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.
Theoretical model for the low-temperature ordering of Pr in PrBa 2 Cu3 O6+x
Theoretical model is presented to describe the anomalous ordered phase of Pr ions in PrBa_2Cu_3O_(6+x) below T_Pr = 12-17 K. The model considers the Pr multipole degrees of freedom and coupling between the Cu and Pr subsystems. We identify the symmetry allowed coupling of Cu and Pr ions and conclude that only an ab-plane Pr dipole ordering can explain the Cu spin rotation observed at T_Pr by neutron diffraction by Boothroyd et al. [A. T. Boothroyd et al., Phys. Rev. Lett. 78, 130 (1997)]. A substantial enhancement of the Pr ordering temperature is shown to arise from the Cu-Pr coupling which is the key for the anomalous magnetic behavior in PrBa_2Cu_3O_(6+x).
High-field magnetization process in ferrimagnetic R2Fe14C compounds-interplay of molecular and crystal fields
The magnetization process in magnetic fields up to 40 T of ferrimagnetic R2Fe14C compounds (R=Gd, Tb, Dy, Ho, Er, Tm) has been studied by considering the field-induced non-collinearity of the magnetic structure. Inter-sublattice molecular fields as well as the exchange coupling between 3d and 4f spins have been evaluated. The high-field susceptibility of Gd2Fe14C and Lu2Fe14C has been examined in detail. Magnetovolume phenomena are found to affect strongly the magnetic properties of these iron-based compounds.