Terahertz Probing of Anisotropic Conductivity and Morphology of CuMnAs Epitaxial Thin Films

Abstract

Antiferromagnetic CuMnAs thin films have attracted attention since the discovery of the manipulation of their magnetic structure via electrical, optical, and terahertz pulses, enabling convenient approaches for switching between magnetoresistive states of the film for information storage. However, the magnetic structure and, thus, the efficiency of the manipulation can be affected by the film morphology and growth defects. In this study, the properties of CuMnAs thin films are investigated by probing the asymmetrical growth‐related uniaxial anisotropy of electric conductivity by contact‐free terahertz transmission spectroscopy. It is shown that the terahertz measurements conveniently detect the conductivity anisotropy that is consistent with conventional DC Hall‐bar measurements. Moreover, the terahertz technique allows for considerably finer determination of anisotropy axes, and it is less sensitive to the local film degradation. Thanks to the averaging over a large detection area, the THz probing also allows an analysis of strongly non‐uniform thin films. Using scanning electron and near‐field terahertz microscopies, the observed anisotropic conductivity of CuMnAs is related to the elongation and orientation of growth defects, which both originate in the anisotropic growth of the films. In addition, control over the morphology of defects is demonstrated by using vicinal substrates.