Electron paramagnetic resonance in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$S, ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se, and ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te

We present results of a systematic investigation of EPR in the Cd-based family of diluted magnetic semiconductors (${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$S, ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Se, and ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Te) over a wide range of temperature and Mn concentration. The dependence of the EPR linewidth on the anion of the host lattice is established. Specifically, we find that, at a fixed temperature and Mn concentration, the linewidth increases in the order of sulfide, selenide, and telluride. This trend holds over a wide range of sample composition and temperature. We also demonstrate that the general EPR behavior in all three alloys is identical: namely, the absorption line shape is Lorentzian in the paramagnetic region of the phase diagram, and broadens with increasing x and decreasing T. The Lorentzian-regime line shape is analyzed using the exchange-narrowing picture. The observed dependence of the EPR linewidth on the anion cannot be explained by dipolar broadening alone. We argue that the dominant anisotropic spin-spin interaction must be the anisotropic part of the exchange interaction, and speculate that the Dzyaloshinski-Moriya interaction may play a role. The exchange-narrowing theory is also used to examine the variation of the linewidth with sample composition and temperature. At very low temperatures, as the spin-glass transition is approached, the line shape deviates from Lorentzian behavior and the resonance appears to shift to lower fields. These non-Lorentzian line shapes are discussed with reference to similar behavior in other spin-glasses.