VII AUSE Congress and II ALBA User's Meeting - 2015

Spin-lattice coupled anomalies and magneto-crystalline transition in Pr0.50Sr0.50CoO3 investigated by x-ray absoprtion spectroscopies

18 Jun 2015, 13:20

20m

Maxwell auditorium (ALBA Synchrotron)

Oral presentations II ALBA User's Meeting Session 7 - II ALBA User's Meeting 2015

Speaker

Ms Jessica Padilla-Pantoja (Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus Universitari de Bellaterra, E-08193, Bellaterra, Barcelona, Spain)

Description

The spin state of Co ions is a key degree of freedom in many *Ln*_1-x*A*_xCoO₃ (*Ln*: lanthanide, *A*:alkaline-earth) oxides with remarkable physical properties. In (Pr,*Ln*_1-x)Ca_xCoO₃ cobaltites near half-doped (x≈0.5), Co³⁺ spin-state sharp changes induce a first-order Pr³⁺ to Pr⁴⁺ valence shift and an exotic MIT. The insulating state is extraordinarily unleashed by electron transfer from Pr to Co sites, producing a volume contraction and stabilizing the diamagnetic Co³⁺ in LS state. Pr_0.50Sr_0.50CoO₃ (PSCO) notably differs from Pr_0.50Ca_0.50CoO_0.50 (PCCO). In contrast with the absence of long-range magnetic order in PCCO, metallic PSCO is FM below *T_C*≈230 K. Here, an unexpected step in magnetization at *T_S1*≈120 K was ascribed to changes in the magnetocrystalline anisotropy. This step may be positive or negative as a function of the applied field. The crystal symmetry reduction from orthorhombic to tetragonal at *T_S1*, with a significant local deformation of Co-O octahedra could be related to changes in the orbital moment *m_l*.However, the CoL_2,3 XMCD-derived *m_l* shows a monotonous behavior with temperature and no anomaly across *T_S1* . This contrasts with *m_s*, which presents an upward (downward) step on cooling at 100 (10) mT. This result thus points to a leading role of the spin-lattice coupling in this anomalous transition shown by PSCO. XAS and XES spectra also suggest Co³⁺ ions to be in a mixed spin state coexisting with predominantly low spin Co⁴⁺ ions, with an average spin state slightly larger than the one recently determined for PCCO.

References

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4. J. Padilla-Pantoja, J. Herrero-Martín, P. Gargiani, S. M. Valvidares, E. Pellegrin, A. Barla, and J. L. García-Muñoz, submitted.