Study of the magnetic and structural properties of Mn-, Fe-, and Co-doped ZnO powder

A study of the magnetic and structural properties of Zn-1_xMxO powder (where x=0 or 0.01, and M=Mn, Fe or Co) produced by the proteic sol-gel process was undertaken. The sample crystal structure was analyzed by XRD and magnetic measurements were carried out in a SQUID magnetometer. Of the XRD analysis, all samples had hexagonal wurtzite crystal structure with P63mc space group, and no secondary phase was observed. It is observed of the M(H) measures at 2 K, that the Co- and Mn-doped ZnO displayed saturation magnetizations (M-s) of approximately 2 and 3.2 emu/g, respectively, and no remanence (M-r) was observed, indicating a superparamagnetic behavior in these samples. However, the Fe-doped sample showed a ferromagnetic behavior with M-s similar to 0.34 emu/g, M-r similar to 0.05 emu/g, and coercivity (H-c)similar to 1090 Oe. Already at room temperature, the M(H) measurements reveal a purely paramagnetic behavior for Mn- and Fe-doped ZnO, indicating that the Curie temperature (T-c) is below 300 K. However, a weak superparamagnetic behavior was observed in the Co-doped sample, indicating that T-c > 300 K. (C) 2011 Elsevier B.V. All rights reserved.