Enhanced room-temperature ferromagnetism on (In_0.98−xCo_xSn_0.02)₂O₃ films: magnetic mechanism, optical and transport properties

Abstract

The effects of Co doping on the structural, optical, magnetic and transport properties of (InCoSn)O films grown by RF-magnetron sputtering were systematically investigated by theoretical and experimental techniques. The detailed structural analyses revealed that all the (InCoSn)O films possess the cubic bixbyite structure, with the substitutional Co at the In sites of the InO matrix, while some of the Co atoms form Co metal clusters. Obvious room-temperature (RT) ferromagnetic behavior was observed and the saturated magnetization (M) first increased, then decreased with increased Co concentration, while carrier concentration n decreased monotonically, implying that the Co metal clusters are superparamagnetic and the observed RT ferromagnetism is not mediated by the charge carriers. The Mott variable range hopping (VRH) and hard band gap hopping transport behavior dominates the conduction mechanism of the films, confirming that the carriers are strongly localized. The UV-Vis and photoluminescence (PL) measurements indicate the decreased optical band gap E with Co doping, and further prove that the oxygen vacancies and Co impurity band form defect complexes of donor-acceptor pairs. The density functional theoretical calculations show that the codoped Sn can change the magnetic coupling between two Co ions from antiferromagnetic to ferromagnetic by the new hybridization between the Co 3d states with the Sn induced donor band. It can be concluded that the bound magnetic polaron (BMP) based oxygen vacancies as well as the Co-O-Co ferromagnetic superexchange interaction induced by Sn codoping may be responsible for the intrinsic ferromagnetic ordering in the (InCoSn)O films. These results may provide new insight for understanding the magnetic mechanism of InO based DMS systems.

Nonvolatile Control of the Electronic Properties of In2–xCrxO3 Semiconductor Films by Ferroelectric Polarization Charge

“…Combined with what we explained above, the negative MR is attributed to the formation of BMP caused by the overlap between the orbitals of electrons locally trapped by oxygen vacancy with the d shells of neighboring Cr dopants. − As a result, the BMPs increase with increasing Cr content, leading to the increase in the magnitude of negative MR. Similar phenomena were also observed and calculated in previous research studies [e.g., (In 0.98– x Co x Sn 0.02 ) 2 O 3 , ZnO:Cu, La 2– x Sr x CoMnO 6 , and Zn x Fe 3– x O 4 ]. ,,,, However, excessive doping may lead to antiferromagnetic coupling between nearest neighbor’s BMPs, thus suppresses negative MR. ,, Therefore, the magnitude of negative MR is slightly smaller as the Cr content increases from 8 to 11%. Upon the polarization switching from P r + to P r – , the MR changes from negative to positive and the influences of the FE field effect on the MR is greatly enhanced with increasing Cr content.…”

“…For the ICO008 film and the P r – state of PMN-0.29PT, k f l ≪ 1­(Figure S8, Supporting Information), so the system is in the strongly localized regime. Such a behavior, classically observed in oxide semiconductors, could be explained by the localization phenomenon leading to variable range hopping (VRH) mechanism. − Within the framework of VRH model, the temperature dependence of resistivity can be written as …”

“…The In 2 O 3 semiconductor film not only possesses a wide band gap and a relatively low carrier density (10 18 to 10 19 /cm 3 ) but also a high carrier mobility and excellent transparency (>90%) in the visible region . Moreover, doped In 2 O 3 has been proved to be the diluted magnetic semiconductor (DMS), which exhibits not only room-temperature ferromagnetic behavior but also spin-polarized electrical transport [e.g., magnetoresistance (MR)]. − Besides, the electrical properties of In 2 O 3 films have been proven to be sensitive to carrier density . All of these features make it an ideal material to be integrated with PMN- x PT to form FeFETs with superior performance.…”

Room‐Temperature Reversible and Nonvolatile Tunability of Electrical Properties of Cr‐Doped In2O3 Semiconductor Thin Films Gated by Ferroelectric Single Crystal and Ionic Liquid

“…Wide bandgap oxide semiconductor films (e.g., In 2 O 3 ) are potential candidates to be used as channel materials in FeFETs. The In 2 O 3 possesses not only high conductivity and carrier mobility, and excellent transparency (>90%) in the visible region, but also relatively low carrier density (10 18 –10 19 cm −3 ), making it an idea candidate to be integrated with PMN‐ x PT.…”