トンネル磁気キャパシタンス効果の原理と新たな展開

抄録

Magnetocapacitance (MC) effect has attracted much attention due to the fascinating spin phenomena, such as spin capacitance, frequency-dependent spin transport and potential applications as highly-sensitive magnetic sensors, high-frequency devices and energy storage materials. The MC effect observed in magnetic tunneling systems is generally referred to as tunnel magnetocapacitance (TMC). A normal TMC effect exhibits a higher capacitance when spins in the electrodes are parallel to each other and a lower capacitance when spins are antiparallel. Here we report an inverse tunnel magnetocapacitance (iTMC) effect, which was recently observed in Fe/AlO_x/Fe₃O₄ magnetic tunnel junctions (MTJs). The iTMC reaches up to 11.4% at room temperature and the robustness of spin polarization is revealed in the bias dependence of the iTMC. Excellent agreement between theory and experiment is achieved for the entire applied frequency range and the wide bipolar bias regions using Debye-Fröhlich model, combined with the Zhang formula and parabolic barrier approximation, and spin-dependent drift-diffusion model. These theoretical and experimental findings provide a new insight into both static and dynamic spin-dependent transports.