Enhanced nitrogen-based magneto-ionic manipulation of Exchange Bias in Co/CoMnN heterostructures

In the framework of nanomagnetism and spintronics, electric field control of exchange-biased heterostructures emerges as a low energy consumption approach, implemented through several methodologies such as multiferroics, carrier doping, and magneto-ionics. Specifically, nitrogen-based magneto-ionics stands out due to its fast ionic motion and CMOS compatibility. Indeed, recent research in a Ta/CoFe(FM)/MnN(AFM)/Ta system showcases the potential of nitrogen-based magneto-ionics in the field of exchange-biased heterostructures, enhancing the exchange bias field by 5% at 300 K and 19% at 10 K. In the present work, the MnN(AFM) layer is gradually doped with increasing amounts of Co. We anticipate a decrease in the Mn-N bonding energy due to the addition, therefore increasing the amount of nitrogen that diffuses throughout the structure, in a manner complementary to what occurs in CoN structures when doped with small amounts of Mn. A series of Ta/Co(FM)/CoxMn1-xN(AFM)/Ta samples with Co at% (x) ranging from 0 to 24% reveals significant exchange bias up to 10% Co. Understanding how nitrogen relocates after field cooling (FC) the samples and treating them with an electric field (VC) would enlighten the mechanisms behind the trend observed by magnetometry: as Co at.% (x) content increases, so does the exchange bias relative change between the FC state and after the VC. By using PNR, we want to track the nitrogen depth-dependent distribution in our heterostructures.