  We have reinvestigated the magnetic properties of the classical metallic
helimagnet MnP by magnetization and neutron scattering experiments. Our neutron
scattering results indicate that the previously reported magnetic structure in
the low-temperature (LT) helimagnetic phase (T < 47K) should be modified to an
alternately tilted helimagnetic structure pro- duced by the
Dzyaloshinsky-Moriya interaction. In the intermediate temperature (IT) range
between the LT helimagnetic phase and the high-temperature (HT) ferromagnetic
phase along the c-axis, 47K < T < 282K, we have found a weak ferromagnetic
behavior along the b-axis. Surprisingly, the IT weak ferromagnetic phase has
two different states, namely, the large magnetization (LM) and small
magnetization (SM) states. The SM state emerges with cooling from the
paramagnetic phase above 292 K via the HT ferromagnetic phase and LM state
emerges with warming from the LT helimagnetic phase. The weak ferromagnetism
along the b-axis and the unusual temperature hysteresis in the IT phase can be
understood by assuming a spontaneous formation of the stripe structure
consisting of alternately arranged HT ferromagnetic and LT helimagnetic
domains.
