Quantum paramagnetism in a non-Kramers rare-earth oxide: Monoclinic $\mathrm{P}{\mathrm{r}}_2\mathrm{T}{\mathrm{i}}_2{\mathrm{O}}_7$

Abstract

Little is so far known about the magnetism of the ${\mathrm{A}}_2{\mathrm{B}}_2{\mathrm{O}}_7$ monoclinic layered perovskites that replace the spin-ice supporting pyrochlore structure for $r_A/r_B>1.78$. We show that high quality monoclinic Pr${}_2$Ti${}_2$O${}_7$ single crystals with a three-dimensional network of non-Kramers Pr${}^{3+}$ ions that interact through edge-sharing super-exchange interactions, form a singlet ground state quantum paramagnet that does not undergo any magnetic phase transitions down to at least 1.8 K. The chemical phase stability, structure, and magnetic properties of the layered perovskite Pr${}_2$Ti${}_2$O${}_7$ were investigated using x-ray diffraction, transmission electron microscopy, and magnetization measurements. Synthesis of polycrystalline samples with the nominal compositions of Pr${}_2$Ti${}_{2+x}$O${}_7$ ($-0.16\le x\le 0.16$) showed that deviations from the Pr${}_2$Ti${}_2$O${}_7$ stoichiometry lead to secondary phases of related, structures including the perovskite phase Pr${}_{2/3}$TiO${}_3$ and the orthorhombic phases Pr${}_4$Ti${}_9$O${}_{24}$ and Pr${}_2$TiO${}_5$. No indications of site disordering (stuffing and anti-stuffing) or vacancy defects were observed in the Pr${}_2$Ti${}_2$O${}_7$ majority phase. A procedure for growth of high-structural-quality, stoichiometric single crystals of Pr${}_2$Ti${}_2$O${}_7$ by the traveling solvent floating zone (TSFZ) method is reported. Thermo-magnetic measurements of single-crystalline Pr${}_2$Ti${}_2$O${}_7$ reveal an isolated singlet ground state that we associate with the low symmetry crystal electric field environments that split the $2J+1=9$-fold degenerate spin-orbital multiplets of the four differently coordinated Pr${}^{3+}$ ions into 36 isolated singlets resulting in an anisotropic temperature independent van-Vleck susceptibility at low $T$. A small isotropic Curie term is associated with 0.96(2)\% non-interacting Pr${}^{4+}$ impurities.

18 pages, 7 figures, 6 tables

References in corpus (5)

• Dirac Strings and Magnetic Monopoles in Spin Ice Dy2Ti2O7
• Disordered Route to the Coulomb Quantum Spin Liquid: Random Transverse Fields on Spin Ice in Pr${}_2$Zr${}_2$O${}_7$
• Impact of Stoichiometry of Yb2Ti2O7 on its Physical Properties
• Synthesis, floating zone crystal growth and characterization of the Quantum Spin Ice $\mathrm{P}{\mathrm{r}}_2\mathrm{Z}{\mathrm{r}}_2{\mathrm{O}}_7$ pyrochlore
• Dynamical scaling as a signature of multiple phase competition in Yb${}_2$Ti${}_2$O${}_7$