Manipulate the magnetic and electronic states in NiCo₂O₄ films through protonation

Element doping and substitution have been widely used for the engineering of the electronic structure and macroscopic magnetic properties of various materials. However, traditional doping process does not allow further optimization after preparation of the samples. Hydrogen annealing-induced protonation has emerged as a powerful method for the efficient control of uniaxial lattice expansion to modulate the physics properties of the otherwise inaccessible novel correlated phases in oxide thin-films. Here, we report the modulation of the magnetic moment, magneto-transport and electrical-transport in inverse-spinel NiCo₂O₄ (NCO) by protonation. Strong dependence of saturation magnetic moment and electrical conduction on deposition temperature and proton doping parameters has been systematically investigated. The magnetoresistance ratio of the protonated NCO could be increased by 400% by engineering of the doping condition and thus the phase configuration. These findings indicate that protonation is one effective strategy for regulation and optimization of NCO-based magnetic and electric devices.