  The magnetic properties of thin-film multilayers [Fe/Py]/FeMn/Py are
investigated as a function of temperature and thickness of the
antiferromagnetic FeMn spacer using SQUID magnetometry. The observed behavior
differs substantially for the structures with 6-nm and 15-nm FeMn spacers.
While the 15-nm-FeMn structure exhibits exchange pinning of both ferromagnetic
layers in the entire measurement temperature interval from 5 to 300 K, the
6-nm-FeMn structure becomes exchange de-pinned in the vicinity of room
temperature. The de-pinned state is characterized by a single hysteresis loop
centered around zero field and having enhanced magnetic coercivity. The
observed properties are explained in terms of finite-size effects and possibly
ferromagnetic interlayer coupling through the thin antiferromagnetic spacer.
