Transport Anomaly in Perpendicular Magnetic Anisotropic NiCo₂O₄ Thin Films with Column-like Phase Separation

Abstract

Inverse spinel oxide NiCo 2 O 4 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 NiCo 2 O 4 films have been deposited on MgAl 2 O 4 substrates via pulsed laser deposition. The nanocolumn NiCo 2 O 4 is identified as an ideal inverse spinel NiCo 2 O 4 structure and an imperfect inverse spinel structure with Co vacancies at tetrahedral sites. Compared to the usual single-phase NiCo 2 O 4 film, a 20-fold enhancement of magnetoresistance (MRR = 6% at 10 K and 3 T) is observed in the semiconducting NiCo 2 O 4 film with columnlike phase separation, accompanying a 25-fold increase in coercivity (H C = 18.1 kOe at 10 K) due to the strong interfacial interaction at the vertical phase boundaries. The nanocolumn NiCo 2 O 4 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.

Underlying Mechanisms and Tunability of the Anomalous Hall Effect in NiCo2O4 Films with Robust Perpendicular Magnetic Anisotropy

“…[11,37] The MR characteristics reported for different types of single phase NCO films is consistent with the behavior revealed by Figure 3c. [14,36] In the case of a pronounced phase coexistence, in contrast, MR(𝜎 xx ) with a negative slope…”

Spin reorientation in tetragonally distorted spinel oxide NiCo$_2$O$_4$ epitaxial films

“…In particular, a large tunnel magnetoresistance effect has recently been reported in magnetic tunnel junctions fabricated using NCO electrodes, supporting the half-metallic nature [4,7,8]. In addition, NCO(001) films grown on MgAl 2 O 4 (MAO) substrates exhibited perpendicular magnetic anisotropy (PMA) [9][10][11][12] of K eff u ≈ 0.3 MJ/m 3 at room temperature. The fact that both the half-metallicity and PMA are realized at once indicates that the NCO films possess good potential for application in spintronic devices.…”

Low-temperature cluster spin glass transition in the single-domain NiCr2O4 nanoparticles

“…Studies of nanomagnetism usually explore interesting phenomena in magnetic nanoparticles when compared to its fundamental bulk properties [1]. For example, exotic magnetic states with potential phenomena were reported for frustrated magnetic systems in nanoparticles form and often attributed to finite size effects [2][3][4].…”