2D correlations in the van der Waals ferromagnet CrBr3 using high frequency electron spin resonance spectroscopy

Abstract

Broadening the knowledge and understanding on the magnetic correlations in van der Waals layered magnets is critical in realizing their potential next-generation applications. In this study, we employ high frequency (240 GHz) electron spin resonance (ESR) spectroscopy on plate-like CrBr3 to gain insight into the magnetic interactions as a function of temperature (200 -4 K) and the angle of rotation θ. We find that the temperature dependence of the ESR linewidth is well described by the Ginzberg-Landau critical model as well as Berezinskii-Kosterlitz-Thouless (BKT) transition model, indicative of the presence of two-dimensional (2D) correlations. This suggests that the three-dimensional ferromagnet CrBr3, which has been described as an Ising or Heisenberg ferromagnet, could present 2D magnetic correlations and BKT-like behavior even in its bulk form; an observation that, to the best of our knowledge, has not been reported in the literature. Furthermore, our findings show that the resonance field follows a (3𝑐𝑜𝑠 2 θ − 1)-like angular dependence, while the linewidth follows a (3𝑐𝑜𝑠 2 θ − 1) 2 -like angular dependence. This observed angular dependence of the resonance field and linewidth further confirm an unanticipated 2D magnetic behavior in CrBr3. This behavior is likely due to the interaction of the external magnetic field applied during the ESR experiment that allows for the mediation of long-range vortex-like correlations between the spin clusters that may have formed due to magnetic phase separation. This study demonstrates the significance of employing spin sensitive techniques such as ESR to better understand the magnetic correlations in similar van der Waals magnets.

Evolution of the spin dynamics in the van der Waals system $M_{\text{2}}$P$_{\text{2}}$S$_{\text{6}}$ ($\boldsymbol{M}_{\text{2}}$ = Mn$_{\text{2}}$, MnNi, Ni$_{\text{2}}$) series probed by electron spin resonance spectroscopy

“…The ESR method, enabling a direct access to the electronic spin system, was recently successfully applied for studies of several magnetic van der Waals compounds providing important insights into the peculiarities of their spin dynamics. [4,[20][21][22][23][24][25][26][27][28][29][30][31]. Here we show that signatures of the low dimensionality, seen in the characteristic angular dependence of the ESR linewidth, are present only in the Mn 2 P 2 S 6 compound.…”