Crucial Role of Site Disorder and Frustration in Unusual Magnetic Properties of Quasi-2D Triangular Lattice Antimonate Na4FeSbO6

• Published in: Applied magnetic resonance 2015-10, Vol.46 (10), p.1121-1145
• Main Authors: Zvereva, Elena A., Presniakov, Igor A., Whangbo, Myung-Hwan, Koo, Hyun-Joo, Frantsuzenko, Tatyana V., Savelieva, Olga A., Sobolev, Alexey V., Nalbandyan, Vladimir B., Shih, Pei-Shan, Chiang, Jen-Che, Lee, Jenn-Min, Chen, Jin-Ming, Lin, Jiunn-Yuan, Büchner, Bernd, Vasiliev, Alexander N.
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Atoms and Molecules in Strong Fields; Crystal structure; Curie temperature; Electron paramagnetic resonance; Electron spin; Electrons; Ferric ions; Iron; Laser Matter Interaction; Magnetic fields; Magnetic permeability; Magnetic properties; Organic Chemistry; Physical Chemistry; Physics; Physics and Astronomy; Radiation; Solid State Physics; Spectroscopy/Spectrometry; Spectrum analysis; Spin resonance; Subsystems; X ray absorption
• ISSN: 0937-9347; 1613-7507
• DOI: 10.1007/s00723-015-0700-5

The effect of antisite disorder in the layered sodium iron antimonate Na 4 FeSbO 6 was examined both experimentally and theoretically. The magnetic susceptibility and specific heat measurements show that Na 4 FeSbO 6 does not undergo a long-range antiferromagnetic order, unlike its structural analog Li 4 FeSbO 6 . The electron spin resonance yields the complicated picture of coexistence of two magnetic subsystems corresponding to two different Fe cation positions in the lattice (regular and antisite) and driving the magnetic properties of the Na 4 FeSbO 6 . This conclusion found perfect confirmation from both the Mössbauer and X-ray absorption data which show the presence of two kinds of Fe 3+ ions being in high-spin Fe 3+ ( S  = 5/2) and low-spin Fe 3+ ( S  = 1/2) states. These findings arise from the antisite disorder between the Fe 3+ and Sb 5+ ions in the (NaFeSbO 6 ) 3− layers of Na 4 FeSbO 6 . Our density functional calculations show that the Fe 3+ ions located at the Sb 5+ sites exist as low-spin Fe 3+ ions, and that the spins of each Fe 3+ ( S  = 5/2)–Fe 3+ ( S  = 1/2)–Fe 3+ ( S  = 5/2) trimer generated by the antisite disorder has a ferrimagnetic arrangement Fe 3+ ↑–Fe 3+ ↓–Fe 3+ ↑, which enhances the magnetization of Na 4 FeSbO 6 and leads to an apparently positive Curie–Weiss temperature.