Low-temperature properties of magnetically frustrated rare-earth zirconates A ₂Zr₂O₇

Abstract

Rare-earth A 2Zr2O7 zirconates have attracted considerable attention of the scientific community for their complex magnetic, electronic and material properties applicable in modern technologies. Light rare-earth members of the series, crystallising in the so-called pyrochlore variant of cubic crystal structure, have been studied in detail. HeavierA 2Zr2O7 compounds have been investigated mainly from the material properties viewpoint, focussing on their thermal properties and stability at high temperature and pressure. Low-temperature studies were mostly missing until recently. We present the low-temperature magnetic and thermodynamic properties of A 2Zr2O7 with A = Y, La, Nd, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu, well covering the whole series,the heavy rare-earth zirconates newly synthesised by high-temperature sintering and melting methods. X-ray diffraction reveals/confirms the ordered pyrochlore structure in light members, the disordered cubic structure of the defect-fluorite type in A 2Zr2O7 with A = Y, Gd – Yb, and the lower symmetry rhombohedral structure in the end-member Lu2Zr2O7. The specific heat of investigated compounds is dominated by the low-temperature anomaly associated with the magnetic ordering, long-range in light rare-earth zirconates, and short-range in heavier members. Effective magnetic moment in studied compounds, determined by fitting the magnetisation data to the Curie-Weiss formula, is in good agreement with the value of the A 3+ free ion. The magnetic properties were documented to be strongly influenced by the frustration of magnetic moments, connected to atomic disorder on the geometrically frustrated lattice. The experimental results are discussed in the framework of previous studies on A 2Zr2O7 zirconates, as well as other A 2 B 2O7 compounds.