biostudies-literatureKurokawa YOGAWA Science and Technology FoundationHattori Hokokai FoundationJapan Society for the Promotion of Science10849https://www.ebi.ac.uk/biostudies/studies/S-EPMC9296563biostudies-literatureUnknown12(1)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 (J₁) and biquadratic (J₂) 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 J₁ = 0 and J₂ =  - 1.0 mJ/m², respectively, we find that the STO exhibits high frequency from 23 to 576 GHz and that its tunability reaches 61 GHz/(10¹¹ A/m²) for current densities of - 0.5 to - 9.5 × 10¹¹ A/m². 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.Scientific reportsUltra-wide-band millimeter-wave generator using spin torque oscillator with strong interlayer exchange couplings.PMC9296563JP21K14487JP20K05255Yuasa HHoriike STanaka TKurokawa YTaniguchi TYamada KfalseUltra-wide-band millimeter-wave generator using spin torque oscillator with strong interlayer exchange couplings.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 (J₁) and biquadratic (J₂) 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 J₁ = 0 and J₂ =  - 1.0 mJ/m², respectively, we find that the STO exhibits high frequency from 23 to 576 GHz and that its tunability reaches 61 GHz/(10¹¹ A/m²) for current densities of - 0.5 to - 9.5 × 10¹¹ A/m². 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.2022-01-01T00:00:00Z2022 Jul2025-04-04T10:47:47.091Z2025-04-04T10:47:47.091ZS-EPMC92965633585402410.1038/s41598-022-15014-y