Cooperative multiscale aging in a ferromagnet/antiferromagnet bilayer

Anisotropic magnetoresistance measurements show that the magnetization state in epitaxial Ni80Fe20/Fe50Mn50 bilayers exhibits aging over a wide range of temperatures and magnetic fields. The observed power-law time dependence indicates that aging is characterized by a wide range of activation time scales. Aging characteristics are also inconsistent with a superposition of independent activation barriers expected for Arrhenius-type relaxation. The observed effects indicate a fundamental connection with the critical phenomena in complex condensed matter systems.