Detailed relationship between local structure, polarons, and magnetization forLa1−xCaxMnO3

Abstract

We present detailed local structure measurements ͑using the extended x-ray absorption fine structure tech-nique͒ for the colossal magnetoresistive material La 1−x Ca x MnO 3 ͑0.21Ͻ x Ͻ 0.45͒ as a function of temperature and magnetic field. The local distortions of the Mn-O bonds are parameterized using , the width of the Mn-O pair-distribution function ͑PDF͒. After subtracting thermal phonon contributions, we show that the contributions to 2 from polaron and Jahn-Teller ͑JT͒ distortions, JT/polaron 2 , are a universal function of the magnetization, independent of how the magnetization is achieved via changes in temperature or magnetic field. However this universal behavior is only observed for B fieldsՆ 2 T, likely as a result of domain canting in low B fields. The resulting curve is well described by two straight lines with significantly different slopes. These regimes represent two distinctly differ distortions of the oxygen octahedra about the Mn. For low magnetizations up to ϳ65% of the theoretical maximum magnetization, M T , the slope is low and the distortion removed as the sample becomes magnetized is small-we argue this arises from polarons which have a low distortion around two ͑or possibly three͒ Mn sites. At high magnetizations large distortions per Mn site are removed as these sites become magnetized. The data are also analyzed in terms of a two Mn-O peak distribution using experimental standards for Mn-O. The results agree well with recent neutron PDF results but not with some earlier results. We discuss the limitations of assuming a two peak distribution in view of the two distortions needed to describe the Mn-O distortions as a function of T and B for B Ն 2 T. It is likely that there is a distribution of longer bonds. Finally we show that with increasing B field, the Mn-Mn peak also has a small B-field-induced change-a measure at the unit cell level of magnetostriction but find that there is no observable B-field-induced change in the Mn-La/Ca pair distribution for fields up to ϳ10 T.

Transport, electronic, and structural properties of nanocrystalline CuAlO2delafossites

“…showing the same trend in the modification of the width of the pair-distribution function (σ 2 ) and of the interatomic distances. 51 On the contrary, our results indicate that the next-neighbor Cu environment is similar in all the samples. The sintering temperature affects the disorder of further coordination shells lying in the plane perpendicular to the O-Cu-O bond.…”

A novel organic pollutants gas sensing material p-type CuAlO 2 microsphere constituted of nanoparticles for environmental remediation

“…Table 1 shows the fitting results of Cu K edge EXAFS spectra that correspond to the first coordination shell (Cu O). As can be observed, the Cu O mean bond length of both samples obtained from EXAFS results are similar to the literature obtained from XRD measurements [34]. The difference observed in the intensity of first peak of FT intensity between the two samples is due to the high degree of disorder (Debye-Waller factor ( )) in the CuAlO 2 compared to the Cu 2 O compound.…”

Spontaneous magnetization aboveTCin polycrystallineLa0.7Ca0.3MnO3Turcaud1, Pereira2, Sandeman3 et al. 2014Phys. Rev. B394191View full textAdd to dashboardCite

“…Later Lynn et al demonstrated the existence of a polaron glass phase characterized by short-range polaron correlations, present above T C [16]. In 2008, de Souza et al [17] suggested that the Griffiths-like treatment is inappropriate and a proper description should incorporate the formation of magnetic polarons (manifest as ferromagnetic clusters organized in Mn-spin dimers [18]) coalescing over the temperature range between T * and T C . In order to shed light on the origin of the ordering temperature T * , we have performed a detailed study comparing the magnetic, electronic, and structural properties of La 0.7 Ca 0.3 MnO 3 (orthorhombic LCMO) and La 0.7 Ba 0.3 MnO 3 (rhombohedral LBMO).…”