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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.

Many recent studies have explored the response of magnetic systems to circularly polarised light. To achieve this, typically experiments use a birefringent crystal. Here, Yang et al show that any small error in the alignment of the crystal can result in a beam shift, and this shift can lead to spurious signals similar yet unrelated to the electron spin.

All-optical ferromagnetic resonance (AO-FMR) is a powerful tool for the local detection of micromagnetic parameters, such as magnetic anisotropy, Gilbert damping or spin stiffness. In this work we demonstrate that the AO-FMR method can be used in thin films of yttrium iron garnet (YIG) if a metallic capping layer (Au, Pt) is deposited on top of the film. Magnetization precession is triggered by heating of the metallic layer with femtosecond laser pulses. The heat pulse modifies the magneto-crystalline anisotropy of the YIG film and shifts the quasi-equilibrium orientation of the magnetization, which results in precessional magnetization dynamics. The laser-induced magnetization precession corresponds to a uniform (Kittel) magnon mode, with the precession frequency determined by the magnetic anisotropy of the material as well as the external magnetic field, and the damping time set by a Gilbert damping parameter. The AO-FMR method thus enables measuring local magnetic properties, with a resolution given by the laser spot size.

Abstract Phases with spontaneous time-reversal ( $${{{{{{{\mathcal{T}}}}}}}}$$ T ) symmetry breaking are sought after for their anomalous physical properties, low-dissipation electronic and spin responses, and information-technology applications. Recently predicted altermagnetic phase features an unconventional and attractive combination of a strong $${{{{{{{\mathcal{T}}}}}}}}$$ T -symmetry breaking in the electronic structure and a zero or only weak-relativistic magnetization. In this work, we experimentally observe the anomalous Hall effect, a prominent representative of the $${{{{{{{\mathcal{T}}}}}}}}$$ T -symmetry breaking responses, in the absence of an external magnetic field in epitaxial thin-film Mn5Si3 with a vanishingly small net magnetic moment. By symmetry analysis and first-principles calculations we demonstrate that the unconventional d-wave altermagnetic phase is consistent with the experimental structural and magnetic characterization of the Mn5Si3 epilayers, and that the theoretical anomalous Hall conductivity generated by the phase is sizable, in agreement with experiment. An analogy with unconventional d-wave superconductivity suggests that our identification of a candidate of unconventional d-wave altermagnetism points towards a new chapter of research and applications of magnetic phases.