X-ray and neutron scattering

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.

Abstract:

The structure of bilayer manganite LaSr2Mn2O7 has been investigated under high pressure using synchrotron and laboratory X-rays in the angle-dispersive X-ray diffraction geometry up to 35 GPa at ambient temperature. The Rietveld refinement results of the powder diffraction data show a crossover between the axial and equatorial Mn–O bond length values and a significant suppression of Jahn–Teller (JT) distortion around 16 GPa. Our results imply that a re-entrant behavior in LaSr2Mn2O7, which shows equality in all the three Mn–O bond length values around 16 GPa similar to ambient conditions, may dramatically alter the orbital ordering. Further, the P-V data for the bilayer compounds indicate that the additional substitution of La3+ for Sr2+ lowers the bulk modulus and enhances lattice softening.