X-ray and neutron scattering

Abstract:

The effect of uniaxial pressure on resistivity along the ab plane (ρab) and c axis (ρc) in single crystals of bilayer manganite La1.25 Sr1.75 Mn2 O7 has been investigated. A prominent finding is the asymmetric role of pressure on charge transport phenomenon. With increasing pressure along the c axis, ρab decreases and the metal-insulator (MI) transition temperature shifts towards higher temperature at the rate of 46 K GPa. In contrary to this, ρc increases and the MI transition temperature decreases with increasing pressure along the ab plane. The resistivity ratio ρc ρab is quite large, increases with pressure, and shows a peak at around the MI transition. We believe that the unusual behavior of transport properties is related to the Mn-O-Mn linkage between MnO2 layers and the spin reorientation from the c axis to the basal plane and vice versa with pressure. © 2006 The American Physical Society.

Abstract:

We have studied the magnetization of a series of spin-charge-ordered La2-x Srx Ni O4+δ single crystals with 0≤x≤0.5. For fields applied parallel to the ab plane there is a large irreversibility below a temperature TF1 ∼50 K and a smaller irreversibility that persists up to near the charge-ordering temperature. We observed memory effects in the thermoremnant magnetization across the entire doping range. We found that these materials retain a memory of the temperature at which an external field was removed and that there is a pronounced increase in the thermoremnant magnetization when the system is warmed through a spin reorientation transition. © 2006 The American Physical Society.

Abstract:

Total neutron scattering data from a powdered sample of MnO collected at 10 K have been analyzed using the reverse Monte Carlo method to refine the nuclear and magnetic structure. The results give the first unambiguous assignment of the average magnetic structure. The magnetic moments are aligned ferromagnetically within (111) sheets with the magnetization vectors of alternate sheets along axes parallel and antiparallel to the <112> directions, albeit with a small modulated out-of-plane component. Small displacements of Mn and O (modulated with the same periodicity) accompany the magnetic ordering and both atomic and magnetic structures may be described in the monoclinic space group C2.