Crystal and Magnetic Structures of the Chain Antiferromagnet CaFe₄Al₈

Abstract

The crystal structure of CaFeAl was studied by X-ray single crystal and powder diffraction as well as high-resolution neutron powder diffraction. CaFeAl crystallizes with a tetragonal CeMnAl-type structure, an ordered variant of the ThMn-type (Pearson symbol tI26, space group I4/ mmm, a = 8.777(1), c = 5.077(1) Å). Similarly to the well-known A15-type superconductors, the structure of CaFeAl contains one-dimensional chains of d-metal atoms, which are parallel to the crystallographic fourfold axis. CaFeAl is paramagnetic at room temperature and exhibits long-range antiferromagnetic ordering at about 180 K, combined with a short-range ordered spin arrangement. The magnetic structure, determined by powder neutron diffraction at 4 K, shows that the magnetic moments on the Fe atoms form mirror-inverted chains along the c-direction and are slightly canted from the axis.

Electronic structure of YbFe$_4$Al$_8$ antiferromagnet: A combined X-ray photoelectron spectroscopy and first-principles study

“…Earlier Although it is confirmed that there are two magnetic Fe sublattices in the YbFe 4 Al 8 , the exact type of antiferromagnetic configuration is not known. The powder neutron diffraction at 4 K for the isostructural compound CaFe 4 Al 8 has shown that the magnetic moments on the Fe atoms form antiparallel chains oriented along the cdirection and slightly canted from the axis [69], which can be described as a canted AFM-C configuration. Since the FPLO code only allows the calculation of collinear magnetic configurations, we consider for the YbFe 4 Al 8 simplified collinear AFM-C model.…”

“…As the initial lattice parameters, we take the values 8.714 and 5.026 Å measured for YbFe 4 Al 8 [2]. Since the literature does not provide atomic positions for the studied compound, we take ini-tial positions from the isostructural CaFe 4 Al 8 (neutron powder data, T = 4 K) [69]. As a result of optimizing the lattice parameters and atomic positions, we obtain the AFM-C structure presented in Table I.…”