Cooperative Jahn-Teller distortion in PrO2
Physical Review B - Condensed Matter and Materials Physics 70:2 (2004)
Abstract:
We report neutron diffraction data on single crystal PrO2 which reveal a cooperative Jahn-Teller distortion at TD=120±2 K. Below this temperature an internal distortion of the oxygen sublattice causes the unit cell of the crystallographic structure to become doubled along one crystal axis. We discuss several possible models for this structure. The antiferromagnetic structure below TN=13.5 K is found to consist of two components, one of which shares the same doubled unit cell as the distorted crystallographic structure. We also present measurements of the magnetic susceptibility, the specific heat capacity, and the electrical conductivity of PrO2. The susceptibility data show an anomaly at a temperature close to TD. From the specific heat capacity data we deduce that the ground state is doubly degenerate, consistent with a distortion of the cubic local symmetry. We discuss possible mechanisms for this. The conductivity shows an activated behavior with an activation energy Ea=0.262±0.003 eV.Field-induced magnetic and structural domain alignment in PrO2
Physical Review B - Condensed Matter and Materials Physics 70:2 (2004)
Abstract:
We present a neutron diffraction study of the magnetic structure of single crystal PrO2 under applied fields of 0-6 T. As the field is increased, changes are observed in the magnetic Bragg intensities. These changes are found to be irreversible when the field is reduced, but the original intensities can be recovered by heating to T> 122 K, then recooling in zero field. The antiferromagnetic ordering temperature TN=13.5 K and the magnetic periodicity are unaffected by the applied field. We also report measurements of the magnetic susceptibility of single crystal PrO2 under applied fields of 0-7 T. These show strong anisotropy, as well as an anomaly at T=122±2 K, which coincides with the temperature T D=120±2 K, at which a structural distortion occurs. For fields applied along the [100] direction the susceptibility increases irreversibly with field in the temperature range TNStripe order and magnetic transitions in La2-x Sr x NiO4
Physical Review B - Condensed Matter and Materials Physics 70:2 (2004)
Abstract:
Magnetic order has been investigated in stripe-ordered La 2-xSrxNiO4 (x=0.275,0.37,0.4) by dc magnetization and by polarized- and unpolarized-neutron diffraction. In the magnetically ordered phase, all three compositions exhibit a magnetic transition consistent with a spin reorientation in the ab plane. For x=0.37, the spin axes rotate from an angle of 37.7°±0.3° to the stripe direction at 71 K, to 52.3°±0.20 at 2 K. The x=0.275 and 0.4 compounds were found to undergo a similar spin reorientation. A spin reorientation has now been observed to occur for five different doping levels in the range of 0.275≤x≤0.5, suggesting that this spin transition is an intrinsic property of the stripe phase.Neutron powder diffraction and total scattering studies of α- quartz-type piezoelectric materials at high temperature
Physica B Condensed Matter Elsevier 350:1-3 (2004) e979-e981
Critical behavior dependence on Sr concentration in La1-xSrxMnO3
J APPL PHYS 95:11 (2004) 7366-7368