Metallic conductivity in Na-deficient structural domain walls in the spin-orbit Mott insulator Na2IrO3

Honeycomb Na2IrO3 is a prototype spin-orbit Mott insulator and Kitaev magnet. We report a combined structural and electrical resistivity study of Na2IrO3 single crystals. Laue back-scattering diffraction indicates twinning with ±120◦ rotation around the c∗ axis while scanning electron microscopy displays nanothin lines parallel to all three b-axis orientations of twin domains. Energy dispersive x-ray analysis line scans across such domain walls indicate no change of the Ir signal intensity, i.e., intact honeycomb layers, while the Na intensity is reduced down to ∼2/3 of its original value at the domain walls, implying significant hole doping. Utilizing focused-ion-beam microsectioning, the temperature dependence of the electrical resistance of individual domain walls is studied. It demonstrates the tuning through the metal-insulator transition into a correlated-metal ground state by increasing hole doping

Thermal decomposition of the Kitaev material α−RuCl3 and its influence on low-temperature behavior

We explore the effect of heat treatment in argon atmosphere under various temperatures up to 500∘C on single crystals of α−RuCl3 by the study of the mass loss, microprobe energy-dispersive x-ray spectroscopy, powder x-ray diffraction, and electrical resistance, as well as low-temperature magnetic susceptibility and specific heat. Clear signatures of dechlorination and oxidation of Ru appear for annealing temperatures beyond 300∘C. Analysis of the specific heat below 2 K reveals a RuO2 mass fraction of order 1% for pristine α−RuCl3 which increases up to 20% after thermal annealing, fully consistent with mass-loss analysis. The small RuO2 inclusions drastically reduce the global electrical resistance and may thus significantly affect low-temperature thermal transport and Hall effect

Pressure-induced dimerization and collapse of antiferromagnetism in the Kitaev material α−Li2IrO3

We present magnetization measurements carried out on polycrystalline and single-crystalline samples of $\alpha$-Li$_2$IrO$_3$ under hydrostatic pressures up to 2 GPa and establish the temperature-pressure phase diagram of this material. The N\'eel temperature ($T_{\rm{N}}$) of $\alpha$-Li$_2$IrO$_3$ is slightly enhanced upon compression with $dT_{\rm{N}}/dp$ = 1.5 K/GPa. Above 1.2 GPa, $\alpha$-Li$_2$IrO$_3$ undergoes a first-order phase transition toward a nonmagnetic dimerized phase, with no traces of the magnetic phase observed above 1.8 GPa at low temperatures. The critical pressure of the structural dimerization is strongly temperature-dependent. This temperature dependence is well reproduced on the ab initio level by taking into account lower phonon entropy in the nonmagnetic phase. We further show that the initial increase in $T_{\rm{N}}$ of the magnetic phase is due to a weakening of the Kitaev interaction $K$ along with the enhancement of the Heisenberg term $J$ and off-diagonal anisotropy $\Gamma$. Our study reveals a common thread in the interplay of magnetism and dimerization in pressured Kitaev materials.Comment: 8 pages, 7 figure

Quantifying the influence of 3d–4s mixing on linearly coordinated metal-ions by L2,3-edge XAS and XMCD

The mixing valence d and s orbitals are predicted to strongly influence the electronic structure of linearly coordinated molecules, including transition metals, lanthanides and actinides. In specific cases, novel magnetic properties, such as single-ion magnetic coercivity or long spin decoherence times, ensue. Inspired by how the local coordination symmetry can engender such novel phenomena, in this study, we focus our attention on dopants (Mn, Fe, Co, Ni, Cu) in lithium nitride to accept innovation from molecular magnetism in a high symmetry P6/mmm solid-state crystal. The linear coordination environment results in strong 3d–4s mixing, proving to be an ideal series to investigate the role of d–s mixing and bonding on electronic structure and magnetism. It is shown that L2,3-edge XAS can be applied to experimentally identify the presence of 3d–4s mixing and the influence this has on the ligand-field splitting. XMCD specifies how spin–orbit coupling is affected. The combined spectroscopies are analysed to determine the effect of 4s mixing with support from ab initio calculations. The results provide new insight of relevance to future applications, including quantum information processing and the sustainable replacement of rare earths in magnets