Magnetic Study of the Low-Temperature Anomalies in the Optimally Doped PrBCO Compound
The anomalous magnetic properties of a nonsuperconducting PrBa<sub>2</sub>Cu<sub>3</sub>O<sub>6+</sub> <inline-formula><tex-math notation="LaTeX">$_{x}$</tex-math></inline-formula> (or PrBCO) compound in an optimally doped oxygen state of concentration (<inline-formula><tex-math notation="LaTeX">$x= {\text{0.95}}$</tex-math> </inline-formula>) are investigated at low temperatures using magnetic measurements such paraprocess magnetic susceptibility <inline-formula><tex-math notation="LaTeX">$\chi _{{\text{H}}}(T)$</tex-math></inline-formula> under different values of a DC magnetic field <italic>H</italic> up to 8 T and isothermal magnetizations <inline-formula> <tex-math notation="LaTeX">$M_{{\text{T}}}(H)$</tex-math></inline-formula> with <italic>H</italic> up to 2.1 T. The temperature dependences of the derivatives of <inline-formula><tex-math notation="LaTeX">$\chi _{{\text{H}}}(T)$ </tex-math></inline-formula> indicate a significant decrease with increasing <italic>H</italic> of the Néel temperature <inline-formula><tex-math notation="LaTeX">$T_{{\text{N}}}= {\text{14}}\,{\text{K}}$</tex-math> </inline-formula> associated with antiferromagnetic (AFM) Pr ordering. The AFM-paramagnetic phase transition remains well defined even at 8 T, whereas the small anomaly at <inline-formula><tex-math notation="LaTeX">$T_{2}= {\text{10.5}}\,{\text{K}}$</tex-math></inline-formula>, which is due to the spin reorientation phase transition already reported before, seems clearly highlighted at 2 T but entirely suppressed above 6 T. A weak ferromagnetic (WFM) contribution is revealed below <inline-formula><tex-math notation="LaTeX">$T_{{\text{N}}}$</tex-math> </inline-formula> with more evidence particularly below the low critical point <inline-formula> <tex-math notation="LaTeX">$T_{{\text{cr}}}= {\text{4-5 K}}$</tex-math></inline-formula> whose anomaly is still visible with increasing <italic>H</italic> up to 8 T. Weak field-induced transitions between AFM and WFM phases are observed in the derivatives of <inline-formula><tex-math notation="LaTeX">$M_{{\text{T}}}(H)$</tex-math></inline-formula> at a low transition field (<inline-formula><tex-math notation="LaTeX">$H_{{\text{t}}}< {\text{1}}\,{\text{T}}$</tex-math> </inline-formula>). All results are discussed and compared with those found in previous works.
PSEUDODIPOLAR INTERACTION IN NONCOLLINEAR ANTIFERROMAGNETS AND SPIN WAVES IN PR2CUO4
Abstract There are tetragonal noncollinear antiferromagnets with sublattices which do not interact in the mean field exchange approximation (R2CuO4 family ( R = Pr, Nd, Sm, Eu ) U2Pd2X ( X = Sn, In ) PrBa2Cu3O6+x, etc.) Their noncollinear magnetic structure is explained assuming the pseudodipolar interaction (PDI). The spin waves of the copper subsystem in the R2CuO4 family are studied theoretically. The interplane PDI splits in-plane spin waves on acoustic and optical branches and the intraplane PDI gives rise to the in-plane spin-wave gap as a consequence of the interaction between spin waves. Neutron scattering data on Pr2CuO4 are presented and parameters of both intraplane and interplane PDI are determined. An analysis of the spin configuration in a canted magnetic field for R2CuO4 magnets is given and experimental evidence of the Bose–Einstein condensation of the uniform spin waves is presented.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%