16:00 〜 18:00
▲ [14p-P10-41] Inverse Tunnel Magnetocapacitance in Fe/Al-oxide/Fe3O4
キーワード：Magnetic tunnel junction, Magnetocapacitance, AC characteristics
Magnetocapacitance (MC) effect in spintronic devices has attracted much interest due to their fascinating spin-based phenomena, such as spin capacitance, frequency-dependent spin transport, and potential applications as sensitive magnetic sensors, high-frequency devices, and energy storage materials. The MC effect has been observed in magnetic tunnel junctions (MTJs), molecular spin valve devices, magnetic nanogranular films, and magnetic single-electron transistors. The MC in MTJs is generally referred to as tunnel magnetocapacitance (TMC). In normal TMC, the capacitance CP is high for the parallel (P) configuration of the magnetization vectors in both ferromagnetic layers adjacent to the barrier, and CAP is low for the antiparallel (AP) configuration. In this current work, we report an inverse TMC effect (i.e., CP < CAP) for the first time in Fe/AlOx/Fe3O4 MTJs.
We prepared the device structure by using a molecular beam epitaxy system with a base pressure of 10–8 Pa. The MTJ stack consists of MgO(110)/MgO(20 nm)/NiO(5 nm)/Fe3O4(60 nm)/AlOx(2–4 nm)/Fe(10 nm)/Au(30 nm). We patterned the MTJ structures with a junction area of 10×10 μm2 by using standard photolithography with Ar ion-milling and SiO2 insulation overlayer. The magnitude of the inverse TMC reaches up to 11.4% at room temperature and the robustness of spin polarization is revealed in the bias dependence of the inverse TMC. 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 Zhang formula and parabolic barrier approximation) and spin-dependent drift-diffusion model. Furthermore, our theoretical calculations predict that the inverse TMC effect could potentially reach 150% in MTJs with a positive and negative spin polarization of 65% and –42%, respectively. These theoretical and experimental findings provide a new insight into both static and dynamic spin-dependent transports. They will open broader opportunities for device applications, such as magnetic logic circuits and multi-valued memory devices.
We prepared the device structure by using a molecular beam epitaxy system with a base pressure of 10–8 Pa. The MTJ stack consists of MgO(110)/MgO(20 nm)/NiO(5 nm)/Fe3O4(60 nm)/AlOx(2–4 nm)/Fe(10 nm)/Au(30 nm). We patterned the MTJ structures with a junction area of 10×10 μm2 by using standard photolithography with Ar ion-milling and SiO2 insulation overlayer. The magnitude of the inverse TMC reaches up to 11.4% at room temperature and the robustness of spin polarization is revealed in the bias dependence of the inverse TMC. 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 Zhang formula and parabolic barrier approximation) and spin-dependent drift-diffusion model. Furthermore, our theoretical calculations predict that the inverse TMC effect could potentially reach 150% in MTJs with a positive and negative spin polarization of 65% and –42%, respectively. These theoretical and experimental findings provide a new insight into both static and dynamic spin-dependent transports. They will open broader opportunities for device applications, such as magnetic logic circuits and multi-valued memory devices.