Antiferromagnetism in bulk Zn[sub 1 - x]Co[sub x]O magnetic semiconductors prepared by the coprecipitation technique
Polycrystalline Zn1−xCoxO diluted magnetic semiconductors have been prepared by coprecipitation technique in the concentration range 0 ⩽ x ⩽ 0.1. Structure, composition analysis, and optical absorption measurements revealed that cobalt is incorporated into the lattice, as Co2+ substituting Zn2+ ions, forming a solid solution with wurtzite structure instead of Co precipitates. Room- and low-temperature magnetization measurements reveal a paramagnetic behavior for the Co-doped ZnO samples with a paramagnetic Co amount smaller than the nominal concentration. χT versus T evidenced that the remaining Co is antiferromagnetically coupled through oxygen. This is further supported by a simple model that shows that as the Co concentration increases the amount of nearest neighbors Co atoms increases thus giving antiferromagnetic coupling and reducing the paramagnetic contribution.