  We report on temperature-dependent soft X-ray absorption spectroscopy (XAS)
measurements utilizing linearly polarized synchrotron radiation to probe
magnetic phase transitions in iron-rich Fe1+yTe. X-ray magnetic linear
dichroism (XMLD) signals, which sense magnetic ordering processes at surfaces,
start to increase monotonically below the N\'eel temperature TN = 57 K. This
increase is due to a progressive bicollinear antiferromagnetic (AFM) alignment
of Fe spins of the monoclinic Fe1+yTe parent phase. This AFM alignment was
achieved by a [100]-oriented biasing field favoring a single-domain state
during cooling across TN. Our specific heat and magnetization measurements
confirm the bulk character of this AFM phase transition. On longer time scales,
however, we observe that the field-biased AFM state is highly unstable even at
the lowest temperature of T = 3 K. After switching off the biasing field, the
XMLD signal decays exponentially with a time constant {\tau} = 1506 s. The
initial XMLD signal is restored only upon repeating a cycle consisting of
heating and field-cooling through TN. We explain the time effect by a gradual
formation of a multi-domain state with 90 deg rotated AFM domains, promoted by
structural disorder, facilitating the motion of twin-domains. Significant
disorder in our Fe1+yTe sample is evident from our X-ray diffraction and
specific heat data. The stability of magnetic phases in Fe-chalcogenides is an
important material property, since the Fe(Te1-xSex) phase diagram shows
magnetism intimately connected with superconductivity.
