Magnetic Phase Separation inLa1−xSrxCo

Abstract

59Co NMR measurements on La1-xSrxCoO3 reported here establish unequivocally, for the first time, the coexistence of ferromagnetic regions, spin-glass regions, and hole-poor low spin regions at all x values from 0.1 to 0.5. A zero external field NMR spectrum, which is assigned to the ferromagnetic regions, has a spectral shape that is nearly x independent at 1.9 K, as are the relaxation times, T1 and T2. The integrated spectral area increases rapidly with x up to x = 0.2 and then decreases slightly for larger x. In a field of 9.97 T, a narrow NMR line is observed at 102 MHz, identical to that found in x = 0 samples in previous work. The integrated intensity of this spectrum decreases rapidly with increasing x, and is ascribed to hole-poor low spin regions. Beneath this spectrum, a third broad line, with a peak at 100 MHz, is assigned to a spin- or cluster-glass-like phase.

The Role of Structural and Compositional Heterogeneities in the Insulator-to-Metal Transition in Hole-Doped APd3O4 (A = Ca, Sr)

“…In addition to local distortions, any potential Na clustering may result in poorer fits to the local structure. A two phase fit including the possibility of a Na 2 CO 3 impurity was attempted, as some amount of Na 2 CO 3 was observed in solid state 23 Na NMR (see next section), though it did not improve the fit or capture the observed peak shoulder.…”

“…23 Na is a spin 3/2 quadrupolar nucleus in 100% abundance, making it an attractive nucleus to study in the materials before and 23 Na solid-state single pulse magic angle spinning NMR spectra (9.4 T, MAS at 8 kHz) showing a principle single peak corresponding to the single site in the crystal structure with a potential minor impurity on the right edge of the peak marked by (*). (c) Resistivity vs. temperature for a pressed pellet of NaPd 3 O 3 showing the highly metallic nature of this hole-doped oxide.…”

“…an isolated Na in the APd 3 O 4 matrix. The Figure 10: Single-pulse solid-state 23 Na MAS NMR spectra (9.4 T, MAS at 8 kHz) of Nasubstituted CaPd 3 O 4 and SrPd 3 O 4 . All of the Ca and Sr samples show 2 distinct Na environments represented by a sharp peak at 7 ppm and a broad signal centered around −10 ppm which grows relative to the sharp peak with increasing Na substitution.…”

“…21 Furthermore, complex palladium oxides are typically diamagnetic, allowing for more detailed studies of local structural changes throughout insulator-to-metal transitions with the use of solid-state NMR, which, while useful in examining local phase separation, is difficult to utilize in magnetic oxide materials. 22,23 Recently, we have observed a high Seebeck coefficient with metallic conductivity in the complex palladium oxide PbPdO 2 when it undergoes an insulator-to-metal transition with Li-substitution. 24 A better understanding of the insulator-to-metal transitions can lead to improvements in the functional properties of these and other oxide materials.…”

Low-Frequency Mechanical Spectroscopy of Lanthanum Cobaltite Based Mixed Conducting Oxides

“…Thus, the frustration may exist in the FM region even at temperatures close to Tc so that the whole system is not in a true ferromagnetic state. In fact, a coexistence of a hole-rich ferromagnetic phase and a holepoor cluster glasslike phase have been suggested below Tc by nMR and ac magnetic studies [27,28]. Considering these results, it is tentatively suggested that the whole system is inhomogeneous at the temperature below Tc and there are some hole-poor clusters.…”