Electron-doped La0.7A0.3CoO3-x Thin Films (A = Ce, Te) Studied by XAS

Pinta, C.; Fuchs, D.; Pellegrin, Eric; Adelmann, P.; Mangold, Stefan; Schuppler, S.

doi:10.1007/s10909-007-9321-1

Cited by 6 publications

(7 citation statements)

References 20 publications

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“…17 This result supports the conclusion that ferromagnetic order in LCO is due to strain induced suppression of the Jahn-Teller distortion that has been suggested to occur in bulk LCO. 5 However, existence of a Jahn-Teller distortion in bulk LCO has been called into question by recent studies.…”

supporting

confidence: 86%

Local atomic and electronic structures of epitaxial strained LaCoO3thin films

et al. 2012

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supporting

confidence: 86%

Local atomic and electronic structures of epitaxial strained LaCoO3thin films

et al. 2012

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“…Further, the ionic radius of Te 6+ has been reported to be between those of Co 3+(LS) and Co 3+(HS) (r Te 6+ = 0.56 Å, r Co 3+(LS) = 0.545 Å, r Co 3+(HS) = 0.61 Å), 32 suggesting size matching for Co-site substitution to minimize the difficulties accompanying local structural disorder. 33 The electrical resistivity (ρ) [symbols with lines in Fig. 2(a)] is also consistent with the tendency of electron-hole asymmetry.…”

Section: Introductionsupporting

confidence: 71%

Microscopic Examinations of Co Valences and Spin States in Electron-Doped LaCoO₃

et al. 2016

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We studied the Co valences and spin states in electron-doped LaCo1−yTeyO3 by measuring x-ray absorption spectra and electron spin resonance. The low-temperature insulating state involves the low-spin Co 3+ (S = 0) and the high-spin Co 2+ state, which is described by g = 3.8 and j eff = 1/2. The results, in concurrence with the electron-hole asymmetry confirmed in electrical resistivity, coincide with a spin-blockade phenomenon in this system. Further, we discuss the g factor in terms of the strong covalent-bonding nature and consider multiple origins of this phenomenon.

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“…This would still be consistent with EXAFS results. 46 This scenario appears plausible for another reason as well.…”

Section: Resultsmentioning

confidence: 99%

Suppression of the ferromagnetic state inLaCoO3films by rhombohedral distortion

Fuchs

Dieterle²,

Arac

et al. 2009

Phys. Rev. B

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Epitaxially strained LaCoO 3 (LCO) thin films were grown with different film thickness, t, on (001) oriented (LaAlO 3 ) 0.3 (SrAl 0.5 Ta 0.5 O 3 ) 0.7 (LSAT) substrates. After initial pseudomorphic growth the films start to relieve their strain partly by the formation of periodic nano-twins with twin planes predominantly along the <100> direction. Nano-twinning occurs already at the initial stage of growth, albeit in a more moderate way. Pseudomorphic grains, on the other hand, still grow up to a thickness of at least several tenths of nanometers. The twinning is attributed to the symmetry lowering of the epitaxially strained pseudo-tetragonal structure towards the relaxed rhombohedral structure of bulk LCO. However, the unit-cell volume of the pseudo-tetragonal structure is found to be nearly constant over a very large range of t. Only films with t > 130 nm show a significant relaxation of the lattice parameters towards values comparable to those of bulk LCO. 1Measurements of the magnetic moment indicate that the effective paramagnetic moment, m eff , and thus the spin state of the Co 3+ ion does not change for films with t ≤ 100 nm. However, the saturated ferromagnetic moment, m s , was found to be proportional only to the pseudo-tetragonal part of the film and decreases with increasing rhombohedral distortion. The measurements demonstrate, that ferromagnetism of LCO is strongly affected by the rhombohedral distortion while the increased unitcell volume mainly controls the effective paramagnetic moment and thus the spin state of the Co 3+ ion. 2 I. IntroductionThe perovskite-type lanthanum cobaltate LaCoO 3 (LCO) has recently attracted much attention due to its unusual electronic and magnetic properties at ambient pressure 1,2 and the observation of ferromagnetism in epitaxially strained thin films. 3,4 At low temperature, T ≤ 35 K, LCO is a nonmagnetic semiconductor with a ground state of Co 3+ ions in a low-spin (LS) configuration (t 2g 6 e g 0 , S = 0). 5,6 This is believed to change to a primarily intermediate-spin (IS) (t 2g 5 e g 1 , S = 1) state 7 in the temperature range 35 K < T < 100 K, and further to a mixture of IS and high-spin (HS) (t 2g 4 e g 2 , S = 2) states in the interval 300 K < T < 600 K. The crossover between spin states with increasing temperature arises from a delicate interplay between the crystal-field splitting, ∆ CF , between the t 2g and e g energy levels, and the intra-atomic exchange interaction (Hund`s rule coupling), ∆ EX . The balance between ∆ CF and ∆ EX can be affected by, e. g., hole or electron doping 8 and by chemical or external pressure. 910 Since ∆ CF is very sensitive to changes of the Co-O bond length, d, 11 and the Co-O-Co bond angle, γ , structural changes with respect to both easily modify the spin state of the Co 3+ ion. We have shown that the population of higher spin states is enhanced in tensile strained LCO films.3Calculations based on the generalized gradient approximation to the density functional theory indeed show that a magnetic state is more stable tha...

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Electron-doped La0.7A0.3CoO3-x Thin Films (A = Ce, Te) Studied by XAS

Cited by 6 publications

References 20 publications

Local atomic and electronic structures of epitaxial strained LaCoO3thin films

Local atomic and electronic structures of epitaxial strained LaCoO3thin films

Microscopic Examinations of Co Valences and Spin States in Electron-Doped LaCoO₃

Suppression of the ferromagnetic state inLaCoO3films by rhombohedral distortion

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Electron-doped La0.7A0.3CoO3-x Thin Films (A = Ce, Te) Studied by XAS

Cited by 6 publications

References 20 publications

Local atomic and electronic structures of epitaxial strained LaCoO3thin films

Local atomic and electronic structures of epitaxial strained LaCoO3thin films

Microscopic Examinations of Co Valences and Spin States in Electron-Doped LaCoO3

Suppression of the ferromagnetic state inLaCoO3films by rhombohedral distortion

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Microscopic Examinations of Co Valences and Spin States in Electron-Doped LaCoO₃