  Magnetic and magneto-transport properties of manganese nitride films grown by
molecular beam epitaxy have been investigated. Due to the mixed ferrimagnetic
(FI) phase (${\epsilon}$-phase with TFI ~ 738 K) and the antiferromagnetic
phase (${\zeta}$-phase with TN ~ 273 K), we observe magnetization hysteresis
loops with non-zero exchange bias below TN, reaching ~ 0.22 T at 5 K. This
indicates that noncollinear spins exist at the interfaces between two phases,
creating a competition between interfacial Dzyaloshinskii-Moriya (DM) and
exchange interactions. Strikingly, in addition to the normal Hall effect by
Lorentz force and anomalous Hall effect by magnetization, we observe new
contribution namely topological Hall effect below 75 K. This verifies the
existence of topological spin texture, which is the consequence of competing
interactions controlled by both applied field and temperature. Our work
demonstrates that spintronic devices may be fabricated exploiting rich magnetic
properties of different phases.
