid-phase reduction method and hydrazine. The effect of citric acid additives on the formation and growth mechanism of cobalt nanoparticles was investigated using polarization methods. The cobalt nanoparticles produced in 0.2 M cobalt sulfate and 5 M hydrazine at 298 K had a spherical shape with a diameter of 400 nm. The dendritic nanoparticles formed with the decreasing of hydrazine concentration at 298 K. On the other hand, dendritic large particles are confirmed at 353 K. It was confirmed that the reduction reaction progressed with the addition of citric acid, and a hexagonal close-packed (εCo) phase was formed.