Electrical transport and optical band gap of NiFe2Ox thin films

Bougiatioti, Panagiota; Manos, Orestis; Klewe, Christoph; Meier, Daniel; Teichert, Niclas; Schmalhorst, Jan-Michael; Kuschel, Timo; Reiss, Günter

doi:10.1063/1.4999428

Cited by 29 publications

(22 citation statements)

References 43 publications

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“…When two different metal cations are incorporated into the spinel structure, the possibility of changing the stoichiometry and the cation distribution allows to tune the electronic and magnetic properties over a large range. In particular, nickel ferrite, NiFe 2 O 4 (NFO) has attracted interest due to a high Curie temperature of 850 K, good insulating behaviour with a band gap of ∼1.5 eV 4 and a large exchange splitting. Furthermore, changing the conditions of the preparation method 5 allows to fine tune its properties, even to the point of ordering the Ni cations in octahedral sites 6,7 (the Ni cations have a strong preference towards the octahedral sites, i.e., NFO is an inverse spinel).…”

Section: Introductionmentioning

confidence: 99%

Structure and magnetism of ultrathin nickel-iron oxides grown on Ru(0001) by high-temperature oxygen-assisted molecular beam epitaxy

Mandziak

Figuera

Ruiz-Gómez

et al. 2018

Sci Rep

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We demonstrate the preparation of ultrathin Fe-rich nickel ferrite (NFO) islands on a metal substrate. Their nucleation and growth are followed in situ by low-energy electron microscopy (LEEM). A comprehensive characterization is performed combining LEEM for structural characterization and PEEM (PhotoEmission Electron Microscopy) with synchrotron radiation for chemical and magnetic analysis via X-ray Absorption Spectroscopy and X-ray Magnetic Circular Dichroism (XAS-PEEM and XMCD-PEEM, respectively). The growth by oxygen-assisted molecular beam epitaxy takes place in two stages. First, islands with the rocksalt structure nucleate and grow until they completely cover the substrate surface. Later three-dimensional islands of spinel phase grow on top of the wetting layer. Only the spinel islands show ferromagnetic contrast, with the same domains being observed in the Fe and Ni XMCD images. The estimated magnetic moments of Fe and Ni close to the islands surface indicate a possible role of the bi-phase reconstruction. A significant out-of-plane magnetization component was detected by means of XMCD-PEEM vector maps.

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Section: Introductionmentioning

confidence: 99%

Structure and magnetism of ultrathin nickel-iron oxides grown on Ru(0001) by high-temperature oxygen-assisted molecular beam epitaxy

Mandziak

Figuera

Ruiz-Gómez

et al. 2018

Sci Rep

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“…A short description of the band gab determination can be found in the Supplemental Materials V [30] (including Refs. [13,32,[38][39][40]). It is clearly observed that the more conducting samples are characterized by lower band gap energies, reflecting the existence of additional electronic states in the band gap.…”

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confidence: 99%

Quantitative Disentanglement of the Spin Seebeck, Proximity-Induced, and Ferromagnetic-Induced Anomalous Nernst Effect in Normal-Metal–Ferromagnet Bilayers

et al. 2017

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We identify and investigate thermal spin transport phenomena in sputter-deposited Pt/NiFe2O4-x (4 ≥ x ≥ 0) bilayers. We separate the voltage generated by the spin Seebeck effect from the anomalous Nernst effect contributions and even disentangle the intrinsic anomalous Nernst effect (ANE) in the ferromagnet (FM) from the ANE produced by the Pt that is spin polarized due to its proximity to the FM. Further, we probe the dependence of these effects on the electrical conductivity and the band gap energy of the FM film varying from nearly insulating NiFe2O4 to metallic Ni33Fe67. A proximity-induced ANE could only be identified in the metallic Pt/Ni33Fe67 bilayer in contrast to Pt/NiFe2Ox (x > 0) samples. This is verified by the investigation of static magnetic proximity effects via x-ray resonant magnetic reflectivity.In the emerging fields of spintronics Pt is employed frequently for generating and detecting pure spin currents, if adjacent to an FMI, although the possibility of magnetic proximity effects (MPEs) has to be taken into account. Due to its close vicinity to the Stoner criterion [11] the FM can potentially generate a Pt spin polarization at the interface. Consequently, this might induce additional parasitic effects preventing the correct interpretation of the measured ISHE voltage. Therefore, a comprehensive investigation regarding the magnetic properties of the NM/FM interface is required to distinguish the contributions of such parasitic voltages from the ISHE voltage generated by a pure spin current.In the case of SSE, the driving force for the spin current in the FM or FMI is a temperature gradient. When a spin current is generated parallel to a temperature gradient, it is generally attributed to the longitudinal spin Seebeck effect (LSSE) [4,5]. However, when using the ISHE in an adjacent NM for the spin current detection, not only a proximity-induced ANE [12] can contaminate the LSSE signal, but also an additional intrinsic ANE contribution could be present in case of studying ferromagnetic metals (FMMs) or semiconducting ferro(i)magnets [13,14]. Mainly NM/FMI bilayers have been investigated, while LSSE studies on NM/FMM are quite rare.However, Ramos et al. [14][15][16][17] and Wu et al. [18] individually investigated the LSSE in magnetite, which is conducting at room temperature (RT) and, thus, has an intrinsic ANE contribution. They identified the LSSE in Pt/Fe 3 O 4 [14] and CoFeB/Fe 3 O 4 bilayers [18] by using temperatures below the conductor-insulator transition of magnetite (Verwey transition at 120 K) in order to exclude any intrinsic ANE contribution. Ramos et al. further investigated the ANE in bulk magnetite without any Pt [15] and concluded that the ANE contributions for Pt/Fe 3 O 4 bilayers and multilayers should be quite small [16,17]. In addition, Lee et al. [19] and Uchida et al. [20,21] discussed that in Pt/FMM multilayers both LSSE and ANE contribute, but did not disentangle the effects quantitatively. Hence, a clear quantitative disentanglement of the LSSE in the FMM [22], the ...

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“…Generally, for semiconductors, the band conduction governs the charge transport properties at high temperature 31 . In band conduction, charge carriers from localized states are thermally activated and transported to the delocalized states.…”

Section: Resultsmentioning

confidence: 99%

“…6. The universal equation governing these conduction mechanisms in semiconductors is given by 31 where ρ ο is the resistivity coefficient, E t is the transition energy, k B is the Boltzmann constant and P (>0) is the characteristic exponent. The exponent P defines a different kinds of mechanisms based upon the density of states at Fermi level 31 .…”

Section: Resultsmentioning

confidence: 99%

“…The universal equation governing these conduction mechanisms in semiconductors is given by 31 where ρ ο is the resistivity coefficient, E t is the transition energy, k B is the Boltzmann constant and P (>0) is the characteristic exponent. The exponent P defines a different kinds of mechanisms based upon the density of states at Fermi level 31 . For band conduction P = 1, and for variable range hopping P lies between 0 and 1 32 .

Figure 6Schematics showing the conduction mechanisms as a function of temperature.…”

Section: Resultsmentioning

confidence: 99%

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Tuning the Electrical and Thermoelectric Properties of N Ion Implanted SrTiO3 Thin Films and Their Conduction Mechanisms

Bhogra

Masarrat

Meena

et al. 2019

Sci Rep

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The SrTiO3 thin films were fabricated by pulsed laser deposition. Subsequently ion implantation with 60 keV N ions at two different fluences 1 × 1016 and 5 × 1016 ions/cm2 and followed by annealing was carried out. Thin films were then characterized for electronic structure, morphology and transport properties. X-ray absorption spectroscopy reveals the local distortion of TiO6 octahedra and introduction of oxygen vacancies due to N implantation. The electrical and thermoelectric properties of these films were measured as a function of temperature to understand the conduction and scattering mechanisms. It is observed that the electrical conductivity and Seebeck coefficient (S) of these films are significantly enhanced for higher N ion fluence. The temperature dependent electrical resistivity has been analysed in the temperature range of 80–400 K, using various conduction mechanisms and fitted with band conduction, near neighbour hopping (NNH) and variable range hopping (VRH) models. It is revealed that the band conduction mechanism dominates at high temperature regime and in low temperature regime, there is a crossover between NNH and VRH. The S has been analysed using the relaxation time approximation model and dispersive transport mechanism in the temperature range of 300–400 K. Due to improvement in electrical conductivity and thermopower, the power factor is enhanced to 15 µWm−1 K−2 at 400 K at the higher ion fluence which is in the order of ten times higher as compared to the pristine films. This study suggests that ion beam can be used as an effective technique to selectively alter the electrical transport properties of oxide thermoelectric materials.

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Electrical transport and optical band gap of NiFe2Ox thin films

Cited by 29 publications

References 43 publications

Structure and magnetism of ultrathin nickel-iron oxides grown on Ru(0001) by high-temperature oxygen-assisted molecular beam epitaxy

Structure and magnetism of ultrathin nickel-iron oxides grown on Ru(0001) by high-temperature oxygen-assisted molecular beam epitaxy

Quantitative Disentanglement of the Spin Seebeck, Proximity-Induced, and Ferromagnetic-Induced Anomalous Nernst Effect in Normal-Metal–Ferromagnet Bilayers

Tuning the Electrical and Thermoelectric Properties of N Ion Implanted SrTiO3 Thin Films and Their Conduction Mechanisms

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