Magnetic properties of ZnO-based diluted magnetic semiconductors

We report a study of the magnetic properties of transition-metal doped ${\mathrm{Zn}}_{\text{1−x}}{\mathrm{TM}}_x\mathrm{O}$ (TM=Mn, Co, Fe). Polycrystalline powder samples were synthesized by both solid-state and liquid-phase reactions. From the Curie–Weiss behavior of susceptibility at high temperatures, it was found that the TM–TM interaction is dominated by antiferromagnetic coupling with effective nearest-neighbor exchange constants $\text{J=−90}$ to −30 K. The magnetization data measured at low temperature as a function field H are fit to a parameterized Brillouin function to obtain the effective concentration $x_{\mathrm{eff}}$ of magnetically active ${\mathrm{TM}}^{\text{2+}}$ ions. As x increases, the fraction of magnetically active ions, $x_{\mathrm{eff}}\mathrm{/x,}$ decreases. This is ascribed to an increase in average AF interaction between doped magnetic spins as the average distance between them decreases with an increase in x.