A bulk diluted magnetic semiconductor (Sr,K)(Zn,Mn)_2As_2 was synthesized with decoupled charge and spin doping. It has a hexagonal CaAl_2Si_2-type structure with the (Zn,Mn)_2As_2 layer forming a honeycomb-like network. Magnetization measurements show that the sample undergoes a ferromagnetic transition with a Curie temperature of 12 K and magnetic moment reaches about 1.5 μ_B/Mn under μ_0H = 5 T and T = 2 K. Surprisingly, a colossal negative magnetoresistance, defined as [ρ(H)-ρ(0)]/ρ(0), up

more »

... o -38% under a low field of μ_0H = 0.1 T and to -99.8% under μ_0H = 5 T, was observed at T = 2 K. The colossal magnetoresistance can be explained based on the Anderson localization theory.