Formation and Microstructural Evolution of Antiphase Domain Boundaries in NiCo ₂ O ₄ /MgAl ₂ O ₄ (001) Thin Films Regulated by Growth Pressure

ABSTRACT In this paper, the microstructural evolution of NiCo 2 O 4 (NCO) thin films epitaxially grown on MgAl 2 O 4 ‐(001) (MAO) substrates under three different pressures (10, 20, and 75 Pa) was investigated at the atomic scale via spherical aberration‐corrected transmission electron microscopy. It is found that growth pressure significantly regulates the formation of internal defects in the films: under a low pressure of 10 Pa, a /4[110]‐antiphase domain boundary (APB) were formed near the interface; at 20 Pa, two non‐overlapping a /4[101]‐APB were generated inside the films to release the misfit stress between the film and the substrate, and atomic structure analysis shows that both types of APBs are expected to exhibit antiferromagnetism; under a high pressure of 75 Pa, no APB was formed in the film, but a phase transition from the spinel structure to the rock salt structure was observed, and the involved atomic displacement process was analyzed. This study clearly reveals that regulating growth pressure is an effective approach to control the formation and structural evolution of APBs in NCO/MAO thin films.