Spin polarized density functional theory calculations of the electronic structure and magnetism of the 112 type iron pnictide compound $$\hbox {EuFeAs}_2$$

Using density-functional theory, we investigate the electronic, magnetic, and hyperfine-interaction properties of the 112-type iron-pnictide compound $${\hbox {EuFeAs}}_2$$ EuFeAs 2 , which is isostructural to the high-temperature iron-based superconductor $${\hbox {Ca}}_{1-x}{\hbox {La}}_x{\hbox {FeAs}}_2$$ Ca 1 - x La x FeAs 2 . We show that the band structure of $${\hbox {EuFeAs}}_2$$ EuFeAs 2 is similar to that of the 112-type compounds’ family, with hole-like and electron-like bands at the Brillouin-zone center and corners, respectively. We demonstrate that the bands near the Fermi level originate mainly from the Fe atoms. The presence of a mixture of ionic and covalent bonding is predicted from the charge-density and atom-resolved density-of-states calculations. There is good agreement between the calculated hyperfine-interaction parameters with those obtained from the $$^{57}$$ 57 Fe and $$^{151}$$ 151 Eu Mössbauer measurements. The spatial distribution of atoms in $${\hbox {EuFeAs}}_2$$ EuFeAs 2 leads to an in-plane 2D magnetism. Moreover, ab-initio calculations predict the compound’s magnetic moment and the magnetic moments of each constituent atom. Also, the density of states profile provides insight into the relative magnitude of these moments. Electronic structure calculations and Fermi surface topology reveal various physical and chemical properties of $${\hbox {EuFeAs}}_2$$ EuFeAs 2 . Valence electron density maps indicate the co-existence of a wide range of chemical bonds in this system, and based on structural properties, the transport characteristics are deduced and discussed. A thorough analysis of the atomic structure of $${\hbox {EuFeAs}}_2$$ EuFeAs 2 and its role in the bond formation is presented.

Clock Transition Due to a Record 1240 G Hyperfine Interaction in a Lu(II) Molecular Spin Qubit

Spins in molecules are particularly attractive targets for next-generation quantum technologies, enabling chemically programmable qubits and potential for scale-up via self-assembly. Here, we demonstrate chemical control of the degree of s-orbital mixing into the spin-bearing d-orbital associated with a series of spin-½ La(II) and Lu(II) molecules. Increased s-orbital character reduces spin-orbit coupling and enhances the electron-nuclear Fermi contact interaction. Both outcomes are beneficial for quantum applications: the former reduces spin-lattice relaxation, while the latter gives rise to a record molecular hyperfine interaction for Lu(II) that, in turn, generates a massive 9 GHz hyperfine clock transition and an order of magnitude increase in phase memory time. These findings suggest new strategies for development of molecular quantum technologies, akin to trapped ion systems.