Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSingle-crystal growth of the ternary BaFe$_2$As$_2$ phase using the vertical Bridgman technique
107
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Ternary Ba-Fe-As system has been studied to determine a primary solidification field of the BaFe$_2$As$_2$ phase. We found that the BaFe$_2$As$_2$ phase most likely melts congruently and primarily solidifies either in the FeAs excess or Ba$_{x}$As$_{100-x}$ excess liquid. Knowing the primary solidification field, we have performed the vertical Bridgman growth using the starting liquid composition of Ba$_{15}$Fe$_{42.5}$As$_{42.5}$. Large single crystals of the typical size 10x4x2 mm$^3$ were obtained and their quality was confirmed by X-ray Laue and neutron diffraction.
rate research
Read More
We report a simple, reliable method to grow high quality BaFe$_{2-x}$Co$_x$As$_2$ single crystal samples without using any fluxing agent. The starting materials for the single crystal growth come from well-crystallized polycrystalline samples and the highest growing temperature can be 1493 K. The as-grown crystals have typical dimensions of 4$times3times$0.5 mm$^3$ with c-axis perpendicular to the shining surface. We find that the samples have very large current carrying ability, indicating that the samples have good potential technological applications.
We have performed neutron diffraction measurement on a single crystal of parent compound of iron-based superconductor, BaFe$_2$As$_2$ at 12~K. In order to investigate in-plane anisotropy of magnetic form factor in the antiferromagnetic phase, the detwinned single crystal is used in the measurement. The magnetic structure factor and magnetic form factor are well explained by the spin densities consisting of $3d_{yz}$ electrons with a fraction of about 40~% and the electrons in the other four $3d$ orbitals with each fraction of about 15~%. Such anisotropic magnetic form factor is qualitatively consistent with the anisotropic magnetic behaviors observed in the antiferromagnetic phase of the parent compound of iron-based superconductor.
On experimental side, BaFe$_2$As$_2$ without doping has been made superconducting by applying appropriate pressure (2-6 GPa). Here, we use a full-potential linearized augmented plane wave method within the density-functional theory to investigate the effect of pressure on its crystal structure, magnetic order, and electronic structure. Our calculations show that the striped antiferromagnetic order observed in experiment is stable against pressure up to 13 GPa. Calculated antiferromagnetic lattice parameters are in good agreements with experimental data, while calculations with nonmagnetic state underestimate Fe-As bond length and c-axis lattice constant. The effects of pressure on crystal structure and electronic structure are investigated for both the antiferromagnetic state and the nonmagnetic one. We find that the compressibility of the antiferromagnetic state is quite isotropic up to about 6.4 GPa. With increasing pressure, the FeAs$_4$ tetrahedra is hardly distorted. We observe a transition of Fermi surface topology in the striped antiferromagnetic state when the compression of volume is beyond 8% (or pressure 6 GPa), which corresponds to a large change of $c/a$ ratio. These first-principles results should be useful to understanding the antiferromagnetism and electronic states in the FeAs-based materials, and may have some useful implications to the superconductivity.
Unconventional superconductivity arises at the border between the strong coupling regime with local magnetic moments and the weak coupling regime with itinerant electrons, and stems from the physics of criticality that dissects the two. Unveiling the nature of the quasiparticles close to quantum criticality is fundamental to understand the phase diagram of quantum materials. Here, using resonant inelastic x-ray scattering (RIXS) and Fe-K$_beta$ emission spectroscopy (XES), we visualize the coexistence and evolution of local magnetic moments and collective spin excitations across the superconducting dome in isovalently-doped BaFe$_2$(As$_{1-x}$P$_x$)$_2$ (0.00$leq$x$leq0.$52). Collective magnetic excitations resolved by RIXS are gradually hardened, whereas XES reveals a strong suppression of the local magnetic moment upon doping. This relationship is captured by an intermediate coupling theory, explicitly accounting for the partially localized and itinerant nature of the electrons in Fe pnictides. Finally, our work identifies a local-itinerant spin fluctuations channel through which the local moments transfer spin excitations to the particle-hole (paramagnons) continuum across the superconducting dome.
We measured resistivity and specific heat of high-quality CsFe$_2$As$_2$ single crystals, which were grown by using a self-flux method. The CsFe$_2$As$_2$ crystal shows sharp superconducting transition at 1.8 K with the transition width of 0.1 K. The sharp superconducting transition and pronounced jump in specific heat indicate high quality of the crystals. Analysis on the superconducting-state specific heat supports unconventional pairing symmetry in CsFe$_2$As$_2$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
