Transport Anomaly in Perpendicular Magnetic Anisotropic NiCo<sub>2</sub>O<sub>4</sub> Thin Films with Column-like Phase Separation
Mingzhu Xue, Xuegang Chen, Shilei Ding, Zhongyu Liang, Yuxuan Peng, Xin Li, Liang Zha, Wenyun Yang, Jingzhi Han, Shunquan Liu, Honglin Du, Changsheng Wang, Jinbo Yang
Abstract
Inverse spinel oxide NiCo2O4 is an excellent prototype to explore complex energy landscapes among exchange interactions, crystal field effects, and chemical/lattice disorders. In this work, periodic phase-separated nanocolumn NiCo2O4 films have been deposited on MgAl2O4 substrates via pulsed laser deposition. The nanocolumn NiCo2O4 is identified as an ideal inverse spinel NiCo2O4 structure and an imperfect inverse spinel structure with Co vacancies at tetrahedral sites. Compared to the usual single-phase NiCo2O4 film, a 20-fold enhancement of magnetoresistance (MRR = 6% at 10 K and 3 T) is observed in the semiconducting NiCo2O4 film with column-like phase separation, accompanying a 25-fold increase in coercivity (HC = 18.1 kOe at 10 K) due to the strong interfacial interaction at the vertical phase boundaries. The nanocolumn NiCo2O4 also exhibits strong perpendicular magnetic anisotropy as well as a robust anomalous Hall effect (AHE) below the Curie temperature. In addition, a Hall resistance jump near the coercive field is observed, which is related to the domain rotation in the vicinity of the switching field. This study provides a phase-separated nanocolumn material with strong vertical coupling for designing artificial nanostructured spintronic devices.