Highly sensitive microwave devices that are operational at room temperature are important for high-speed multiplex telecommunications. Quantum devices such as superconducting bolometers possess high performance but work only at low temperature. On the other hand, semiconductor devices, although enabling high-speed operation at room temperature, have poor signal-to-noise ratios. In this regard, the demonstration of a diode based on spin-torque-induced ferromagnetic resonance between nanomagnets represented a promising development , even though the rectification output was too small for applications (1.4 mV/mW). Many efforts, such as control of magnetic field direction , the use of voltage torque and stochastic resonance, have significantly enhanced the sensitivity; nevertheless, the room-temperature sensitivity of MTJs remains far lower than that of semiconductors. Here we show that by applying DC bias currents to nanomagnets while precisely controlling their magnetization-potential profiles, a much greater radiofrequency detection sensitivity of 12,000 mV/mW is achievable at room temperature , exceeding that of semiconductor Schottky diode detectors (3,800 mV/mW). The analysis based on a macro-spin model revealed that the increase is caused by the rotation of the precession axis that depends on the input RF power. This rotation, a type of nonlinear FMR, results in a change in resistance and affords the high sensitivity to the MTJs. In addition, it is found that this non-linear effect enhances signals more than noise as the size of the magnets decreases.  A. A. Tulapurkar et al., Nature 438 (2005), 339.  S. Miwa et al., Nature Mater. (2013) doi: 10.1038/nmat3778.