Temperature and composition dependence of crystal structures and magnetic and electronic properties of the double perovskitesLa2−xSrxCoIrO6

Abstract

X-ray, synchrotron, and neutron powder diffraction techniques were combined to investigate the evolution of crystal structure and physical properties of La 2−x Sr x CoIrO 6 with temperature and composition x. The following sequence of first-and second-order phase transitions is observed in this system, induced by increasing Sr content and temperature:The low-temperature magnetic structures are characterized by the propagation vector k = ͑0,0,0͒ for x =0, k = ͑1 / 2,0,1/ 2͒ for x = 1, and k = ͑0,1/ 2,1/ 2͒ or k = ͑1 / 2,0,1/ 2͒ for 1.5 and 2. Different noncollinear magnetic structures are concluded from the combination of magnetization measurements and neutron powder diffraction. Resistivity measurements reveal that the whole series behaves like nonmetals with electronic transport described by a combination of thermal activation and variable range hopping. Band gaps determined by electronic structure calculations agree very well with the experimental data for x = 0 and 1, and the calculated occupation of the d bands of Co and Ir are in good agreement with a transition IS/ HS-Co 2+ / LS-Ir 4+ → HS-Co 3+ / LS-Ir 5+ with increasing Sr content.

Charge Transfer and Structural Anomaly in Stoichiometric Layered Perovskite Sr2Co0.5Ir0.5O4

“…The average Ir–O distance in Sr 2 Co 0.5 Ir 0.5 O 4 of 1.95 Å (1.93 Å × 4 and 2.00 Å × 2) obtained from the Fourier transforms of the k 3 ‐weighted Ir‐ L 3 EXAFS data, is lower than the Ir 4+ –O distance of 2.02 Å in La 2 CoIrO 6 or in Sr 3 CoIrO 6 , and reflects a valence state of Ir higher than 4+. Therefore, from a crystallographic point of view, the most likely valence states of transition metal cations in Sr 2 Co 0.5 Ir 0.5 O 4 must correspond to Co 3+ and Ir 5+ (Figures and ).…”

Strong ferromagnetism induced by canted antiferromagnetic order in double perovskite iridates(La1−xSrx)2ZnIrO6Zhu1, Lu2, Wei3 et al. 2015Phys. Rev. B525120View full textAdd to dashboardCite

“…While there has been considerable work in exploring and understanding novel magnetic properties of other iridates (e.g., pyrochlores [14][15][16][17][18][19][20], honeycomb lattice [5,[21][22][23][24], and perovskites [25][26][27][28]), the highly localized double perovskites A 2 BIrO 6 have been much less intensively studied [29][30][31][32][33][34][35][36][37][38] and their magnetic properties remain to be fully understood. Using the prototypical La 2 ZnIrO 6 as an example, magnetic susceptibility measurement indicates a paramagnetic (PM)-to-ferromagnetic (FM)-like transition around 7.5 K [29,31], however, recent density functional theory calculations suggest that the low-temperature ground state should be canted antiferromagnetism instead of FM order [39].…”

Training-induced inversion of spontaneous exchange bias field on La1.5Ca0.5CoMnO6

“…From this class of materials, the perovskite-type (ABO 3 , A-rare/alkalineearth and B-TM) stands out. Ionic substitution at the A-site with cations of different charge and/or radii is a straightforward method to obtain interesting properties as glassy magnetic behavior 11 , structural/magnetic phase separation 12 , ferroelectricity 13 and also conventional and spontaneous exchange bias effects 9,10 . The La 2−x Sr x CoMnO 6 double-perovskite (DP) series exhibits the largest ZEB effect reported so far, for which 25% of Sr substitution at La site leads to the largest shift on the M (H) curve 11 .…”