Defect-band mediated ferromagnetism in Gd-doped ZnO thin films

Singaravelu, Venkatesh; Franklin, Joseph B.; Ryan, Mary P.; Lee, J.-S.; Ohldag, Hendrik; McLachlan, Martyn A.; Alford, Neil McN.; Roqan, Iman S.

doi:10.1063/1.4905585

Cited by 47 publications

(22 citation statements)

References 45 publications

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“…The exchange interaction is therefore dependent on the Gd concentration. Subramanian et al [16] observed anisotropy in polycrystalline Gd-doped ZnO [23].…”

Section: The Effect Of Oxygen Deficiencymentioning

confidence: 99%

“…In this case, the band broadening formed by intrinsic defects is resonant with Gd f states producing RTFM [52], as shown in Figure 13. Venkatesh et al [23] showed that the formation of a Gdoxygen-deficiency defect band located near the Fermi level mediated the ferromagnetism through spin splitting of the defect band [22].…”

Section: The Origin Of the Ferromagnetism In Gd-doped Zno Filmsmentioning

confidence: 99%

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Magnetic Properties of Gadolinium-Doped ZnO Films and Nanostructures

Roqan¹,

Aravindh²,

Singaravelu³

2016

Magnetic Materials

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The magnetic properties of Gd-doped ZnO films and nanostructures are important to the development of next-generation spintronic devices. Here, we elucidate the significant role played by Gd-oxygen-deficiency defects in mediating/inducing ferromagnetic coupling in in situ Gd-doped ZnO thin films deposited at low oxygen pressure by pulsed laser deposition (PLD). Samples deposited at higher oxygen pressures exhibited diamagnetic responses. Vacuum annealing was used on these diamagnetic samples (grown at a relatively high oxygen pressures) to create oxygendeficiency defects with the aim of demonstrating reproducibility of room-temperature ferromagnetism (RTFM). Samples annealed at oxygen environment exhibited superparamagnetism and blocking-temperature effects. The samples possessed secondary phases; Gd segregation led to superparamagnetism. Theoretical studies showed a shift of the 4f level of Gd to the conduction band minimum (CBM) in Gd-doped ZnO nanowires, which led to an overlap with the Fermi level, resulting in strong exchange coupling and consequently RTFM.

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“…The exchange interaction is therefore dependent on the Gd concentration. Subramanian et al [16] observed anisotropy in polycrystalline Gd-doped ZnO [23].…”

Section: The Effect Of Oxygen Deficiencymentioning

confidence: 99%

Section: The Origin Of the Ferromagnetism In Gd-doped Zno Filmsmentioning

confidence: 99%

Magnetic Properties of Gadolinium-Doped ZnO Films and Nanostructures

Roqan¹,

Aravindh²,

Singaravelu³

2016

Magnetic Materials

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“…Near edge X-ray absorption fine structure spectra at the O K-edge and Gd M5,4-edges indicated that Gd atoms replace Zn sites. 38,63 Therefore, the incorporation of Gd dopants creates a donor band below the conduction band maximum. Due to the donor band created near the CBM, a shift in the Fermi level occurs, and the material Please do not adjust margins Please do not adjust margins conductivity increases.…”

Section: Growth Mechanismmentioning

confidence: 99%

Homogeneous vertical ZnO nanorod arrays with high conductivity on an in situ Gd nanolayer

et al. 2015

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CitationFlemban TH, Singaravelu V, Sasikala Devi AA, Roqan IS (2015 We demonstrate a novel, one-step, catalyst-free method for the production of size-controlled vertical highly conductive ZnO NR arrays with highly desirable characteristics by pulsed laser deposition using a Gd-doped ZnO target. Our study shows that an in situ transparent and conductive Gd nanolayer (with a uniform thickness of ~1 nm) at the interface between a latticematched (11-20) a-sapphire substrate and ZnO is formed during the deposition. This nanolayer significantly induces relaxation mechanism that controls the dislocation distribution along the growth direction; which consequently improves the formation of homogeneous vertically aligned ZnO NRs. We demonstrate that both the lattice orientation of the substrate and the Gd characteristics are important in enhancing the NR synthesis, and we report precise control of the NR density by changing the oxygen partial pressure. We show that these NRs possess high optical and electrical quality, with a mobility of 177 cm 2 (V.s), which is comparable to the best-reported mobility of ZnO NRs. Therefore, this new and simple method has significant potential for improving the performance of materials used in a wide range of electronic and optoelectronic applications.

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“…In addition, Gddoped/implanted ZnO exhibited room temperature (RT) ferromagnetic behavior that has been attributed to defect/impurity bands mediated by Gd dopants. [7][8][9][10][11][12] Another interesting phenomenon that has been observed in Gd-doped ZnO is a Kondo-like effect, occurring due to a coupling between carriers and localized spin. 13 More specifically, the electrostatic tuning of Kondo effect in Gd-doped ZnO was demonstrated for electrical-double layer transistor applications.…”

Section: Introductionmentioning

confidence: 99%

Identifying the influence of the intrinsic defects in Gd-doped ZnO thin-films

Flemban

Sequeira

Zhang

et al. 2016

Journal of Applied Physics

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Gd-doped ZnO thin films were prepared using pulsed laser deposition at different oxygen pressures and varied Gd concentrations. The effects of oxygen deficiency-related defects on the Gd incorporation, optical and structural properties, were explored by studying the impact of oxygen pressure during deposition and post-growth thermal annealing in vacuum. Rutherford Backscattering Spectrometry revealed that the Gd concentration increases with increasing oxygen pressure for samples grown with the same Gd-doped ZnO target. Unexpectedly, the c-lattice parameter of the samples tends to decrease with increasing Gd concentration, suggesting that Gd-defect complexes play an important role in the structural properties. Using low-temperature photoluminescence (PL), Raman measurements and density functional theory calculations, we identified oxygen vacancies as the dominant intrinsic point defects. PL spectra show a defect band related to oxygen vacancies for samples grown at oxygen deficiency. V C 2016 AIP Publishing LLC.

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Defect-band mediated ferromagnetism in Gd-doped ZnO thin films

Cited by 47 publications

References 45 publications

Magnetic Properties of Gadolinium-Doped ZnO Films and Nanostructures

Magnetic Properties of Gadolinium-Doped ZnO Films and Nanostructures

Homogeneous vertical ZnO nanorod arrays with high conductivity on an in situ Gd nanolayer

Identifying the influence of the intrinsic defects in Gd-doped ZnO thin-films

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