Structural, optical and magnetic properties of Mn doped ZnO thin films prepared by pulsed laser deposition

摘要

Zn_(1-x)MnxO thin films were grown by pulsed laser deposition. The phase purity and the structure were confirmed by X-ray diffraction studies. The films have a transmittance more than 80% in the visible region. The refractive index of Zn_(0.90)Mn_(0.10)O films is found to be 1.77 at 550 nm. The presence of non-polar E_2~(high) and E_2~(low) Raman modes in thin films indicates that 'Mn' doping does not change the wurtzite structure of ZnO. Apart from the normal modes of ZnO the Zn_(1-x)MnxO ceramic targets show two additional modes at 332 cm~(-1) (I_1) and 524cm~(-1) (I_2). The broad Raman peaks (340-600cm~(-1)) observed Zn_(0.90)Mn_(0.10)O thin films can be deconvoluted into five peaks, denoted as P1-P5. The possible origins of Raman peaks in Zn_(1-x)MnxO films are the structural disorder and morphological change caused by the Mn dopant. The B_1~(low), ~2b_1~(low), B_1~(high) and A_1~(LO) modes as well as the surface phonon mode have been observed in heavily Mn-doped ZnO films. Zn_(0.98)Mn_(0.02)O thin film shows room temperature ferromagnetism. The saturation magnetic moment of the Zno.9sMno.02O thin film is 0.42μB/Mn atom. The undoped ZnO film prepared under the same condition shows diamagnetic nature. At higher doping concentrations the formation of Mn clusters suppress the room temperature ferromagnetism in Zn_(1-x)MnxO thin films and shows paramagnetism. XPS confirms the incorporation of Mn~(2+) into the ZnO lattice.