Evolution of transition metal charge states in correlation with the structural and magnetic properties in disordered double perovskites Ca2−xLaxFeRuO6 (0.5 ≤ x ≤ 2)

• Published in: Physical chemistry chemical physics : PCCP Vol. 23; no. 38; pp. 21769 - 21783
• Main Authors: Kumari Naveen, Rom, Tanmay, Islam, Shams Sohel, Reehuis, Manfred, Adler, Peter, Felser, Claudia, Hoser, Andreas, Nath, Ramesh Chandra, Yadav, Ashok Kumar, Jha, Shambhu Nath, Bhattacharyya, Dibyendu, Schmidt, Marcus, Paul, Avijit Kumar
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 06.10.2021
• Subjects: Antiferromagnetism; Cations; Crystal defects; Crystal structure; Hypoxia; Magnetic permeability; Magnetic properties; Mossbauer spectroscopy; Neutron diffraction; Nonstoichiometric compounds; Oxidation; Perovskites; Ruthenium; Spectrum analysis; Thermogravimetric analysis; Transition metals; Transition temperature; Valence; X ray absorption
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d1cp02318g

A series of disordered Ca1.5La0.5FeRuO6, CaLaFeRuO6 and La2FeRuO6 double perovskites were prepared by the solid-state reaction method and investigated by neutron powder diffraction, X-ray absorption near-edge structure (XANES) analysis at the Ru–K edge, Mössbauer spectroscopy, DC magnetization and resistivity measurements. All compounds crystallize in the orthorhombic crystal structure with the space group Pbnm down to 3 K, showing a random distribution of Fe and Ru at the B site. Thermogravimetric analysis indicates oxygen deficiency in the Ca-rich and formal oxygen hyperstoichiometry in the La-rich members of the present series. While Mössbauer spectra verify the Fe3+ state for all compositions, the XANES study reveals a variable Run+ oxidation state which decreases with increasing La content. The end member actually is a Ru3+/Ru4+ compound with possibly some cation vacancies. From magnetic susceptibility and neutron diffraction measurements, the presence of a G-type antiferromagnetic ordering was observed with a drastic increase in transition temperature from 275 K (Ca1.5La0.5FeRuO6) to 570 K (La2FeRuO6). Mössbauer spectroscopy confirms the presence of long-range ordering but, due to local variations in the exchange interactions, the magnetic states are microscopically inhomogeneous. All the samples are variable range hopping semiconductors. A complex interplay between structural features, charge states, anion or cation defects, and atomic disorder determines the magnetic properties of the present disordered 3d/4d double perovskite series.