  Nonvolatile spintronics-based devices that utilize electron spin both to
store and transport information face a great challenge when scaled to nano
dimensions due to loss of thermal stability and stray field induced disturbance
in closely packed magnetic bits. The potential replacement of ferromagnetic
materials with antiferromagnets may overcome some of these issues owing to the
superior robustness of sublattice spin orientations to magnetic field
disturbance as long as theyare kept well below the N\'eel temperature, which is
hard to measure with conventional methods, especially in the ultrathin limit.
In this work, we have employed spin pumping from a soft ferromagnetic NiFe
layer into widely used ultrathin metallic antiferromagnet Ir20Mn80, FeMn, PtMn,
PdMn or NiMn with thicknesses in the 0.7-3 nm range, as a probe to detect
damping enhancement during magnetic phase transitions. Independent measurements
of the blocking temperature with magnetometry reveal that temperature dependent
shifts in the resonance peaks can also be used to measure the blocking
temperature, allowing the analysis of the correlation between the N\'eel and
blocking temperatures in trilayers with permalloy and antiferromagnetic layer
separated by a 3 nm thick spacer layer. The thickness dependent
characterization of thermal stability in antiferromagnets provides a key
element for scalable and ultrafast antiferromagnetic spintronics.
