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.
Chapter 4 Field induced phase transitions in ferrimagnets
Publisher Summary This chapter discusses the high magnetic field magnetization processes in ferromagnetic compounds of the f–d type—that is, in compounds consisting of rare-earth and transition metal elements of the Fe group. The processes that are connected with the variation of mutual orientation of their magnetic sublattices and that reveal themselves through characteristic kinks and jumps in magnetization curves are focused in the chapter. Magnetic symmetry of a crystal changes when the orientation of magnetic sublattices spontaneously varies. A phase transition accompanied by a change of the magnetic symmetry takes place. The phase transitions are referred to as “field induced phase transitions” (FIPT) that may be of 1st or 2nd order. FITP connected with breaking of a collinear alignment of sublattices in ferrimagnetics are also considered in the chapter. It is assumed that the magnetic anisotropy of these materials is small in the sense that the energy of a magnetic anisotropy is smaller in comparison with the energy of the exchange interaction of sublattices. The magnetic anisotropy in such materials is best manifested near a compensation point, where critical fields of transitions to a canted phase tend to zero. In this connection, H–T phase diagrams are very complicate near Tc and composed of curves of the 1st and 2nd order phase transitions and of critical, tricritical points, and others.
Neutron and X-ray scattering studies of magnetism in non-superconducting PrBa2Cu3O6+x
Abstract I give a short review of neutron and X-ray scattering experiments undertaken to study the magnetic properties of non-superconducting PrBa 2 Cu 3 O 6+ x . The measurements have confirmed the magnetic ordering of the Pr sublattice at temperatures below T Pr ≈20 K, and have revealed an incommensurate magnetic structure with a long period (∼600 A) involving both the Pr and Cu spins. The Cu spins in this Pr ordered phase are found to be non-collinear. Taken as a whole, the results provide strong evidence for a substantial magnetic coupling of the pseudodipolar type between the Pr and Cu ions. The effect of this coupling is also evident in the spectrum of low energy magnetic excitations determined by neutron inelastic scattering.