In addition, they present exceptional electronic and magnetic features related with the ability of Co ions to change their spin state as a function of temperature, applied pressure or laser excitation. This ingredient has a direct influence on unconventional conductivity and magnetic properties and makes them promising for spintronic applications. The unexpected spin-state-induced valence transitions of Pr and Co recently found by our team on (Pr,Ln,Ca-Sr)CoO3 cobaltites containing Pr are restimulating the field.
In this paper, which is the result of a collaboration between local staff at ALBA and ESRF synchrotron sources, and scientists from the Institute of Materials Science of Barcelona (ICMAB-CSIC), the authors extend their previous studies on an abrupt Pr-O hybridization in Pr0.5Ca0.5MnO3 (PCCO) to investigate Pr0.5Sr0.5CoO3 (PSCO). PSCO presents an anomalous magnetostructural transition at 120K, and the possible hybridization of Pr 4f and O 2 p states is discussed making use of different experimental techniques.
The complementary X-ray absorption spectroscopy (XAS) data recorded at the BOREAS and CLAESS beamlines served to complete the information provided by neutron diffraction, which had revealed unexpected structural/magnetic changes at TS= 120 K, and a strong contraction of some Pr-O bonds.
Surprisingly, while the Pr-O bonds contraction in the relative Pr0.5Ca0.5MnO3 oxide is accompanied by the striking appearance of Pr4+ at low temperatures as also shown by the same authors using XAS at Pr M4,5 edges in a recent work, soft and hard X-ray absorption spectra rule out any relevant thermally driven Pr ions electronic change in PSCO. Structural data do however point to an active participation of Pr ions to catalyze the transition (which vanishes replacing Pr by another lanthanide). Co L2,3 edge and O K edge XAS spectra confirm the stability of the Co spin-state below Ts, in contrast to the behavior of PCCO at low temperature. In view of the large density of empty t2g - symmetry states observed, the overall metallic behavior even below TS is attributed, in contrast to PCCO, to a (nearly temperature-independent) mixture of Co3+ ions in the intermediate- or high-spin configuration together with Co4+ ions in a low- or intermediate-spin state.
Fig. Left: Pr L3 edge XAS measured spectra of PSCO at T>TS and T<TS as compared to the calculated curve following multiple scattering theory. The inset shows a comparison between PCCO and PSCO in lowtemperature phases. Right: Pr L3 XAS of PSCO above and below TS as compared to a multiple-scattering theory calculation. In the inset the low T phase spectra of PSCO and PCCO are shown, where the large shoulder (B) in the latter around 5980 eV indicates the presence of Pr4+.
