  We demonstrate theoretically that in a spintronic diode (SD), having a free
magnetic layer with perpendicular magnetic anisotropy of the first and second
order and no external bias magnetic field, the out-of-plane regime of
magnetization precession can be excited by sufficiently large (exceeding a
certain threshold) RF signals with the frequencies <~250 MHz. We also show that
such a device can operate as a broadband energy harvester capable of converting
incident RF power into a DC power with the conversion efficiency of ~5%. The
developed analytical theory of the bias-free SD operation can be used for the
optimization of high-efficiency RF detectors and energy harvesters based on
SDs.
