Portal de Periódicos da CAPES

Ferrimagnetic cluster formation due to oxygen vacancies in CaFe 2 O 4 − δ

2018; American Physical Society; Volume: 98; Issue: 14 Linguagem: Inglês

10.1103/physrevb.98.144404

2469-9977

Rajasree Das, Saikat Debnath, G. Narsinga Rao, Shobhana Narasimhan, F. C. Chou,

Multiferroics and related materials

${\mathrm{CaFe}}_{2}{\mathrm{O}}_{4}$ possesses an intriguing crystal structure characterized by the presence of ${\mathrm{FeO}}_{6}$ octahedra that share both edges and corners, and featuring zigzag Fe chains that are assembled in a honeycomb tube network. The nominal ${\mathrm{CaFe}}_{2}{\mathrm{O}}_{4}$ has been identified to show a long-range antiferromagnetic spin ordering of N\'eel temperature ${T}_{N}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}184$ 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 ${\mathrm{CaFe}}_{2}{\mathrm{O}}_{4\ensuremath{-}\ensuremath{\delta}}$. The ferrimagnetic ordering is proposed, coming from the oxygen vacancy-induced ${\mathrm{Fe}}^{3+}$ to ${\mathrm{Fe}}^{2+}$ conversion for the antiferromagnetically coupled spins of ${\mathrm{Fe}}^{2+}$ ions in the low-spin state and the ${\mathrm{Fe}}^{3+}$ ions in the high-spin state, which leads to an incomplete cancellation of staggered magnetization below ${T}_{N}$. Current model reasonably explains the inconsistencies found in the literature regarding the persistent ferromagnetic component for ${\mathrm{CaFe}}_{2}{\mathrm{O}}_{4}$, 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.