Phase separation in doped systems with spin-state transitions

Abstract

Spin-state transitions, observed in many transition metal compounds containing Co$^{3+}$ and Fe$^{2+}$, may occur with the change of temperature, pressure, but also with doping, in which case the competition of single-site effects and kinetic energy of doped carriers can favor a change in the spin state. We consider this situation in a simple model, formally resembling that used for manganites in Phys. Rev. Lett. 95, 267210 (2005). Based on such a model, we predict the possibility of a jump-like change in the number of Co$^{3+}$ ions undergoing spin-state transition caused by hole doping. A tendency to the electronic phase separation within a wide doping range is demonstrated. Phase diagrams with the regions of phase separation are constructed at different values of the characteristic parameters of the model.Comment: 9 pages, 5 figures, submitted to Phys. Rev.

Spin-state crossover and low-temperature magnetic state in yttrium-doped Pr0.7Ca0.3CoO3Knı́žek1, Hejtmánek2, Maryško3 et al. 2013Phys. Rev. B191130View full textAdd to dashboardCite

“…Recent DMFT calculations suggest also for this case a complex distribution of local cobalt valences and spin states [9], but with certain simplification, the metallic nature of these FM phases can be related to electron transfer between neighbors of the IS Co 3+ /LS Co 4+ or HS Co 3+ /HS Co 4+ kinds, eventually also LS Co 3+ /LS Co 4+ [10]. At least in the compositional region close above x c , the La 1−x Sr x CoO 3 systems seem to be dominated by a dynamic mixture of IS Co 3+ and LS Co 4+ and is described for illustration as the IS/LS phase.…”

Suppression of the metal-insulator transition by magnetic field in (Pr1−yYy)0.7Ca0.3CoO3 (y = 0.0625)

“…3 More recent dynamic mean field theory (DMFT) calculations thus suggest for La 1Àx Sr x CoO 3 a complex global state that can be locally understood as a dynamic fluctuation over different cobalt valences and spin states, 4 but with certain simplification, the metallic nature of these phases and their ferromagnetic ground state can be related to an electron transfer between neighbors of the IS-Co 3þ /LS-Co 4þ or HS-Co 3þ /HS-Co 4þ kinds, eventually also LS-Co 3þ /LS-Co 4þ . 5 To account for the magnetic properties actually observed, in particular, the low-temperature spontaneous moments and effective moments at intermediate temperatures, one may conclude on a domination of the IS-Co 3þ /LS-Co 4þ pairs in La 1Àx Sr x CoO 3 . 6 The situation is changed in systems in which the large La and Sr cations are substituted by smaller rareearth and calcium cations.…”

Evidence for Magnetic Polarons in Hole-Doped Cobalt Perovskites

“…After substantial experimental [4,5,10,[14][15][16][17][18][19][20][21][22] as well as theoretical [23][24][25] efforts in recent years, considerable progress has been achieved in understanding the physical properties of these compounds. It was shown that the electronic phase separation leading to formation of ferromagnetic (FM) clusters in a nonmagnetic matrix upon carrier injections plays a crucial role in their magnetic and transport properties.…”