Kurokawa Yuichiro, Yamada Keisuke, Taniguchi Tomohiro, Horiike Shu, Tanaka Terumitsu, Yuasa Hiromi
Graduate School and Faculty of Information Science and Electrical Engineering, Kyushu University, Fukuoka, 819-0395, Japan.
Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Gifu, 501-1193, Japan.
Sci Rep. 2022 Jul 19;12(1):10849. doi: 10.1038/s41598-022-15014-y.
Recent increased development interest in millimeter-wave oscillator devices has necessitated realization of small oscillators with high frequency, wide frequency tunability, and room-temperature operation. Spin-torque oscillators (STOs) are fascinating candidates for such applications because of their nanometer size and suitability for room-temperature operation. However, their oscillation frequency and tunable range are limited to the order of 100 MHz-10 GHz. Here, we propose use of bilinear (J) and biquadratic (J) interlayer exchange couplings between ferromagnets in STOs to overcome these problems. The bilinear coupling contributes to oscillation frequency enhancement, whereas the biquadratic coupling facilitates frequency tunability via a current. Using micromagnetic simulation with parameters estimated from a material with small saturation magnetization, for J = 0 and J = - 1.0 mJ/m, respectively, we find that the STO exhibits high frequency from 23 to 576 GHz and that its tunability reaches 61 GHz/(10 A/m) for current densities of - 0.5 to - 9.5 × 10 A/m. An analytical theory based on the macrospin model is also developed, which exhibits good quantitative agreement with the micromagnetic simulations. These results introduce new possibilities for spintronics applications in high-frequency devices such as next-generation mobile communications.
最近，对毫米波振荡器器件的开发兴趣不断增加，因此需要实现具有高频、宽频率可调性和室温工作特性的小型振荡器。自旋扭矩振荡器（STO）因其纳米尺寸和适合室温工作而成为这类应用的理想候选者。然而，它们的振荡频率和可调范围限制在100MHz至10GHz的量级。在此，我们提出利用STO中铁磁体之间的双线性（J）和双二次（J）层间交换耦合来克服这些问题。双线性耦合有助于提高振荡频率，而双二次耦合则通过电流促进频率可调性。使用根据具有小饱和磁化强度的材料估算的参数进行微磁模拟，对于J = 0和J = -1.0 mJ/m，我们发现STO的频率范围为23至576GHz，并且对于-0.5至-9.5×10 A/m的电流密度，其可调性达到61GHz/（10 A/m）。还开发了一种基于宏观自旋模型的解析理论，该理论与微磁模拟具有良好的定量一致性。这些结果为自旋电子学在下一代移动通信等高频器件中的应用带来了新的可能性。
