Ferromagnetism in Fe-doped SnO2 thin films

Abstract

Thin films grown by pulsed-laser deposition from targets of Sn 0.95 Fe 0.05 O 2 are transparent ferromagnets with Curie temperature and spontaneous magnetization of 610 K and 2.2 A m 2 kg Ϫ1 , respectively. The 57 Fe Mössbauer spectra show the iron is all high-spin Fe 3ϩ but the films are magnetically inhomogeneous on an atomic scale, with only 23% of the iron ordering magnetically. The net ferromagnetic moment per ordered iron ion, 1.8 B , is greater than for any simple iron oxide with superexchange interactions. Ferromagnetic coupling of ferric ions via an electron trapped in a bridging oxygen vacancy (F center͒ is proposed to explain the high Curie temperature. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1650041͔ First generation spin electronics 1 was based on magnetoresistive sensors and memory elements using electrodes made from alloys of the ferromagnetic 3d metals Fe, Co and Ni. There is an ongoing quest for ferromagnetic semiconductors with a Curie temperature well above room temperature, which could be used for a second generation of spin electronics, as well as a search for transparent ferromagnets which can add an optoelectronic dimension. Much recent interest has been generated by high temperature ferromagnetism in oxide and nitride materials such as ZnO with Co or Mn doping, 2-4 TiO 2 ͑anatase͒ with Co, 5 GaN with Mn, 6 AlN with Cr, 7 and SnO 2 with Mn ͑Ref. 8͒ or Co. 9 Doubts linger as to whether these are homogeneous, single-phase materials, particularly since the well-accepted mechanisms for ferromagnetic coupling, via spin-polarized p-band holes like those in Ga 1Ϫx Mn x As, 10 or via double exchange as in mixed valence manganites, 11 do not seem to apply in these oxides and nitrides.Following a recent report by Ogale et al. 9 of high temperature ferromagnetism with a giant cobalt moment in Codoped SnO 2 , we undertook an investigation of the magnetism of Fe-doped SnO 2 . We find atomic-scale inhomogeneity and remarkably strong ferromagnetism, for which a novel ferromagnetic exchange mechanism is suggested.Ceramic targets of Sn 0.95 Fe 0.05 O 2 were first prepared by solid-state reaction of SnO 2 and FeO or 57 Fe 2 O 3 at 1150°C. Rietveld analysis of the x-ray diffraction patterns of the targets showed SnO 2 with a trace of ␣-Fe 2 O 3 ͑Fig. 1͒. Elemental maps of the targets obtained by energy-dispersive x-ray ͑EDAX͒ diffraction indicated a nonuniform iron distribution, with some tendency to accumulate iron in regions 2-4 m in size which were identified as Sn-doped hematite. The ceramics were ferromagnetic, with magnetization at 5 K of 2.3 A m 2 kg Ϫ1 (Ϸ1.2 B /Fe), and a Curie temperature of 360 K. Mössbauer spectra showed that all the iron was highspin Fe 3ϩ , and 88% of it was magnetically ordered with a hyperfine field of 53.3 T at 19 K. The ferromagnetism cannot be attributed to the Sn-doped hematite, which is a canted antiferromagnet with a weak net moment. 12 The thin films were deposited on R-cut sapphire substrates using a KrF excimer laser operating at 248 nm and 10 Hz. Laser ...

Microstructural Investigation, Raman and Magnetic Studies on Chemically Synthesized Nanocrystalline Ni-Doped Gadolinium Oxide (Gd1.90Ni0.10O3−δ)

“…the Ni cations, the observed magnetic ordering cannot be explained by the carrier mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetic exchange mechanism reported by Hou et al 33 The RKKY interaction is based on the concentration of free carrier, but at such a low doping Gd 2 O 3 cannot transform into a metal. Coey et al, 21 reported the oxygen vacancy mediated ferromagnetism, which is related to the formation of bound magnetic polarons. Among different possibilities, the most plausible explanation for the present case is the defect/oxygen vacancy mediated F centre exchange (FCE) coupling mechanism, as the sample is annealed in vacuum and the formation of oxygen vacancy in the sample can be substantiated by the Rietveld analysis of GNO.…”

“…32 According to FCE mechanism the direct exchange interaction between two Ni ions through oxygen vacancy is ferromagnetic in nature which leads to the alignment of the spin of the magnetic atom. 21,32,36 The concentration of BMPs at relatively high temperature is quite low 17,18 and only few Ni ions are ferromagnetically coupled through oxygen vacancies which contribute weak ferromagnetic ordering in the sample. 32 With the lowering of temperature the decrease in thermal randomization of magnetic spins and the increase of FCE interaction mediated by oxygen vacancy due to increase of BMP concentration favours the dominance of FM phase in GNO and thus strengthens the ferromagnetic exchange interaction at lower temperature.…”

“…The onset of ferromagnetism (FM) in GNO are successfully explained by oxygen vacancy mediated FM or socalled F-centre exchange (FCE) coupling mechanism. 21 In FCE mechanism an electron is trapped in oxygen vacancy which acts as a coupling centre, through which doped magnetic ions align in ferromagnetic order.…”

Structural, optical and magnetic properties of Ni-doped ZnO micro-rods grown by the spray pyrolysis method

“…Early studies explained that a free carrier mediated mechanism was responsible for the ferromagnetic behavior [10]. However, more recent studies proposed that defects like oxygen vacancies give rise to ferromagnetic ordering in oxide based DMS [17].…”

Study The Electrical Properties of Co/TiO2 Multilayer Thin Films

“…In several cases, TM doped oxide such as Co doped ZnO, TiO 2 and SnO 2 etc. shows ferromagnetism at room temperature [5][6][7][8][9][10][11][12]. The mechanism and origin of ferromagnetism and its reproducibility is still studied.…”