Magnetic field observation device and magnetic field observation method

A magnetic field observation method of observing a stray magnetic field from a magnetic material specimen, the magnetic field observation method comprising:

• a scanning step of arranging a probe that undergoes magnetization reversal more easily than the magnetic material specimen on the magnetic material specimen such that it is possible to excite the probe and simultaneously make a magnetic moment of the probe periodically undergo magnetization reversal, and of scanning a surface of the magnetic material specimen with the probe while applying to the probe an alternating magnetic field having such a magnitude as not to make the magnetic material specimen undergo magnetization reversal;
• and
• a modulation measurement step of applying to the probe a force whose intensity is periodically changed by an alternating force caused by a magnetic interaction between magnetization of the probe and magnetization of the magnetic material specimen where a direction of magnetization of the probe is periodically changed by the alternating magnetic field applied by the alternating magnetic field generation mechanism, of periodically changing an apparent spring constant of the probe with the periodic force and of measuring a degree of periodical frequency modulation of oscillation of the probe caused by periodical change of the spring constant by frequency demodulation or by measuring an intensity of one sideband wave spectrum among sideband wave spectrums generated by the frequency modulation,
• wherein, in the scanning step, a product of an intensity of a residual magnetic pole of a tip of the probe that is not changed even by application of the alternating magnetic field from the alternating magnetic field generation mechanism and a gradient of the alternating magnetic field applied from the alternating magnetic field generation mechanism to the probe is smaller than a product of an intensity of a magnetic pole of the tip of the probe that is changed by the application of the alternating magnetic field from the alternating magnetic field generation mechanism and a gradient of a magnetic field applied from the magnetic material specimen to the probe.