Features of $$\textrm{EuFe}_2\textrm{As}_2$$ Magnetic Structure Revealed by ESR

Magnetic state of the $$\textrm{EuFe}_2\textrm{As}_2$$ single crystal was investigated by electron spin resonance (ESR). The ESR spectra of europium ions were registered in the temperature range from 250 to 4 K. To study the anisotropy, the in-plane angular dependences were investigated at temperatures of 15 K upon rotating a crystal around the c-axis. The data analysis shows that $$\textrm{EuFe}_2\textrm{As}_2$$ is an antiferromagnet with an easy anisotropy plane. Moreover, the second-order easy magnetization axis is observed for each of the two types of magnetic domains related with structural twins arising from the tetragonal-to-orthorhombic crystal lattice transition.