Valence change of praseodymium in Pr0.5Ca0.5CoO3investigated by

Abstract

X-ray absorption spectroscopy measurements in Pr 0.5 Ca 0.5 CoO 3 were performed at the Pr M 4,5 , Pr L 3 , and Ca L 2,3 absorption edges as a function of temperature below 300 K. Ca spectra show no changes down to 10 K while a noticeable thermally dependent evolution takes place at the Pr edges across the metal-insulator transition. Spectral changes are analyzed by different methods, including multiple scattering simulations, which provide quantitative details on an electron loss at Pr 4f orbitals. We conclude that in the insulating phase a fraction [15(±5)%] of Pr 3+ undergoes a further oxidation to adopt a hybridized configuration composed of an admixture of atomiclike 4f 1 states (Pr 4+ ) and f-symmetry states on the O 2p valence band (Pr 3+ L states) indicative of a strong 4f-2p interaction.

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

“…The existence of Pr→CoO 3 electron transfer was supported later theoretically by GGA+U electronic structure calculations exploiting the temperature dependence of the structural experimental data for Pr 0.5 Ca 0.5 CoO 3 [7], and experimentally, in particular by observation of Schottky peak in the low temperature specific heat, related to Zeeman splitting of the ground doublet of Kramers ions Pr 4+ [8]. The direct proof of the mixed Pr 3+ /Pr 4+ valence, was provided for Pr 0.5 Ca 0.5 CoO 3 using the Pr L 3 and M 4,5 edge X-ray absorption spectroscopy (XAS) by Garcia-Munoz et al and Herrero-Martin et al [9,10], demonstrating also the spin change on cobalt sites by means of the Co K and L edge spectroscopies [11]. Using the measurement of the temperature dependence of the X-ray absorption near-edge structure (XANES) spectra at the Pr L 3 edge on on crossing the M-I transition.…”

Electrical resistivity anomaly in (Pr1−yMy)1−xCaxCoO3 epitaxial films (M=Y, Gd) fabricated by pulsed laser deposition

“…The theoretical hypothesis about the crucial role of variable praseodymium valence was experimentally supported by the observations of a Schottky peak in the low temperature specific heat of (Pr 1−y Y y ) 0.7 Ca 0.3 CoO 3 ( y=0.075 and 0.15), 12 and by the x-ray absorption near-edge structure (XANES) spectra at the Pr L 3 edge directly. [13][14][15][16] It is widely desirable to use a single crystal or an epitaxial film for the physical investigation. In the La 1−x Sr x CoO 3 system, single crystals and thin films have been fabricated and investigated.…”

Magnetostructural coupling, magnetic ordering, and cobalt spin reorientation in metallicPr0.5Sr0.5CoO

“…The appearance of the 4-fold tetragonal axis brings on degeneration and two equivalent magnetic easy-axes, which are associated to the two conjugated magnetic domains with spin orientations [110] and [1][2][3][4][5][6][7][8][9][10]. Therefore, the loss of magnetization (negative step) under low fields (H< H cr ) is produced by the presence of conjugated [110] and [1][2][3][4][5][6][7][8][9][10] ferromagnetic domains after the Imma → I4/mcm transition. A schematic view of magnetic ordering and magnetic domains above and below T S1 is shown in Figure 9.…”

“…[1][2][3][4] In this context, the physical properties of half-doped Pr-based Pr 0.50 A 0.50 CoO 3 specimens are attracting the interest due to the observation of nonconventional phase transitions and distinct unexpected properties with A=Ca 4-11 and Sr. [12][13][14][15][16][17][18] In this way, Ca valence shift. [7][8][9] Pr 0.50 Ca 0.50 CoO 3 (PCCO) is orthorhombic (Pnma) and metallic but it becomes insulating at T MI ~ 80 K. An electron is transferred from some Pr atoms to Co sites [6][7][8][9][10] and a concomitant SS crossover promotes the stabilization of the Co 3+ low spin (LS) state. 10 Remarkably, PCCO exhibits exceptional photoresponse capabilities of potential interest for ultrafast optical switching devices.…”