STRUCTURAL, OPTICAL AND MAGNETIC PROPERTIES OF Cr-DOPED ZnO

Abstract

The III-V and II-VI diluted magnetic semiconductors (DMSs) have attracted considerable attention because the spin-dependent magnetic phenomena can be manipulated in these low-dimensional tailored magnetic thin films for various spin-based devices to unprecedented capabilities. The prediction of room temperature ferromagnetism (RTFM) in transition metal (TM)-doped ZnO has initiated enormous efforts on the preparation of a ZnO based diluted magnetic semiconductor during the last years. Besides the mostly studied ZnO:Co and ZnO:Mn systems, doping of ZnO with Cr might be attractive as according to theoretical predictions Cr-doping may result in a ferromagnetic state which is more stable than a spin glass state. However, the magnetic properties of Cr-doped ZnO are discussed controversially in the literature and also seem to be sensitive to the preparation method. We report on the structural, optical and magnetic properties of bulk samples of ZnCr,,O (x=0.00, 0.02, 0.05. 0.08 and 0.10) synthesized by solid state reaction method. X-ray diffraction (XRD) study of the samples reveal the shifting in peaks due to Cr-doping and some impurity phases appear in the synthesized samples. FE-SEM study reveals that the average grain size of the samples is increase with increase in the sintering temperature. EDAX give the chemical composition of our samples according to our doping concentration. UV—VIS-NIR spectroscopy showed that the reflectance intensity decreases with increase in Cr concentration. PL study suggests the presence of defects in the Cr-doped ZnO samples in addition to the presence of NBE band. The magnetic measurements show ferromagnetism for x=0.10 at room temperature for sample sintered at 800 °C & annealed in Ar/H2. From the M-T measurements it is found that antiferromagnetic component in the sample decreases (ferromagnetic component increases) with increase in the Cr concentration, the and anti-ferromagnetic component decreases. Similar results have been observed from their M-H curves. The observed room temperature ferromagnetism (RTFM) in the present case may be attributed to the oxygen vacancies produced on annealing the sample in reducing atmosphere (Ar/H2).