arXiv subjects

R. Cong

Publications and source records attributed to R. Cong.

5 recordsLinked to original sources

arXiv2025

From Bulk to Nanowire: A Dimensional Journey with CeIn$_3$

In this work, we have explored the Metallic-Flux Nanonucleation method to synthesize single crystals and nanowires (diameter $\approx$ 170 nm) of CeIn$_{3}$ and compare their properties. The effects of reduced dimensionality were systematically investigated using Energy Dispersive Spectroscopy (EDS), Selected area electron diffraction (SAED), magnetic susceptibility, heat capacity, and Nuclear Magnetic Resonance (NMR). Semi-quantitative EDS analysis revealed a Ce:In ratio of 1:3.1(1), and the SAED results confirmed that the nanowires are polycrystalline with a cubic unit cell. Magnetic susceptibility, specific heat, and NMR data indicated a suppression of the antiferromagnetic transition to $T_N$ $\approx$ 2.4 K compared to the bulk value ($\approx$ 10 K). Furthermore, NMR analysis at temperatures below 2.8 K showed a reduced quadrupole frequency, $\nu_Q$ $\approx$ 1.77(2) MHz, and provided evidence of polycrystalline nanowires formed within the nanoporous alumina template, in agreement with SAED results. We attribute these findings to an increasing magnetic order frustration induced by dimensionality in CeIn$_{3}$ nanowires.

cond-mat.str-el↗

arXiv2022

Effects of charge doping on Mott insulator with strong spin-orbit coupling, Ba$_2$NaOsO$_6$

The effects of doping on the electronic evolution of the Mott insulating state have been extensively studied in efforts to understand mechanisms of emergent quantum phases of materials. The study of these effects becomes ever more intriguing in the presence of entanglement between spin and orbital degrees of freedom. Here, we present a comprehensive investigation of charge doping in the double perovskite Ba$_2$NaOsO$_6$, a a complex Mott insulator where such entanglement plays an important role. We establish that the insulating magnetic ground state evolves from canted antiferromagnet (cAF)to N\'eel order for dopant levels exceeding ~ 10 %. Furthermore, we determine that a broken local point symmetry (BLPS) phase, precursor to the magnetically ordered state, occupies an extended portion of the (H-T) phase diagram with increased doping. This finding reveals that the breaking of the local cubic symmetry is driven by a multipolar order, most-likely of the antiferro-quadrupolar type.

cond-mat.str-el↗

arXiv2019

Evidence for orbital ordering in Ba$_2$NaOsO$_6$, a Mott insulator with strong spin orbit coupling, from First Principles

We present first principles calculations of the magnetic and orbital properties of Ba$_2$NaOsO$_6$ (BNOO), a 5$d^1$ Mott insulator with strong spin orbit coupling (SOC) in its low temperature emergent quantum phases. Our computational method takes into direct consideration recent NMR results that established that BNOO develops a local octahedral distortion preceding the formation of long range magnetic order. We found that the two-sublattice canted ferromagnetic ground state identified in Lu \etal, Nature Comm. {\bf 8}, 14407 (2017) is accompanied by a two-sublattice staggered orbital ordering pattern in which the $t_{2g}$ orbitals are selectively occupied as a result of strong spin orbit coupling. The staggered orbital order found here using first principles calculations asserts the previous proposal of Chen \etal, Phys. Rev. B {\bf 82}, 174440 (2010) and Lu \etal, Nature Comm. {\bf 8}, 14407 (2017), that two-sublattice magnetic structure is the very manifestation of staggered quadrupolar order. Therefore, our results affirm the essential role of multipolar spin interactions in the microscopic description of magnetism in systems with locally entangled spin and orbital degrees of freedom.

cond-mat.str-el↗

arXiv2017

Phase Diagram of Ba$_{2}$NaOsO$_{6}$, a Mott insulator with strong spin orbit interactions

We report $^{23}$Na nuclear magnetic resonance (NMR) measurements of the Mott insulator with strong spin-orbit interaction Ba$_{2}$NaOsO$_{6}$ as a function of temperature in different magnetic fields ranging from 7 T to 29 T. The measurements, intended to concurrently probe spin and orbital/lattice degrees of freedom, are an extension of our work at lower fields reported in Nat. Commun., v 8, 14407 (2017). We have identified clear quantitative NMR signatures that display the appearance of a canted ferromagnetic phase, which is preceded by local point symmetry breaking. We have compiled the field temperature phase diagram extending up to 29 T. We find that the broken local point symmetry phase extends over a wider temperature range as magnetic field increases.

cond-mat.str-el↗

arXiv2017

Hydrogen-modified inverse Spin Hall Effect in palladium-cobalt bi-layer films

The influence of hydrogen gas absorption by the Pd layer of bi-layered films containing Pd and Co layers on the inverse Spin Hall Effect (iSHE) in the material is measured. iSHE is driven by ferromagnetic resonance in the cobalt layer. In these conditions, the iSHE is seen as a d.c. voltage across the Pd layer. In the presence of hydrogen gas the iSHE peak shifts downwards in the applied field together with the ferromagnetic resonance absorption peak for the material. In parallel, an increase in the iSHE peak height and in its width is observed. Our analysis suggests that these observations can potentially be explained as a reduction in the spin Hall angle for the Palladium layer in the presence of hydrogen gas.

cond-mat.mtrl-sci↗