Abstract
This study reports the structure and the magnetic properties of Zn1-x Ni (x) S nanocrystalline films with Ni composition ratios of 0.05 a parts per thousand currency sign x a parts per thousand currency sign 0.2. Thin films of Zn1-x Ni (x) S were deposited on Corning glass substrates by using an electron-beam evaporation method. X-ray diffraction patterns revealed single- phase films with a cubic zinc-blend-type structure with preferred crystallographic orientations along the (111) and the (220) planes. Evidence for the nanocrystalline nature of the films was observed from the investigations of the surface morphology by using scanning electron microscopy and atomic force microscopy. Magnetic domains were observed by using magnetic force microscopy at room temperature, indicating the existence of ferromagnetism over the film's surface. The magnetic measurements at 5 K revealed a superparamagnetic behavior. However, room-temperature ferromagnetism was observed in all the nanocrystalline Zn1-x Ni (x) S films. The saturation magnetization for the Zn1-x Ni (x) S films was found to increase with increasing dopant concentration (x). An exchange interaction between local spin-polarized electrons (Ni2+ ions) and conductive electrons according to the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction mechanism is proposed as a possible mechanism for the ferromagnetism. These results show that the Ni-doped ZnS nanocrystalline films are promising materials for applications in spintronic and magnetic sensor devices.