Ferromagnetism inSnO2-based multilayers: Clustering of defects induced by doping

Abstract

Several series of A / SnO 2 and Mn/B multilayers, where A and B are thin layers ͑0.4-10.1 nm͒ of SnO 2 , SiO 2 , Si, Al, Mn, or MnO x , have been investigated magnetic, electronic, and structurally. The study demonstrates that the detected ferromagnetism is related to regions of high density of defects in SnO 2 induced by doping under particular conditions. The observed room-temperature ferromagnetic ͑RTFM͒ signal does not scale to Mn content but increases with the number of interfaces and their roughness. The presence of Mn in 3+ oxidation state in the SnO 2 lattice is a necessary condition but is not enough to promote ferromagnetism which also requires the presence of Sn 2+ . The high oxygen deficiency induced by Mn doping in the tin-oxide layers is mostly compensated by the formation of the stable SnO phase. Moreover, the RTFM signal decreases upon annealing either in O 2 rich or in vacuum atmospheres. The combination of Mn with SiO 2 , Si, or Al produces paramagnetic signals but no ferromagnetism; consequently SnO 2 is a crucial ingredient of this RTFM. The observed ferromagnetism may be explained by short-range ferromagnetic correlations between Mn probably mediated by induced holes at oxygen sites of SnO 2 in the vicinity of trivalent Mn 3+ doping ions. The inhomogeneous Mn distribution inside tin oxide at the multilayer interfaces may produce large enough regions with high defect concentration to allow long-range ferromagnetic order. All undoped SnO 2 films, grown in a wide set of different conditions, show paramagnetic signals with high-J values but no ferromagnetism is detected probably because of the high density of defects required to establish a ferromagnetic order based in a shortrange mechanism.

Tin Oxides: Insights into Chemical States from a Nanoparticle Study

“…In recent years tin oxides, pure and doped, have been advancing over a broad front in nanoscience and nanotechnology: in optoelectronics, − photovoltaics, − magnetism, − gas sensing, − and catalysis. − Out of several possible tin oxides, the one most used is tin­(IV) oxide, SnO 2 , which is a wide-gap semiconductor with natural n-type conductivity. This conductivity has been, as a rule, assigned to the “effective” oxidation state caused by substantial oxygen deficiency in the crystal lattice. ,− At the same time the other stable oxide form, tin­(II) oxide, SnO, has p-type conductivity, , and metal-atom deficiency has been observed in it . Some intermediate/nonstoichiometric tin oxides, SnO x (1 < x < 2), are also known and have been reported to have either p- or n-type conductivity. , All these tin oxides may coexist in laboratory-prepared samples, and the sample composition is strongly dependent on the preparation method.…”

Structural, Electronic, Magnetic, and Hyperfine Properties of V-doped SnO2 (Sn1–xVxO2, x: 0, 0.042, 0.084, and 0.125). A DFT-Based Study

“…Among the universe of materials, oxides exhibit unique structural, electronic, and magnetic properties and possess an exceptional potential as base materials in a broad range of industrial and technological applications including optical, electronic, optoelectronic, and biological fields. − Particularly, rutile-type tin dioxide (SnO 2 ) is maybe one of the most studied metallic oxide , and have attracted a renewed interest. − SnO 2 is a direct n -type semiconductor (a band gap of 3.6 eV, refs and ) that presents high electrical conductivity and transmittance in the ultraviolet–visible region and infrared reflectance. , Its n-type electrical conductivity is originated by intrinsic defects (oxygen vacancies and tin interstitials). The occurrence of transparency and conductivity makes it a suitable candidate for application as an optically passive component in optoelectronic devices such as solar cells, , touch screens, transparent electrodes, solid-state chemical and gas sensors, , catalytic support, secondary lithium battery electrodes, and potential candidates for spintronic devices. − ,− …”

Positron Annihilation Lifetime Studies of Nb‐Doped TiO2, SnO2, and ZrO2

“…For example, Nb‐doping of anatase TiO 2 leads to magnetic moments induced by cation vacancies . Similarly, it has been shown that ferromagnetism in SnO 2 ‐based multilayers is related to defect clustering induced by doping …”