Electron-spin-resonance studies of the ferrimagnetic semiconductor FeCr2S4

Electron-spin-resonance (ESR) measurements have been performed on FeCr₂S₄ single crystals in the temperature range 4.2-200 K. On decreasing temperature, the resonance lines strongly shift to low fields for the easy magnetization direction, <100>, and to high fields for the hard directions, <110> and <111>. In the hard directions additional resonance modes appear below 125 K. The nonmonotonic behaviors of the ESR linewidth and intensity indicate substantial changes of the relaxation processes below 125 K, which correlates with the macroscopic dc magnetization and ac susceptibility data.