Quasi One-Dimensional Spin Fluctuations in YBa(2)Cu(3)O(6+x)

We study the spin fluctuation of the oxygen deficient planes of YBa(2)Cu(3)O(6+x). The Cu-O chains that constitute these planes are described by a model that includes antiferromagnetic interactions between spins and Kondo-like scattering of oxygen holes. The spectrum of magnetic excitations shows the presence of incommensurate dynamic fluctuations along the direction of the chains. The presence of itinerant holes is responsible for the existence of important differences between the spin dynamics of this system and that of a quasi-one-dimensional localized antiferromagnet. We comment on the possibility of experimental observation of these fluctuations.Comment: 22 pages, REVTEX, 3 figures, to appear in PRB55 (1May 1997

O. Gradenwitz, Fr. Bilabel, Β. Pfeiffer, A. Lauer, Heidelberger Konträrindex der Griechischen Papyrus-Urkunden

Hohlwein N. O. Gradenwitz, Fr. Bilabel, Β. Pfeiffer, A. Lauer, Heidelberger Konträrindex der Griechischen Papyrus-Urkunden. In: L'antiquité classique, Tome 2, fasc. 1, 1933. pp. 258-259

Temperature dependence of martensite structure and its effect on magnetic field induced strain in Ni2MnGa magnetic shape memory alloys

Structure in two Ni$_2$MnGa alloys, that exhibit large magnetic field induced strain in martensite phase, was studied with neutron diffraction in temperature range 4K-354K. It is found that lattice parameters in martensite notably change with temperature. The magnetic field induced strain value decreases/rises with the rise/decrease of temperature according to the change of (l-c/a) in martensite phase. The critical value of the magnetic field for activation of the twin's boundary motion decreases with increasing temperature

Approaches to modeling diffuse scattering from molecular crystals : Para-Terphenyl (C18H14)

Diffuse scattering is a probe of the local correlations in a crystal, whereas Bragg peaks are descriptive of the average long-range ordering. The long-range average is the result of numerous local configurations the population of which cannot be determined from the Bragg peaks. Diffuse scattering can examine this population. This is particularly the case when making use of the three-dimensional distribution of diffuse scattering from single crystals. However, diffuse scattering is very weak and broad and is often of similar intensity to the experimental background, which makes data collection demanding. Disorder can also take many forms and local configurations are not constrained by the average crystallographic symmetry. Here, three approaches to the modeling of diffuse scattering from molecular crystals will be discussed. All three approaches are based on a Monte Carlo (MC) simulation. As an example, the modeling of neutron diffuse scattering from para-terphenyl (PTP, C 18H14) will be described