Tuning interfacial exchange interactions via electronic reconstruction in transition-metal oxide heterostructures

Li, Binzhi; Chopdekar, Rajesh V.; N’Diaye, Alpha T.; Mehta, Apurva; Byers, James P.; Browning, Nigel D.; Arenholz, Elke; Takamura, Yayoi

doi:10.1063/1.4964407

Cited by 23 publications

(34 citation statements)

References 31 publications

(40 reference statements)

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“…There is a sampling depth limitation of the EY signal, which makes it a surface sensitive mode [42]. In contrast, the LY detection mode is bulk sensitive, capturing information over the entire film thickness [43,44]. As shown in Figure 5, the F K-edge EY and LY spectra are observed only in the PVF and PVDF fluorinated SMOF films, consistent with the higher F concentration in PVF and PVDF fluorinated films probed by XPS in Figure 2.…”

Section: Methodssupporting

confidence: 61%

Effect of fluoropolymer composition on topochemical synthesis of SrMnO3−δFγ oxyfluoride films

Wang

Shin

Arenholz

et al. 2018

Phys. Rev. Materials

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We report the synthesis of SrMnO 3- F  perovskite oxyfluoride thin films using a vapor transport method to fluorinate as-grown SrMnO 2.5 epitaxial thin films. The influence of the fluoropolymer, which acts as a fluorine vapor source, was investigated by utilizing polyvinyl fluoride (PVF), polyvinylidene difluoride (PVDF) and polytetrafluoroethylene (PTFE) in the reaction. The same process was carried out with polyethylene (PE) to isolate the role of carbon in the vapor transport process. The F distribution was probed by X-ray photoemission spectroscopy, which confirmed the incorporation of F into the films and revealed higher F concentrations in films exposed to PVF and PVDF compared to PTFE. The c-axis parameter expands after fluorination, a result consistent with density functional theory calculations that attribute the volume expansion to elongated Mn-F bonds compared to shorter Mn-O bonds. Using X-ray absorption spectroscopy, we show that the fluorination process reduces the nominal Mn oxidation state suggesting that F accommodate [11]. Early synthesis efforts of transition metal oxyfluorides were carried out by solid-state reactions at around 1000°C [12]. In order to reduce the synthesis temperature, topochemical fluorination of metal oxide precursors with fluorine sources including F 2 , NH 4 F, MF 2 (M = Ba, Cu, Ni, Zn), and XeF 2 was utilized, significantly reducing the reaction temperature [5]. This fluorination method has been reported in producing powder samples of copper, titanium, iron, manganese and other metal oxyfluorides [3][4][5][6]13].An alternative approach to fluorination at low temperatures was introduced by Slater [14], who demonstrated that polyvinylidene difluoride (PVDF) can be used as a fluorine vapor source when decomposed in close proximity to metal oxide powders. Following the work of Slater, PVDF has been applied in fluorination of other metal oxide samples in powder form, especially in producing the perovskite-related oxyfluoride materials [9,[15][16][17]. The use of fluoropolymers can further reduce the fluorination temperature to 180°C for PVDF and 330°C for polytetrafluoroethylene (PTFE) [11], and mitigate the formation of secondary phases.Additionally, polymer-based fluorination has been applied to the synthesis of oxyfluoride thin films, carried out as post-growth reaction on as-grown films [18][19][20][21]. To date, these fluorination studies of thin films have all utilized PVDF as the fluorine source, while PTFE has been only investigated in producing bulk oxyfluorides [22]. To the best of our knowledge, polyvinyl fluoride (PVF) has not been reported as a fluorinating agent yet. Thus, there has been no systematic report of how the choice of fluoropolymer influences the fluorination reaction and resultant oxyfluoride films.We have synthesized epitaxial SrMnO 3- F  (SMOF) oxyfluoride thin films by fluorinating the as-grown SrMnO 2.5 (SMO) films with PVF, PVDF, and PTFE. We find that the use of PVDF and PVF results in more F incorporation than PTFE; however, the crystalline...

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Section: Methodssupporting

confidence: 61%

Effect of fluoropolymer composition on topochemical synthesis of SrMnO3−δFγ oxyfluoride films

Wang

Shin

Arenholz

et al. 2018

Phys. Rev. Materials

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“…The vertical extent of this magnetic coupling suggests that the charge transfer extends up to 5-6 u.c. from the interface in either direction, which is in reasonable agreement with numbers quoted in other perovskite systems [36,39,45,46]. This unique behavior of the LSMO/LSCO SLs results due to the differences in electronic characteristics of the Co and Mn ions, and differs to other systems such as the manganite/ ruthenate system involving much heavier Ru ions where decoupled properties have been observed down to ultra-thin sublayers [47,48].…”

Section: Maximum Of Dρ(t) Dtsupporting

confidence: 89%

Nanostructured complex oxides as a route towards thermal behavior in artificial spin ice systems

Chopdekar

Wynn

et al. 2017

Phys. Rev. Materials

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We have used soft x-ray photoemission electron microscopy to image the magnetization of single domain La0.7Sr0.3MnO3 nano-islands arranged in geometrically frustrated configurations such as square ice and kagome ice geometries. Upon thermal randomization, ensembles of nanoislands with strong inter-island magnetic coupling relax towards low-energy configurations. Statistical analysis shows that the likelihood of ensembles falling into low-energy configurations depends strongly on the annealing temperature. Annealing to just below the Curie temperature of the ferromagnetic film (TC = 338 K) allows for a much greater probability of achieving low energy configurations as compared to annealing above the Curie temperature. At this thermally active temperature of 325 K, the ensemble of ferromagnetic nano-islands explore their energy landscape over time and eventually transition to lower energy states as compared to the frozen-in configurations obtained upon cooling from above the Curie temperature. Thus, this materials system allows for a facile method to systematically study thermal evolution of artificial spin ice arrays of nano-islands at temperatures modestly above room temperature.

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“…The XA/ XMCD spectra suggest that the coupled magnetic properties arise due to an interfacial charge transfer of the form Mn 3+ + Co 4+ → Mn 4+ + Co 3+ , which then promotes a FM exchange coupling vertically across the LSMO/LSCO interface. This effect differs from that seen in LSCO/LSMO bilayers where the LSCO layer was grown directly on the LSAT substrate and magnetic coupling between Co 2+ and Mn 4+ ions with large magnetic moment was observed in the XA/XMCD spectra [39]. The vertical extent of this magnetic coupling suggests that the charge transfer extends up to 5-6 u.c.…”

Section: Maximum Of Dρ(t) Dtmentioning

confidence: 59%

“…In contrast, the LSCMO film more closely resembles a mixture of Co 2+ /Co 3+ valence states with a larger weight on the pre-peak and shoulder features at the Co-L 3 edge. The dominance of magn etically active Co 2+ ions was also observed in LSCO/LSMO bilayers where the LSCO layer was grown directly on the LSAT substrate, pointing to characteristics of a buried LSCO/LSMO interface [39]. With the TEY measurements, the Mn-XA/XMCD signal emanates primarily from the portion of the LSMO sublayer in proximity to the top LSMO/LSCO interface, and the signal could not be detected above the noise floor for the m > 12 SLs.…”

Section: Maximum Of Dρ(t) Dtmentioning

confidence: 84%

Engineered superlattices with crossover from decoupled to synthetic ferromagnetic behavior

Chopdekar¹,

Malik²,

Kane³

et al. 2017

J. Phys.: Condens. Matter

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TitleEngineered superlattices with crossover from decoupled to synthetic ferromagnetic behavior IntroductionDue to the strong coupling between the charge, spin, orbital, and lattice degrees of freedom, perovskite oxides with the chemical formula ABO 3 display a wide range of technologically relevant properties including ferromagnetism, ferroelectricity, and superconductivity [1]. Modern thin film growth techniques such as pulsed laser deposition (PLD) offer atomic scale control of the chemical composition, structural properties, and thickness of sublayers, and therefore have enabled the engineering of artificial composite materials which display emergent properties which differ from those of the constituent materials [2,3]. In these systems, interfacial interactions such as structural effects (i.e. breaking the 3D symmetry of the material, epitaxial strain, and modifications of the inherent BO 6 octahedral tilts/rotations), chemical effects (i.e. atomic intermixing), electronic effects (i.e. electronic/orbital reconstruction, charge transfer), and magnetic effects (i.e. exchange interactions, finite size effects associated with 2D layers) become important [4,5]. The competition between multiple interactions places a great challenge on our ability to understand and predict the resulting functional properties, and ultimately to exploit the emergent properties in applications.In this work, we explore the extent of interfacial interactions occurring in superlattices (SLs) composed of two ferromagnetic (FM) and metallic perovskite oxides, La 0.7 Sr 0. AbstractThe extent of interfacial charge transfer and the resulting impact on magnetic interactions were investigated as a function of sublayer thickness in La 0.7 Sr 0.3 MnO 3 /La 0.7 Sr 0.3 CoO 3 ferromagnetic superlattices. Element-specific soft x-ray magnetic spectroscopy reveals that the electronic structure is altered within 5-6 unit cells of the chemical interface, and can lead to a synthetic ferromagnet with strong magnetic coupling between the sublayers. The saturation magnetization and coercivity depends sensitively on the sublayer thickness due to the length scale of this interfacial effect. For larger sublayer thicknesses, the La 0.7 Sr 0.3 MnO 3 and La 0.7 Sr 0.3 CoO 3 sublayers are magnetically decoupled, displaying two independent magnetic transitions with little sublayer thickness dependence. These results demonstrate how interfacial phenomena at perovskite oxide interfaces can be used to tailor their functional properties at the atomic scale.

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Tuning interfacial exchange interactions via electronic reconstruction in transition-metal oxide heterostructures

Cited by 23 publications

References 31 publications

Effect of fluoropolymer composition on topochemical synthesis of SrMnO3−δFγ oxyfluoride films

Effect of fluoropolymer composition on topochemical synthesis of SrMnO3−δFγ oxyfluoride films

Nanostructured complex oxides as a route towards thermal behavior in artificial spin ice systems

Engineered superlattices with crossover from decoupled to synthetic ferromagnetic behavior

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