On the evolution of antiferromagnetic nanodomains in NiO thin films: A LEEM study

Fractional order (1/2, 0) spots appear in the electron diffraction from NiO/Ag(001) films due to exchange scattering of low energy electrons by the antiferromagnetically ordered surface Ni moments. Utilizing these beams, imaging of the nanosized surface magnetic domains were carried out employing the high spatial resolution (similar to 10 nm) of the Low Energy Electron Microscopy (LEEM) in the dark-field (DF) mode. While selected through a contrast aperture, the four magnetic reflections produced by the p(2 x 2) anti-ferromagnetic sub-lattice lead to the visualization of the different magnetic twin domains. The intensity variations of different twin domains were measured as a function of electron beam energies via domain resolved LEEM I-V plots. The surface Neel temperatures (T-N) of the films were measured using the temperature dependence of these half-order spot intensities. Detailed morphological studies of the size and shape of these nanodomains and their evolution as a function of the film thickness have been carried out with the help of pair-correlation function and fractal analysis. The size, shape and distribution of these magnetic domains are modified significantly by the strain relaxation mechanism beyond the critical film thickness. A method to estimate the relative domain sizes from a quantitative measure of the half-order spot intensities is manifested well below TN. (C) 2017 Elsevier B.V. All rights reserved.