A magnetically driven magnetostrictive sample, which is used as the sensing element in a fiber‐optic magnetometer, is known to exhibit strain bifurcations. Standard techniques for fiber‐optic magnetostrictive magnetometers employ demodulation at a carrier frequency &ohgr;cbut, typically, the resolution is limited by 1/fnoise around &ohgr;c. We present a novel technique for the detection of low‐frequency magnetic signals which employs the frequency associated with a period doubling bifurcation &ohgr;c/2, and which avoids upconverted 1/fnoise near &ohgr;c. The signal‐to‐noise ratio of low‐frequency magnetic signals near &ohgr;c/2 remains flat in the range 0.025–10 Hz, with a resolution of 5 nT/&sqrt;Hz for a sensor using only 5 mm of fiber, limited by the phase noise of the fiber interferometer.