Dimer Crystallization Induced by Elemental Substitution in the Honeycomb Lattice of Ru1-xOsxCl3

TL;DR

This study explores how substituting Os for Ru in RuCl3 influences its magnetic phases, revealing a rich phase diagram with antiferromagnetic, dimerized, and short-range ordered states driven by elemental substitution.

Contribution

It demonstrates that elemental substitution induces dimerization and complex magnetic phases, providing a rare example of molecular orbital crystallization in a disordered honeycomb lattice.

Findings

Dimerization occurs in the spin-singlet phase at certain compositions.

A rich phase diagram includes antiferromagnetic, dimer, and short-range order phases.

Elemental substitution triggers molecular orbital crystallization.

Abstract

Substitution effects of Os for Ru in {\alpha}-RuCl3 are investigated in a wide composition range of 0 =< x =< 0.67 in Ru1-xOsxCl3 by X-ray and electron diffraction, magnetic susceptibility, heat capacity, and Raman spectroscopy measurements. Apart from the Kitaev physics with antiferromagnetic interactions increasing with x, a rich phase diagram is obtained, which includes an antiferromagnetic long-range order below 12 K for x =< 0.15, a dome-shaped spin-singlet dimer phase below 130 K for 0.15 =< x =< 0.40, and a magnetic short-range order for x > 0.40. A dimerization as similarly observed in {\alpha}-RuCl3 under high pressure occurs in the spin-singlet phase. It is suggested that Ru-Os pairs in the solid solutions tend to form dimers with short bonds and trigger the first-order transition in the presence of pseudo-threefold rotational symmetry for dimerization around a substituted Os atom only at low substitutions. This is a rare example of molecular orbital crystallization induced by elemental substitution in a highly disordered system. The short-range order at high substitutions may be related to a random-singlet state stabilized by bond disorder in the honeycomb net.