Effect of the thickness reduction on the structural, surface and magnetic properties of α-Fe2O3 thin films

Aragón, F.F.H.; Ardisson, José D.; Aquino, J. C. R.; González, Ismael; Macedo, W. A. A.; Coaquira, J. A. H.; Mantilla, J.; Silva, S. W. da; Morais, P.C.

doi:10.1016/j.tsf.2016.03.052

Cited by 35 publications

(9 citation statements)

References 22 publications

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“…In the undoped and Sn-doped samples, an inversion of the signs of the dichroism of the first peaks occurs at T =200 K and T =300 K respectively. The transition temperature for the undoped film surface is well below that of the bulk T M =265 K, but it is known that T M varies with thickness in a non-trivial way, depending on strain and/or atomic site vacancies in the lattice 32,33,37 , and our value interpolates well with the recent study of Shimomura et al for similar thicknesses 27 . Inspection of Fig.…”

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confidence: 89%

Magnetic states at the surface of α−Fe2O3 thin films doped with Ti, Zn, or Sn

et al. 2017

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The spin states at the surface of epitaxial thin films of hematite, both undoped and doped with 1% Ti, Sn or Zn, respectively, were probed with x-ray magnetic linear dichroism (XMLD) spectroscopy. Morin transitions were observed for the undoped (TM ≈ 200 K) and Sn-doped (TM ≈300 K) cases, while Zn and Ti-doped samples were always in the high and low temperature phases, respectively.In contrast to what has been reported for bulk hematite doped with the tetravalent ions Sn 4+ and Ti 4+ , for which TM dramatically decreases, these dopants substantially increase TM in thin films, far exceeding the bulk values. The normalized Fe LII -edge dichroism for T < TM does not strongly depend on doping or temperature, except for an apparent increase of the peak amplitudes for T < 100 K. We observed magnetic field-induced inversions of the dichroism peaks. By applying a magnetic field of 6.5 T on the Ti-doped sample, a transition into the T > TM state was achieved. The temperature dependence of the critical field for the Sn-doped sample was characterized in detail. It was demonstrated the sample-to-sample variations of the Fe LIII -edge spectra were, for the most part, determined solely by the spin orientation state. Calculations of the polarization-depedent spectra based on a spin-multiplet model were in reasonable agreement with the experiment and showed a mixed excitation character of the peak structures. PACS numbers: 75.25.-j,75.70.-i,78.70.DmHematite (α-Fe 2 O 3 ) is considered to be a promising material for photoelectrochemical (PEC) cells for solar water splitting 1-3 , whereby solar energy can drive hydrogen-production reactions in water 4 . Introducing impurities, or doping, as a source of free charge carriers is a crucial ingredient to making feasible devices 5,6 . The models and tools of semiconductor device physics are being increasingly used in the ongoing effort to develop such cells using hematite photo-anodes 7 . Yet, the electron-electron interactions arising from its Fe 3+ 3dorbitals, mediated by oxygen atoms, make hematite a strongly correlated system, as evidenced by its antiferromagnetism (AF). In addition to the effect of doping on transport properties in the usual way, the doping can also be used to manipulate the magnetic structure. As to which extent this is also important for the device performance has yet to be explored.A magnetic transition, known as the Morin transition, takes place upon raising the temperature past T M (=265 K for bulk, undoped hematite), which changes the spin-ordering from pure AF to a superposition of AF with weak ferromagnetism 8 . Polarized neutron diffraction 9 , magnetic resonance 10,11 and magnetostriction measurements 12 have since confirmed this and revealed that below T M the spins are aligned antiferromagnetically along the c-axis, with stacked c-planes having alternating up and down spins. The spin arrangements are illustrated in fig. 1. Above T M , the spins are rotated ∼90 • to lie in the c-plane, with AF order still maintained along the c direction, but now with re...

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confidence: 89%

Magnetic states at the surface of α−Fe2O3 thin films doped with Ti, Zn, or Sn

et al. 2017

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“…eV was assigned to the chemisorbed oxygen related species such as hydroxyl groups and to the located oxygen vacancies at the particles surface. The third peak range from 531.6 to 532.1 eV was also attributed to the adsorbed water [20,[40][41][42]. It has been reported that hydroxyl groups (i.e.…”

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confidence: 99%

Systematic study of electronic properties of Fe-doped TiO2 nanoparticles by X-ray photoemission spectroscopy

Nasralla

Yeganeh

Astuti

et al. 2018

J Mater Sci: Mater Electron

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The importance of investigating the electronic structure of Fe doped TiO2 nanoparticles lies in understanding their various magnetic and optical applications. In this study Fe doped TiO2 nanoparticles were synthesized by sol gel method in a wide range of Fe/Ti molar ratios (1, 3, 5, 8, and 10 %) and post annealing at 400, 600 and 800 o C in air. The structure and size of nanoparticles were studied by X-ray diffraction and transmission electron microscopy, respectively. Systematic study of the existing states of Fe ions in Fe doped TiO2 and transformation of the existing states as a function of annealing temperature and Fe concentration were carried out utilizing high-resolution X-ray photoemission spectroscopy (XPS). The XPS results showed that Fe was present in all samples while Fe ions were detected in mixed valence (Fe 2+ and Fe 3+ ) states. The Fe 3+ ions were dominant in the surface region of the nanoparticles. Moreover, the Ti in Fe:TiO2 nanoparticles was assigned to the Ti 4+ while a small shift towards lower binding energies was observed upon increasing the annealing temperature and dopant level. This confirms the successful incorporation of Fe into TiO2, and the shifts in binding energies were attributed to the anatase to rutile transformation. The results verify that doping by Fe up to 10% do not exceed the limit of Fe substitutation into TiO2 lattice.

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“…3(d)], the Morin transition of the 100-nm films used here can be measured in order to confirm the value of T M from electrical measurements. If the films are thinner than this, the Morin transition is heavily suppressed or cannot be resolved [40]. We observe that, when cooled in an external field, the Morin transition of our films is visible from the drop in magnetic moment to effectively zero above the background substrate contributions [Fig.…”

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confidence: 97%

Structural sensitivity of the spin Hall magnetoresistance in antiferromagnetic thin films

et al. 2020

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Reading the magnetic state of antiferromagnetic (AFM) thin films is key for AFM spintronic devices. We investigate the underlying physics behind the spin Hall magnetoresistance (SMR) of bilayers of platinum and insulating AFM hematite (α-Fe 2 O 3 ) and find an SMR efficiency of up to 0.1%, comparable to ferromagnetic-based structures. To understand the observed complex SMR field dependence, we analyze the effect of misalignments of the magnetic axis that arise during growth of thin films, by electrical measurements and direct magnetic imaging, and find that a small deviation can result in significant signatures in the SMR response. This highlights the care that must be taken when interpreting SMR measurements on AFM spin textures.

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Effect of the thickness reduction on the structural, surface and magnetic properties of α-Fe2O3 thin films

Cited by 35 publications

References 22 publications

Magnetic states at the surface of α−Fe2O3 thin films doped with Ti, Zn, or Sn

Magnetic states at the surface of α−Fe2O3 thin films doped with Ti, Zn, or Sn

Systematic study of electronic properties of Fe-doped TiO2 nanoparticles by X-ray photoemission spectroscopy

Structural sensitivity of the spin Hall magnetoresistance in antiferromagnetic thin films

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