LI LI and colleagues at university of science and technology of China, in collaboration with Zhaorong Yang at institute of solid state physics, have successfully synthesized single crystals K_xFe_2-ySe_{2 -z}S_z (z = 0, 0.4) with the superconducting transition temperatures Tc^onset of 31.3 K and 32.8 K, respectively. In addition to conventional measurements of the structural, magnetic and electrical-transport properties, they further performed electron spin resonance (ESR) measurements to study the micro-magnetism of the K_xFe_2-ySe₂ and K_xFe_2-ySe1.6S0_.4 single crystals. The ESR results have been well discussed by correlating with recent neutron diffraction and Raman scattering results. Detailed investigation on the evolution of ESR spectrum reveals that the PM component in system decreases with temperature and transforms into AFM phase entirely near 2Tc. Moreover, the variation of resonance field with decreasing temperature for K_xFe_2-ySe₁.₆S₀.₄ implies that substitution of S for Se induces local weak ferromagnetism in the parent AFM background. These results provide extra evidence for the coexistence of superconductivity with magnetism in addition to SR, neutron diffraction, Raman-scattering, and M？ssbauer studies. This work has been published in Physical Review B [Physical Review B 84, 174501(2011)].