Magneto-ionic Enhancement of Exchange Bias in MnN/CoFe*

The magneto-ionic effect has shown promise as an effective approach to control magnetic properties through controlled motion of ionic species, which can be tailored under an applied electric field.¹ For example, magneto-ionic control of exchange bias may lead to reduction in energy costs and the development of novel devices.² We have investigated nitrogen-ion induced exchange bias effects in MnN/CoFe films grown on a Ta seed layer.³ Upon field cooling across the Néel temperature of MnN, a significant exchange bias of ~ 620 Oe is induced. Polarized neutron reflectometry (PNR) shows that nitrogen migrates from MnN into the Ta, the latter acts as a nitrogen getter. Subsequently nitrogen is driven from the Ta back into MnN by applying an electric field, confirmed by PNR. The increase in nitrogen content in MnN leads to an increase in exchange bias of ~ 30 Oe (5%). Preliminary studies also show that this electric field effect is reversible. These results indicate a sensitive nitrogen-ion based magneto-ionic approach to tuning exchange bias.

¹ U. Bauer, et at., Nat. Mater. 14, 174 (2015).
² D. A. Gilbert, et al., Nat. Commun. 7, 11050 (2016).
³ P. Quarterman, et al., Phys. Rev. Mater. 3, 064413 (2019).