Anomalous expansion and phonon damping due to the Co spin-state transition inRCoO3(R=La, Pr, Nd, and Eu)

Phase diagram and isotope effect in(Pr1−yEuy)0.7Kalinov1, Gorbenko2, Талденков3 et al. 2010Phys. Rev. BSelf Cite154200View full textAdd to dashboardCite

“…One can argue that due to the presence of lowspin Co 4+ , it would be indeed the IS state of Co 3+ , which is created close to a hole; 21,26,28 this would allow for a free motion of a hole within a cluster of LS Co 4+ and neighboring IS Co 3+ ions. 16,29,30 In the itinerant case, the stabilization of a J = 1 state due to spin-orbit interaction would also become questionable. Thus, based on these arguments, as well as on the results of Ref.…”

“…The most prominent example is LaCoO 3 , which was actively studied and controversially debated for more than 50 years. [5][6][7][8][9][10][11][12][13][14][15][16] It is generally agreed that Co 3+ ions in LaCoO 3 are in the LS state at low temperatures. Above approximately 25 K, a higher-spin state, either IS or HS, becomes thermally populated affecting various physical properties, e.g., magnetic susceptibility χ or thermal expansion α, which both exhibit pronounced peaks in their temperature dependence.…”

“…In some cases, especially if the system is close to a crossover between different states, an isotope substitution can drastically change the properties of the system. For example, in manganites, one can even induce a metal-insulator transition by substituting 16 O by 18 O. 35 Moreover, the isotope substitution can be also used for fine-tuning the behavior of a system, without stronger disturbances such as those caused, e.g., by doping (which introduce extra disorder).…”

“…Above approximately 25 K, a higher-spin state, either IS or HS, becomes thermally populated affecting various physical properties, e.g., magnetic susceptibility χ or thermal expansion α, which both exhibit pronounced peaks in their temperature dependence. [15][16][17] The susceptibility is naturally affected because the excited spin state (IS or HS) induces a significant increase in the magnetization. The thermal expansion is affected due to the different ionic radii: the LS Co 3+ ions with empty e g orbitals are significantly smaller than the IS or HS Co 3+ ions with partially filled e g orbitals.…”

“…17 In addition, with decreasing ionic radius in the lanthanide series, the structure changes from rhombohedral in LaCoO 3 to orthorhombic for R = Pr, Nd, and Eu. 16 The changes in the ionic radius can be also finetuned by mixing R elements with different ionic radii. In this situation, the partial substitution of R 3+ by a smaller R ′3+ in (R 1−y R ′ y ) 1−x A x CoO 3 systematically increases the chemical pressure, which should enhance the crystal field splitting and therefore stabilize the low-spin state.…”