  The precession of magnon pseudospin about the equilibrium pseudofield, the
latter capturing the nature of magnonic eigen-excitations in an
antiferromagnet, gives rise to the magnon Hanle effect. Its realization via
electrically injected and detected spin transport in an antiferromagnetic
insulator demonstrates its high potential for devices and as a convenient probe
for magnon eigenmodes and the underlying spin interactions in the
antiferromagnet. Here, we observe a nonreciprocity in the Hanle signal measured
in hematite using two spatially separated platinum electrodes as spin
injector/detector. Interchanging their roles was found to alter the detected
magnon spin signal. The recorded difference depends on the applied magnetic
field and reverses sign when the signal passes its nominal maximum at the
so-called compensation field. We explain these observations in terms of a spin
transport direction-dependent pseudofield. The latter leads to a
nonreciprocity, which is found to be controllable via the applied magnetic
field. The observed nonreciprocal response in the readily available hematite
films opens interesting opportunities for realizing exotic physics predicted so
far only for antiferromagnets with special crystal structures.

Mesoscale and Nanoscale Physics;Materials Science