Among all the rare earth elements, Pr is known to behave as a singularity in the high-Tc families. When high-temperature cuprates are doped with Pr the superconductivity is quenched, and a metal insulator transition occurs. The origin of this behavior, being of fundamental interest, may also shed light on the mechanism of high-temperature superconductivity, since any reasonable theory for this mechanism should explain the behavior of the Pr-based system. The physical properties and the several theories which have been proposed to describe the anomalous behavior of Pr-doped systems in the normal and superconducting states are reviewed.

The question of Pr in HTSC

Publisher Summary The muon spin rotation/relaxation/resonance (μSR) spectroscopy has become an important tool for probing local static and dynamic magnetic properties. In over two decades a quite substantial body of μSR data has been collected from rare-earth and actinide materials, the latter, however, mostly restricted to samples containing uranium. μSR is the measurement of the temporal development of the spatial orientation of the spins of muons, which have been implanted in the material of interest with all spins initially fixed in one direction (complete muon spin polarization). μSR can be performed either with positive or negative muons. The latter behave like heavy electrons and will be captured into Bohr orbits by the atoms in the sample material. They will quickly reach the ls ground state, whose orbital radius, however, is comparable to nuclear radii. Negative muons thus sense predominantly the effects of the protonic charge distribution and the result is primarily of interest to nuclear physics. The magnetic field at the site of the muon in a magnetic compound is, at least in part, created by the dipole moments on neighboring paramagnetic atoms or ions.

Chapter 206 μSR studies of rare-earth and actinide magnetic materials

(R = Pr, Sm, Eu, Gd, Dy, Y, Ho, Er, Tm) has been studied using complex chemical bond theory. The results indicated that with the decreasing of R radius, the ionicities for all considered types of bond decrease. This is in good agreement with the experimental fact that decreases with the decreasing of R radius. with no Ba-site Pr in this calculation is also predicted to be a superconductor. This supports the conclusion obtained by Blackstead et al. The ionicity for each bond obeys the following order: Ba - O > R - O > Cu(2) - O(1) > Cu(2) - O(2,3) > Cu(1) - O(4) Cu(1) - O(1).

https://iopscience.iop.org/article/10.1088/0953-8984/10/5/001/pdf

The bond ionicity in (R = Pr, Sm, Eu, Gd, Dy, Y, Ho, Er, Tm)

Heat capacity measurements on pure but twinned single crystals of reveal a sharp peak at , which according to thermal expansion, neutron diffraction, and magnetic susceptibility measurements originates from an antiferromagnetic ordering of the Pr-ion moments. A modest coupling to the Cu(2) spin system is observed. Below a first-order transition in the magnetic structure of the Pr spin system (at 13.4 K in warming; in cooling) is found. Field-dependent heat capacity data show anisotropic temperature dependences of the -peaks and recover a Schottky-like anomaly due to the crystal-field-split ground state of the .

https://iopscience.iop.org/article/10.1088/0953-8984/10/2/001/pdf

G. Fillion

Papers

Valence of praseodymium in PrxY1-xBa2Cu3O7- delta : Inelastic-neutron-scattering, specific-heat, and susceptibility study.