Magnetic ordering in the JeffJ_{\rm eff} = 0 Nickelate NiRh2_2O4_4 prepared via a solid-state metathesis

In spinel-type nickelate NiRh$_2$O$_4$, magnetic ordering is observed upon the sample synthesized via kinetically controlled low-temperature solid-state metathesis, as opposed to previously-reported samples obtained through conventional solid-state reaction. Our findings are based on a combination of bulk susceptibility and specific heat measurements that disclose a N$\'e$el transition temperature of $T_N$ = 45 K in this material, which might feature spin-orbit entanglement in the tetragonally-coordinated $d^8$ Mott insulators. The emergence of magnetic ordering upon alteration of the synthesis route indicates that the suppression of magnetic ordering in the previous sample was rooted in the cation-mixing assisted by the entropy gain that results from high-temperature reactions. Furthermore, the $J_{\rm eff}$ = 0 physics, instead of solely the spin-only $S = 1$, describes the observed enhancement of effective magnetic moment well. Overseeing all observations and speculations, we propose that the possible mechanism responsible for the emergent magnetic orderings in NiRh$_2$O$_4$ is the condensation of $J_{\rm eff}$ = 0 exciton, driven by the interplay of the tetragonal crystal field and superexchange interactions.Comment: 7 pages, 5 figures, accepted in Physical Review Material

Linear Trimer Formation by Three-Center-Four-Electron Bonding in RuP

In molecules like hydrogen, most chemical bonds are formed by sharing two electrons from each atom in the bonding molecular orbital (two-center-two-electron (2c2e) bonding). There are, however, different kinds of chemical bonding. The I3- molecule, for example, is noteworthy because three iodine atoms are linearly united by sharing four electrons (three-center-four-electron (3c4e) bonding). Some inorganic solids undergo phase transitions that result in the formation of "molecules" in their crystalline frameworks, which are often accompanied by dramatic changes in physical properties; the metal-to-insulator transition (MIT) in vanadium dioxide, for example, occurs with the formation of dimer molecules with 2c2e bonding. We repot the creation of a linear ruthenium trimer with 3c4e bonding in ruthenium monopnictide at its MIT. Charge transfer from polymerized phosphorous to ruthenium produces this unusual molecule, with all conduction electrons trapped by the bonding molecular orbital. Our results demonstrate that molecules are crucial even in solid crystals as they impact their electronic properties.Comment: 12 pages, 9 figures, 3 Table

Superconductivity at 12 K in La2_2IOs2_2: a 5d metal with osmium honeycomb layer

We discovered superconductivity at $T_c$ = 12 K in a layered compound La$_2$IOs$_2$ with osmium honeycomb network. Despite heavy constituent elements unfavorable for phonon mediated mechanism, $T_c$ is the highest among lanthanoid iodides made of lighter elements such as La$_2$IRu$_2$ with $T_c$ = 4.8 K. Electronic anomalies are observed below 60 K similar to those observed in La$_2$IRu$_2$ below 140 K. La$_2$IOs$_2$ is a layered 5d electron system providing a platform to investigate the interplay between the electronic anomaly, superconductivity, and strong magnetic field.Comment: 7 pages, 4 figure