Investigation of High-Frequency Electron Paramagnetic Resonance in the Kagome-Lattice YMn6Sn6 Crystal

Kagome magnetic crystals received a great deal of research attention in the recent past for their intriguing magnetic properties. Recently, YMn₆Sn₆ has been shown to exhibit several nontrivial magnetic phases, and the origin remains elusive. In this work, we employed very high-frequency electron paramagnetic resonance (VHF-EPR) spectroscopy to investigate the local microscopic magnetic interactions of Mn ions in the Kagome Crystal YMn₆Sn₆ (YMnSn) to better understand the new observed magnetic phases. Particularly, we studied the temperature-dependent EPR behavior at the microwave frequency (ν = 120, 240, and 300 GHz). We also investigated the EPR spectral behavior above room temperature on YMnSn single crystals, where the magnetic field was applied within both the in-plane and out-of-plane orientations of the sample layers, to broaden our knowledge and understanding of the magnetic interactions and properties of this compound. In addition, we have performed EPR at v = 120 GHz to study the angular dependence of the resonance field, g-value and linewidth at the angle of rotation θ (radians). We find that the linewidth of YMnSn follows a (3cos²�� − 1)²-like angular dependence whilst the g-value and resonance field follow a (3cos²�� − 1)- like angular dependence which reveals the “W-shape and U-shape” of the linewidth and g-values respectively. This behavior shows the presence of spin correlations which is likely because of the interaction of the external magnetic field applied during the EPR experiment. The temperature dependencies of signal behavior, signal width, and g-values were tracked to study the magnetic phase transitions in the YMnSn compound as a function of temperature (5 – 350 K). Our frequency dependence EPR measurements also show that as the frequency increases, the resolution of the EPR spectrum improves, which means that at 240 GHz and 300 GHz, we can resolve finer details in the spectrum compared to 120 GHz.