Competition between charge- and spin-density waves in transition-metal dichalcogenides

We examine the consequences of competition between charge and spin-density waves in impure transition-metal dichalcogenides within the context of a Landau-Ginzburg mean-field theory. Magnetic impurities enhance a stable spin-density wave and stabilize an unstable one, while tending at the same time to suppress the charge-density wave. The formation of the spin-density wave is used to explain features of the magnetization, Hall-effect, resistivity, and negative magnetoresistance data for iron-doped Ta${\mathrm{Se}}_2$. Randomness in the impurity position leads to randomness in the phase and amplitude of the spin-density wave, giving rise to a novel kind of spin glass, which we call a "spin-density-wave glass" and which, in this particular material, occurs against the background of a smeared charge-density wave.