Epitaxial NiCo2O4 film as an emergent spintronic material: Magnetism and transport properties

Abstract

The ferrimagnetic inverse spinel NiCo2O4 has attracted extensive research interest for its versatile electrochemical properties, robust magnetic order, high conductivity, and fast spin dynamics, as well as its highly tunable nature due to the closely coupled charge, spin, orbital, lattice, and defect effects. Single-crystalline epitaxial thin films of NiCo2O4 present a model system for elucidating the intrinsic physical properties and strong tunability, which are not viable in bulk single crystals. In this Perspective, we discuss the recent advances in epitaxial NiCo2O4 thin films, focusing on understanding its unusual magnetic and transport properties in light of crystal structure and electronic structure. The perpendicular magnetic anisotropy in compressively strained NiCo2O4 films is explained by considering the strong spin–lattice coupling, particularly on Co ions. The prominent effect of growth conditions reveals the complex interplay between the crystal structure, cation stoichiometry, valence state, and site occupancy. NiCo2O4 thin films also exhibit various magnetotransport anomalies, including linear magnetoresistance and sign change in anomalous Hall effect, which illustrate the competing effects of band-intrinsic Berry phase and impurity scattering. The fundamental understanding of these phenomena will facilitate the functional design of NiCo2O4 thin films for nanoscale spintronic applications.

The first structural, morphological and magnetic property studies on spinel nickel cobaltite nanoparticles synthesized from non-standard reagents

“…These interactions are impacted by the types of cations and their distribution in the A and B sites. 70 In fact, the largest exchange interaction in NiCo 2 O 4 spinel nanomaterials exists between the edge-sharing B sites, because we have a cation-O-cation bond angle of 901 that matches with the ferromagnetic interactions, generally lower than the antiferromagnetic interactions produced by the strongest exchange interaction. This interaction exists between the corner-sharing A and B sites, where the cation-O-cation bond angle is 1251.…”

“…The magnetic behavior of the spinel materials is affected by many factors such as the high magnetic moment of some cations, doped elements in the spinel structure and magnetic interactions between cations. 70 In the A x B 3− x O 4 magnetic spinel, there exist three types of exchange magnetic interactions between cations in the structure, namely A–A, B–B and the stronger A–B exchange interactions. These interactions are impacted by the types of cations and their distribution in the A and B sites.…”

“…Since the magnetic cobalt and nickel cations occupy the corner–sharing B and A sites, respectively, their different magnetic moments are expected to be antiparallel, resulting in ferrimagnetism. 42,70,71…”

“…Since the magnetic cobalt and nickel cations occupy the corner-sharing B and A sites, respectively, their different magnetic moments are expected to be antiparallel, resulting in ferrimagnetism. 42,70,71 The magnetization measurements of the elaborated NiCo 2 O 4 spinel nanoparticles at 300 1C were performed by applying a magnetic field from À10 to 10 kOe at room temperature. The magnetic hysteresis loop of NiCo 2 O 4 spinel is shown in Fig.…”

Influence of Oxygen Plasma on the Growth and Stability of Epitaxial NiCo2O4 Ultrathin Films on Various Substrates

“…Moreover, the tetrahedral sites could be occupied with Co 2+ and Co 3+ cations, while the octahedral sites are occupied with Ni 2+ , Ni 3+ and Co 3+ cation. A coupling between conductivity and cationic distribution (the degree of inversion defined as a fraction of Co 3+ cations on tetrahedral sites) dependent on synthesis conditions has been reported [ 4 ], making p-type conducting NCO a promising candidate for future spintronic applications [ 4 , 6 , 7 , 8 , 9 ]. Further potential applications for NCO are, for example, infrared transparent electrodes [ 10 , 11 ] or supercapacitors [ 12 , 13 ] for energy storage [ 14 , 15 , 16 ].…”