The physical properties and the band structure of the layered pnictide SrMnBi 2 were investigated. This compound has a crystal structure similar to that of the superconducting Fe pnictides, and is a bad metal with large residual resistivity. Magnetic order sets in at very high temperatures, around 290 K, as shown by magnetization, resistivity, and specific heat data. Band structure calculations using density functional theory (DFT) are consistent with the thermodynamic and transport measurements, suggesting a checkerboard antiferromagnetic (cAFM) ground state and a localized picture for the magnetism. Moreover, DFT results indicate that the Mn 3d electrons are strongly correlated, and that, unlike in the known superconductors, the Sr-Bi (1) layer is metallic. One more notable feature of the DFT calculation is the multiple Dirac-cone-like dispersion close to the Fermi level.
It is generally believed that fractional quantum excitations such as spinons in one-dimensional (1D) spin chains only proliferate and govern magnetism in systems with small and isotropic atomic magnetic moments, such as spin−1/2 Cu 2+ . In contrast, large and anisotropic orbital-dominated moments, such as those produced by strong spin-orbit coupling in the rare earths, are considered to be classical, becoming static as T → 0 since the conventional Heisenberg-Dirac exchange interaction [1, 2] cannot reverse their directions. We present here the results of neutron scattering measurements on Yb 2 Pt 2 Pb that completely negate this common wisdom. A diffuse continuum of magnetic excitations is observed in Yb 2 Pt 2 Pb, direct evidence that the elementary excitations carry a fractional spin quantum number, S = 1/2. The excitations disperse in only one direction, showing that the Yb moments form spin chains that are embedded in, but effectively decoupled from the three-dimensional conduction electron bands in metallic Yb 2 Pt 2 Pb. The spectrum of magnetic excitations strongly resembles the spinon continuum found in S = 1/2 Heisenberg spin chains, and indeed comparison to the 1D XXZ Hamiltonian indicates only a moderate exchange anisotropy, ∆ = J zz /J xx ∼ 3. Here we show how the orbital physics of 4f -electron exchange interactions can reconcile this moderately-anisotropic quantum Hamiltonian with the extreme anisotropy of the putatively classical Yb (J = 7/2) magnetic moments with respect to magnetic fields. We find that the unexpected quantum behavior emerges at low energies from the competition of interactions that act on much higher energy scales, i.e. the strong on-site Coulomb and spin-orbit interactions, as well as the crystal fields, and the inter-site hopping. Our findings thus provide a unique and a hitherto unforeseen manifestation of emergence [3] of quantum physics in the system of semi-classical electronic orbitals.The unusual properties of Yb 2 Pt 2 Pb derive in part from its crystal structure (Fig. 1A,B), where the Yb 3+ ions form ladders along the c−axis, with rungs on the orthogonal bonds of the ShastrySutherland Lattice (SSL) [5] in the ab-planes. Equally important is the strong spin-orbit coupling, which combines spin and orbital degrees of freedom into a large, J = 7/2 Yb moment.The absence of a Kondo effect indicates minimal coupling of Yb to the conduction electrons of this excellent metal [6, 7]. A point-charge model (Supplementary Information) indicates that the crystal electric field (CEF) lifts the eightfold degeneracy of the Yb 3+ moments, producing a Kramers doublet ground state that is a nearly pure state of the total angular momentum, J , |J, m J = |7/2, ±7/2 . The estimated anisotropy of the Landé g-factor is in good agreement with that of the measured magnetization, g /g ⊥ = 7.5(4) [6][7][8], implying strong Ising anisotropy in Yb 2 Pt 2 Pb, which confines the individual Yb moments to two orthogonal sublattices in the The reality is, in fact, completely different.The neutron scatt...
We present an experimental study of the effects of oxidation on the magnetic and crystal structures of exchange biased epsilon-Co/CoO core-shell nanoparticles. Transmission electron microscopy measurements reveal that oxidation creates a Co-CoO interface which is highly directional and epitaxial in quality. Neutron diffraction measurements find that below a Néel temperature TN of approximately 235 K the magnetization of the CoO shell is modulated by two wave vectors, q1=(1/2 1/2 1/2)2pi/a and q2=(100)2pi/a. Oxidation affects the q1 component of the magnetization very little, but hugely enhances the q2 component, resulting in the magnetic decompensation of the core-shell interface. We propose that the large exchange bias effect results from the highly ordered interface between the Co core and CoO shell, and from enhanced core-shell coupling by the uncompensated interface moment.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.