Biomedical subjects

F Bridges

Publications and source records attributed to F Bridges.

At least 19 recordsLinked to original sources

PubMed2005

Universal relationship between magnetization and changes in the local structure of La1-xCaxMnO3: evidence for magnetic dimers.

We present extensive x-ray absorption fine structure measurements on La(1-x)Ca(x)MnO(3) as a function of the B field (to 11 T) and Ca concentration, chi(21%-45%). These results reveal local structure changes (associated with polaron formation) that depend only on the magnetization for a given sample, irrespective of whether the magnetization is achieved through a decrease in temperature or an applied magnetic field. Furthermore, the relationship between local structure and magnetization depends on the hole doping. A model is proposed in which a filamentary magnetization initially develops via the aggregation of pairs of Mn atoms involving a hole and an electron site. These pairs have little distortion and it is likely that they form at temperature T(*) above T(c).

Journal Article↗

PubMed2005

Local distortion induced metal-to-insulator phase transition in PrRu4P12.

Extended x-ray absorption fine structure (EXAFS) experiments have been carried out on PrRu(4)P(12) and PrOs(4)P(12) to study the metal-to-insulator (MI) phase transition in PrRu(4)P(12). No Pr displacement was observed across the MI transition temperature from the EXAFS data. Instead, our EXAFS data clearly show that a Ru displacement is associated with this MI transition. The very high Debye temperature for the Ru-P bond (Theta(D) = 690 K) suggests that a slight rotation/displacement of relatively rigid RuP(6) octahedra leads to this small Ru displacement, which accompanies the MI transition at 62 K in PrRu(4)P(12).

Journal Article↗

PubMed2002

Frustrated soft modes and negative thermal expansion in ZrW2O8.

Negative thermal expansion (NTE) in cubic ZrW2O8 has generated much interest due to its large, isotropic, and temperature independent behavior. Here, x-ray absorption fine structure data are presented for various atom pairs, providing evidence that the low-energy modes causing NTE correspond to the correlated vibrations of a WO4 tetrahedron and its three nearest ZrO6 octahedra. This involves translations of the WO4 as a rigid unit along each of the four <111> axes. The interconnectivity of these modes prevents an anisotropic soft mode from developing, a new geometrical phenomenon that we call the "frustrated soft mode."

Journal Article↗

PubMed2001

Magnetic-field modulation experiments on colossal magnetoresistance samples: first results.

Recently we have observed a small change in the width, sigma, of the Mn-O pair distribution function when a IT magnetic field is applied. To improve our sensitivity to magnetic-field-induced changes, we have developed a magnetic field modulation technique. At each X-ray energy we collect two data points, one with field on and the other with field off: as a result we collect two scans simultaneously. The difference in these two traces provides a measure of the magnetic-field-induced change. The results for the modulation measurements will be compared to the earlier work using static magnetic fields.

Calcium Compounds↗

PubMed1999