Structure determination of monolayer-by-monolayer grown<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi>La</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Sr</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mi>MnO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>thin films and the onset of magnetoresistance

Herger, R.; Willmott, P. R.; Schlepütz, Christian M.; Björck, Matts; Pauli, S. A.; Martoccia, D.; Pàtterson, B. D.; Kumah, Divine P.; Clarke, Roy; Yacoby, Y.; Döbeli, M.

doi:10.1103/physrevb.77.085401

Cited by 80 publications

(66 citation statements)

References 37 publications

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“…These values were in agreement with sharp RHEED specular spot whose intensity was comparable between the starting STO substrate and the LCMO at the end of growth. In order to obtain a reliable value for XAS sampling depth d, nonuniform film thickness or interdiffusion with the substrate should be carefully checked and excluded, as they would tend to increase the measured value for d. We can estimate an upper limit for the interdiffusion between the STO substrate and the LCMO overlayer to about one unit cell [26]. Summing this to an error in thickness of ±0.5 uc gives the error bars used during fits of the sampling depth discussed in Sec.…”

Section: Thin Film Characterizationmentioning

confidence: 99%

Electron sampling depth and saturation effects in perovskite films investigated by soft x-ray absorption spectroscopy

et al. 2014

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Knowledge of the electron sampling depth and related saturation effects is important for quantitative analysis of X-ray absorption spectroscopy data, yet for oxides with the perovskite structure no quantitative values are so far available. Here we study absorption saturation in films of two of the moststudied perovskites, La 0.7 Ca 0.3 MnO 3 (LCMO) and YBa 2 Cu 3 O 7 (YBCO), at the L 2,3 edge of Mn and Cu, respectively. By measuring the electron-yield intensity as a function of photon incidence angle and film thickness, the sampling depth d, photon attenuation length λ and the ratio λ/d have been independently determined between 50 and 300 K. The extracted sampling depth d LCMO ≈ 3 nm for LCMO at high temperatures in its polaronic insulator state (150 -300 K) is not much larger than values reported for pure transition metals (d Co or Ni ≈ 2 -2.5 nm) at room temperature, but is smaller than d YBCO ≈ 3.9 nm for metallic YBCO that is in turn smaller than the value reported for Fe 3 O 4 (d Fe3O4 ≈ 4.5 nm). The measured d LCMO increases to 4.5 nm when LCMO is in the metallic state at low temperatures. These results indicate that a universal rule of thumb for the sampling depth in oxides cannot be assumed, and that it can be measurably influenced by electronic phase transitions that derive from strong correlations.

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Section: Thin Film Characterizationmentioning

confidence: 99%

Electron sampling depth and saturation effects in perovskite films investigated by soft x-ray absorption spectroscopy

et al. 2014

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“…Our films show an increase of c when reducing the thickness (in agreement with films of ref. 15). Further examining the data of reference 15, one sees that while the first few layers at the interface exhibit c values larger than the STO one (cumulative displacement compared to c STO : ∆z positive and increasing), after about 3 monolayers c retrieves a value smaller than a = a STO (decreasing ∆z).…”

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confidence: 99%

“…For instance the dominating d z 2 occupation can be associated with only the first 2-3 ML (see T c or ∆z variation in the 9 ML film of ref. 15). In the next layers the e Mn g orbitals occupations start to relax toward a more balanced one as supported by the increase of both T c and conductivity as a function of the number of layers in 3 to 8 ML films.…”

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confidence: 99%

Interface Effects in Perovskite Thin Films

2012

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The control of matter properties (transport, magnetic, dielectric,. . . ) using synthesis as thin films is strongly hindered by the lack of reliable theories, able to guide the design of new systems, through the understanding of the interface effects and of the way the substrate constraints are imposed to the material. The present paper analyses the energetic contributions at the interfaces, and proposes a model describing the microscopic mechanisms governing the interactions at an epitaxial interface between a manganite and another transition metal oxide in perovskite structure (as for instance SrTiO3). The model is checked against experimental results and literature analysis.The technological importance of spin valves or spin injectors as potential applications of manganese oxides induced a large number of works on manganite thin films 2,3 . For this reason the lost of magnetization of La 2/3 Sr 1/3 MnO 3 (LSMO) or La 2/3 Ca 1/3 MnO 3 (LCMO) near an SrTiO 3 (STO) interface has been the subject of many interpretations. Let us cite (i) homogeneous substrate strain 4 (ii) electronic and/or chemical phase separation 5 related to structural inhomogeneities at the interface 6 , (iii) manganese e g orbital reconstruction inducing C-type antiferromagnetism 7,8 . None of these interpretations however provide a good understanding of the observed phenomena. For instance, it was shown that an homogeneous substrate strain of the in-plane parameters does not relax for film thickness smaller than 1000Å 5 , while a drastic change in the transport properties is observed for films thinner than a few unit cells (∼ 3 − 4 on STO substrate 7,9 , ∼ 30 on LaAlO 3 substrate 7 ,. . . ). In the second hypothesis (ii), there is no clear proposition of the nature of the inhomogeneities, their origin, the way they may act in order to induce the observed properties. Finally, ferromagnetic hysteresis loops were found in very thin films up to only three unit cells 9 (u.c.), in contradiction with the proposed C-type AFM ordering resulting from orbital ordering (iii). In any case, whatever the reasons put forward, the existence of a so-called "dead layer" at the interface between the manganite film and most perovskite substrates seems to be established 9,10 . This "dead layer" is of a few unit cells width and exhibits a large decrease of the conductivity ; however its origin is not at all understood.We believe that a careful analysis allow us to infer a model for the interface effects between a manganite and an oxide substrate with a perovskite structure. The main concepts of our model can be summarized as an energy balance at the interface.• It is well known that the strongest effect of the substrate is to constrain the film inplane cell parameters to fit the substrate ones. a film = a substrate b film = b substrate This constraint is quite strong since it is associated with bond elongation, i.e. the most energetic vibrational modes 11 . It thus relaxes slowly (not before 250 u.c., 1000Å, on a STO substrate 5 ). In the literature, it is associ...

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“…This offstoichiometry is accommodated by the introduction of extended defects and leads to a reduction of the magnetization and an increase of the resistivity such that the multilayers remain insulating at all temperatures. The laser fluence corresponding to the smaller spot size is typical for previous PLD-grown LSMO/STO multilayers (9,30), which might explain their inferior properties. Interdiffusion across the interface and off-stoichiometry in the LSMO layer such as that observed in Fig.…”

mentioning

confidence: 99%

Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers

Kourkoutis

Song

Hwang

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

139

123

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La 0.7 Sr 0.3 MnO 3 is a conducting ferromagnet at room temperature. Combined with thin SrTiO 3 layers, the resulting heterostructures could be used as highly spin-polarized magnetic-tunnel-junction memories. However, when shrunk to dimensions below an apparent critical thickness, the structures become insulating and ferromagnetic ordering is suppressed. Interface spin and charge modulations are thought to create an interfacial dead layer, thus fundamentally limiting the use of this material in atomic-scale devices. The thickness of this dead layer, and whether it is intrinsic, is still controversial. Here we use atomic-resolution electron spectroscopy to demonstrate that the degradation of the magnetic and transport properties of La 0.7 Sr 0.3 MnO 3 ∕SrTiO 3 multilayers correlates with atomic intermixing at the interfaces, and the presence of extended two-dimensional cation defects in the La 0.7 Sr 0.3 MnO 3 layers (in contrast to three-dimensional precipitates in thick films). When these extrinsic defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in five-unit-cell-thick manganite layers in superlattices, placing the upper limit for any intrinsic dead layer at two unit cells per interface.electron energy loss spectroscopy | manganites | scanning transmission electron microscopy C olossal magnetoresistance, metal-insulator transitions, charge/orbital ordering, and half-metal ferromagnetism are only some of the intriguing phenomena that occur in manganites and have driven interest in the family of perovskite manganese oxides (ABO 3 perovskite structure, B site occupied by Mn) (1). With a Curie temperature (T c ) of ∼370 K, the half-metal La 0.7 Sr 0.3 MnO 3 (LSMO) has been considered a promising candidate for spintronics applications. However, although complete spin polarization in LSMO was inferred from photoemission measurements (2) and a record tunneling magnetoresistance (TMR) ratio of 1,800% was obtained at low temperature in tunnel junctions with manganite electrodes separated by a thin insulating layer of SrTiO 3 (STO) (3), the TMR decreased rapidly as the temperature increased and diminished while still far below T c . One possible origin for the reduced TMR is the reduction of ferromagnetic ordering at the interface between the manganite and the STO. These interfacial effects have been suggested to be dominant as the LSMO layer thickness decreases, causing the magnetization and T c to degrade and the resistivity to increase, ultimately resulting in films that are insulating at all temperatures when the layer thickness decreases below a reported critical value of 7-13 unit cells (4-11). This critical thickness for sustaining conductivity below T c is attributed to an inherent "dead layer" at the interface between . One origin for the reduced T c and saturation magnetization of thin LSMO films compared to the bulk is believed to be a result of spin canting at the LSMO/STO interface (6, 15). Alternatively, magnetic phase separation into ferromagnetic metallic and less-ord...

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Structure determination of monolayer-by-monolayer grownLa1−xSrxMnO3thin films and the onset of magnetoresistance

Cited by 80 publications

References 37 publications

Electron sampling depth and saturation effects in perovskite films investigated by soft x-ray absorption spectroscopy

Electron sampling depth and saturation effects in perovskite films investigated by soft x-ray absorption spectroscopy

Interface Effects in Perovskite Thin Films

Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers

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