Phase transition in Pr0.5Ca0.5CoO3 and related cobaltites

Abstract

We present an extensive investigation (magnetic, electric and thermal measurements and X-ray absorption spectroscopy) of the Pr 0.5 Ca 0.5 CoO 3 and (Pr 1-y Y y ) 0.7 Ca 0.3 CoO 3 (y = 0.0625 -0.15) perovskites, in which a peculiar metal-insulator (M-I) transition, accompanied with pronounced structural and magnetic anomalies, occurs at 76 K and 40 -132 K, respectively. The inspection of the M-I transition using the XANES data of Pr

Spin-state crossover and low-temperature magnetic state in yttrium-doped Pr0.7Ca0.3CoO3Knı́žek1, Hejtmánek2, Maryško3 et al. 2013Phys. Rev. BSelf Cite191130View full textAdd to dashboardCite

“…11 an excellent fit can be obtained for g-factor of axial anisotropy, g = 5.86, g ⊥ = 1.25, irrespective the strength of applied field. Similar quasi-axial anisotropy of g-factor has been found in recent analysis of the Pr 4+ -related Schottky peaks in Pr 0.5 Ca 0.5 CoO 3 [14]. Important implications can be drawn from the analysis.…”

“…In the LS/LS ground state, the carrier concentation in the Co-O subsystem is thus reduced, in particular for the y = 0.15 sample down to 12% t 2g hole doping. Following the observed resistivity dependence down to 6 K, the actual regime of conduction is variable range hopping [14,18]. This means that the charge transport is realized via localized states close to Fermi level or, in other words, the doping level in the y = 0.15 sample is below the mobility edge for the t 2g band of LS/LS phase.…”

“…The decisive factor is, therefore, the exceptional closeness in energy of the two praseodymium states. The valence shift upon phase transition has been further confirmed and determined quantitatively by observation of the Pr 4+ related Schottky peak in heat capacity measurements [14] and by X-ray absorption spectroscopy at Pr L 3 edge [15,16]. In addition to the valence shift, a crossover from the IS or mixed LS/HS Co 3+ state to the LS states has been evidenced by drop of the paramagnetic susceptibility and by low values of effective moments below T MI , as well as by a detailed fit of the Co X-ray absorption and emission spectra [17].…”

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

“…11 It was found that the key to this specific MI-SS transition was a significant shift from mixed-valence Co 3þ /Co 4þ ions to pure Co 3þ ion, enabled by the simultaneous change in valence of some Pr 3þ ions into Pr 4þ ions. For the prototypical compound Pr 0.5 Ca 0.5 CoO 3 this valence shift was confirmed and determined quantitatively with the identification of the Pr 4þ -related Schottky peak in heat capacity measurements 12 and by X-ray absorption spectroscopy at the Pr L 3 edge. 13 Similar evidence was presented also for the Pr 0.7 Ca 0.3 CoO 3 systems doped by Y, [14][15][16] Sm, 17 and Tb.…”

“…We note that the jumps in electrical resistivity and magnetization actually observed do not represent the whole crossover as the phase evolution is not confined solely to temperatures near T MI-SS ; see, e. g., the smooth temperature dependence of the x-ray absorption nearedge structure (XANES) data at the Pr-L 3 edge for both the Pr 0.5 Ca 0.5 CoO 3 and (Pr 1Ày Y y ) 0.7 Ca 0.3 CoO 3 . 12,15 To explain this behaviour, we may refer to a model of the LS/HS crossover in a mean field approximation, presented in Ref. 22.…”