Ferrimagnetic cluster formation due to oxygen vacancies in CaFe2 O4-δ
Journal
Physical Review B
Journal Volume
98
Journal Issue
14
Pages
144404-1 - 144404-10
Date Issued
2018
Author(s)
Abstract
CaFe2O4 possesses an intriguing crystal structure characterized by the presence of FeO6 octahedra that share both edges and corners, and featuring zigzag Fe chains that are assembled in a honeycomb tube network. The nominal CaFe2O4 has been identified to show a long-range antiferromagnetic spin ordering of Néel temperature TN∼184 K. From dc and ac magnetic susceptibility measurements on both polycrystalline and single-crystal samples, a random distribution of ferrimagnetically ordered clusters of Fe spins is proposed to exist in the oxygen deficient CaFe2O4-δ. The ferrimagnetic ordering is proposed, coming from the oxygen vacancy-induced Fe3+ to Fe2+ conversion for the antiferromagnetically coupled spins of Fe2+ ions in the low-spin state and the Fe3+ ions in the high-spin state, which leads to an incomplete cancellation of staggered magnetization below TN. Current model reasonably explains the inconsistencies found in the literature regarding the persistent ferromagnetic component for CaFe2O4, having a confirmed antiferromagnetic long-range spin ordering from neutron diffraction studies. We calculate the antiferromagnetic spin structure and the parameters of a Heisenberg Hamiltonian via spin-polarized density functional theory, obtaining results that are consistent, to a very high degree, with our experimental results for ac and dc magnetic susceptibility.
Publisher
American Physical Society
Type
journal article