Role of Co Clusters and Oxygen Vacancies in the Magnetic and Transport Properties of Co-Doped In₂O₃ Films

Abstract

The (In1–x Co x )2O3 films with x = (0.055, 0.08, 0.10, 0.15) have been prepared by a radio frequency magnetron sputtering technique and investigated by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption fine structure, Hall effect, and room-temperature magnetic measurements. The detailed structural analyses and full multiple-scattering ab initio calculations indicate that most Co2+ ions substitute for In3+ sites of In2O3 lattice and form CoIn2+ + VO complexes with the O vacancy in the nearest coordination shell, whereas a portion of the Co atoms form the precipitate of Co metal clusters for all the (In1–x Co x )2O3 films. Despite the formation of Co clusters, magnetic characterizations show that the saturated magnetization M s of films first increases and then decreases with the increase of Co concentration, suggesting that the small Co clusters are superparamagnetic. The electronic conducting mechanism is dominated by Mott variable range hopping behavior for all the films. The strong localization of carriers suggests the bound magnetic polarons scenario. It can be concluded that the observed room-temperature ferromagnetism in the (In1–x Co x )2O3 films is intrinsic and originates from electrons bound in defect states associated with oxygen vacancies. There exists an optimal localization radius ξ of variable range hopping for achieving the largest M s in the (In1–x Co x )2O3 films.

Effect of Nanoparticle Interaction on Structural, Conducting and Sensing Properties of Mixed Metal Oxides

“…When lattice ions are replaced by doping ions, in contrast to their incorporation into the intercrystallite space, the emerging vacancies can form complexes with these ions. Such complexes were characterized for In 2 O 3 nanocrystals doped with Mn +2 and Co +2 ions [48]. The vacancies formed when these ions are included in the In 2 O 3 lattice, and enter the first coordination sphere of oxygen anions surrounding the doping ion [49].…”

Room-temperature ferromagnetism observed in Nd-doped In 2 O 3 dilute magnetic semiconducting nanowires

“…[13] As an important semiconductor material, In 2 O 3 has been widely studied in various fields including semiconductor spintronics. Since Philip et al reported the interesting carrier-controlled above room-temperature ferromagnetism (RTFM) in transparent Cr-doped In 2 O 3 thin films, [14] there have been abundant research reports on RTFM in In 2 O 3 -based DMSs [15][16][17][18][19][20] as well as in pure In 2 O 3 . [21] However, most of the research focused on the 3d transition metal (TM) doping, [15][16][17][18][19][20] where TM ions occupy the corresponding lattice sites in the host with a dilute concentration to minimize the possibility of anti-ferromagnetic ordering.…”

“…Since Philip et al reported the interesting carrier-controlled above room-temperature ferromagnetism (RTFM) in transparent Cr-doped In 2 O 3 thin films, [14] there have been abundant research reports on RTFM in In 2 O 3 -based DMSs [15][16][17][18][19][20] as well as in pure In 2 O 3 . [21] However, most of the research focused on the 3d transition metal (TM) doping, [15][16][17][18][19][20] where TM ions occupy the corresponding lattice sites in the host with a dilute concentration to minimize the possibility of anti-ferromagnetic ordering. [22] Compared with TMs with open d shells, 4f rare earth (RE) ions may offer the stronger magnetic interaction and anisotropy and thus may possess the larger magnetic moments in doped semiconductors.…”

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.…”