Coexistence of Ferromagnetic and Stripe Antiferromagnetic Spin Fluctuations in SrCo_{2}As_{2}

Resonant inelastic soft x-ray scattering on LaPt2Si2

X-ray absorption and resonant inelastic x-ray scattering spectra of LaPt₂Si₂single crystal at the Si 2pand La 4dedges are presented. The data are interpreted in terms of density functional theory, showing that the Si spectra can be described in terms of Sisanddlocal partial density of states (LPDOS), and the La spectra are due to quasi-atomic local 4fexcitations. Calculations show that Ptd-LPDOS dominates the occupied states, and a sharp localized Lafstate is found in the unoccupied states, in line with the observations.

New Compounds and Phase Selection of Nickel Sulfides via Oxidation State Control in Molten Hydroxides

Molten salts are promising reaction media candidates for the discovery of novel materials; however, they offer little control over oxidation state compared to aqueous solutions. Here, we demonstrated that when two hydroxides are mixed, their melts become fluxes with tunable solubility, which are surprisingly powerful solvents for ternary chalcogenides and offer effective paths for crystal growth to new compounds. We report that precise control of the oxidation state of Ni is achievable in mixed molten LiOH/KOH to grow single crystals of all known ternary K-Ni-S compounds. It is also possible to access several new phases, including a new polytope of β-K₂Ni₃S₄, as well as low-valence KNi₄S₂ and K₄Ni₉S₁₁. KNi₄S₂ is a two-dimensional low-valence nickel-rich sulfide, and β-K₂Ni₃S₄ has a hexagonal lattice. Moreover, using KNi₄S₂ as a template, we obtained a new layered binary Ni₂S by topotactic deintercalation of K. The new binary Ni₂S has a van der Waals gap and can function as a new host layer for intercalation chemistry, as demonstrated by the intercalation of LiOH between its layers. The oxidation states of low-valence KNi₄S₂ and Ni₂S were studied using X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. Density functional theory calculations showed large antibonding interactions at the Fermi level for both KNi₄S₂ and Ni₂S, corresponding to the flat-bands with large Ni-d_x²-y² character.

Magnetic order and fluctuations in the quasi-two-dimensional planar magnet Sr(Co1-xNix)2As2

We use neutron scattering to investigate spin excitations in Sr ( Co 1 - x Ni x ) 2 As 2 , which has a c -axis incommensurate helical structure of the two-dimensional (2D) in-plane ferromagnetic (FM) ordered layers for 0.013 ⩽ x ⩽ 0.25 . By comparing the wave vector and energy dependent spin excitations in helical ordered Sr ( Co 0.9 Ni 0.1 ) 2 As 2 and paramagnetic SrCO 2 As 2 , we find that Ni doping, while increasing lattice disorder in Sr ( Co 1 - x Ni x ) 2 As 2 , enhances quasi-2D FM spin fluctuations. However, our band structure calculations within the combined density functional theory and dynamic mean field theory (DFT+DMFT) failed to generate a correct incommensurate wave vector for the observed helical order from nested Fermi surfaces. Since transport measurements reveal increased in-plane and c -axis electrical resistivity with increasing Ni doping and associated lattice disorder, we conclude that the helical magnetic order in Sr ( Co 1 - x Ni x ) 2 As 2 may arise from a quantum order-by-disorder mechanism through the itinerant electron mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions.

Synthesis and magnetic properties in quaternary Ca1-xPrxCo2As2single crystals

Series of Ca1-xPrxCo2As2(x= 0, 0.10, 0.25, 0.4, 0.6, 0.75, 0.85, 1) single crystals have been synthesized in order to clarify the variation of magnetic order from antiferromagnetic (AFM) in CaCo2As2to ferromagnetic (FM) in PrCo2As2. It is found that the lattice constant ofc-axis are contracted with the introduction of Pr into Ca sites in CaCo2As2. Electronic transport measurements reveal the metallicity in this system. Systematic magnetic measurements and analysis show that substituting only 10% of Pr for Ca changes the magnetic ground state from A-type AFM ordering of Co magnetic moment in CaCo2As2to FM ordering in Ca1-xPrxCo2As2(0.1 ⩽x⩽ 1). Most importantly, the abrupt drop of low temperature magnetic susceptibility belowTFiMwithx⩾ 0.25 and the observed magnetic pole reversal withx⩾ 0.4 suggests an AFM coupling between Co 3dand Pr 4fmagnetic sublattice. Finally, a detailed magnetic phase diagram in this system has been obtained.