Optical and Magnetic Properties of Zn_1–xMn_xO Nanorods Grown by Chemical Vapor Deposition

Abstract

We prepared successfully Zn 1−x Mn x O nanorods (x = 0, 0.008, 0.013, and 0.020) by using chemical vapor deposition. Their crystal structural and optical and magnetic properties at room temperature were then investigated in detail. Experimental results have revealed that all the samples have a single phase with the wurtzite structure, and the lattice parameters slightly increase with increasing Mn-doping content. This is ascribed to an incorporation of Mn 2+ into the Zn site of the ZnO host lattice. The Mn incorporation also creates more lattice defects and disorders, which influence directly characteristic photoluminescence (PL) and Raman scattering (RS) spectra of Zn 1−x Mn x O nanorods. For example, there are the blue shift of ultraviolet emission and the rapid decline of visible PL emission when Mndoping content (x) in Zn 1−x Mn x O increases. Besides conventional phononvibration modes, there are additional ones associated with defects and Mn impurities. The origin and nature of these additional modes is identified and assessed carefully. Interestingly, under the resonant-RS condition we have recorded the overtones/replicas of the longitudinal− optical phonon up to the seventh order. Magnetic measurements have been also performed, which reveal Zn 1−x Mn x O nanorods with x = 0.013 and 0.020 exhibiting the room-temperature ferromagnetic order. We believe that the ferromagnetic nature is related to both Mn 2+ ions and intrinsic defects of zinc vacancies, rather than Mn-related secondary phases.

Effect of (Li, Mn) co-doping on structural, optical and magnetic properties of chunk-shaped nano ZnO

“…Although there is a possibility of presence of Zn interstials and oxygen vacancies at surface of undoped ZnO nanocrystals, these defects are not large enough to induce ferromagnetism in undoped ZnO nanocrystals [39]. Recent reports have also shown FM order in pure ZnO nanostructures and assigned it to be generated from intrinsic defects of zinc vacancies [15,75,76]. The absence of defect-induced FM order in pure ZnO nanorods once again proves their high crystal quality.…”

“…Basically, when a TM ion substitutes for the cation of a semiconductor host lattice, the resultant electronic structure is strongly influenced by the hybridization between the 3d orbitals of the magnetic ion and the p orbitals of neighboring anions. This hybridization can lead to magnetic interaction between the localized 3d electrons and the carriers in the valence band of the host lattice [15]. In DMS materials, magnetic transition ions substitute a small percentage of cation sites of the host semiconductor and are coupled with free carriers to yield FM via indirect interaction [16][17][18].…”

“…To our knowledge, there is no report on the chunk-shaped (Li, Mn) co-doped ZnO nanostructures showing a robust FM behavior at RT. Many research works so for, to investigate the optical, thermal, magnetic, and magneto-transport properties of single element doped ZnO, most of them focused on Mn-doped ZnO bulks, films, nanoparticles, and nanowires/nanorods [14,15,18,19,26,44] and only a very few works were focused on (Mn, Li) co-doped ZnO films [28,35,37] and nanoparticles [36].…”

“…This means that some Li atoms replaced Zn atom in zinc site. These V o and V Zn play an important role in establishing a weak FM order in both doped and undoped ZnO materials[15,[67][68][69]. With a higher surface area, the photogenerated holes in the valence band are possibly trapped into the surface defects and are increasingly returned to oxygen vacancies.…”

Structure, optical and magnetic properties of (In1−Fe )2O3 films by magnetron sputtering

“…Following the theoretical prediction by Dietl et al of RT ferromagnetism in ZnO-based DMSs [4], various TM elements (Fe, Co, Ni, Mn, Cr) doped wide-band-gap oxide semiconductors appear to be rather promising candidates. Experimental works on TM-doped-ZnO [5][6][7], TiO 2 [8][9][10], SnO 2 [11,12] as well as In 2 O 3 [13][14][15] in bulk, thin film and nano-particle forms have suggested that TMs certainly could be used to dope in host oxide semiconductors to achieve RT ferromagnetism for practical application. Being one of these candidate hosts, In 2 O 3 is an important n-type directband-gap semiconductor ($3.75 eV) with excellent electrical conductivity and high optical transparency.…”