Evolution of the magnetic order of Fe and Eu sublattices in Eu1−x Ca x Fe2As2 (0 ≤ x ≤ 1) single crystals

Abstract

Single crystals of Eu1−x Ca x Fe2As2 () are grown using the high-temperature solution-growth method employing FeAs self-flux. Structural and chemical analysis indicates that these crystals are homogeneous and their lattice parameters exhibit a gradual monotonic decrease with increasing Ca concentration. Detailed magnetic, specific heat and resistivity data were used to construct a phase diagram which depicts the evolution of the structural/spin-density-wave transition at T 0, and of the antiferromagnetic (AFM) ordering temperature of the Eu moments at T N. We found out that while T N decreases monotonically from 19.1 K (for x = 0) to below 2 K (for ), T 0 remains almost constant up to x = x c and decreases steadily for higher values of x. Annealing at low temperatures for several days leads to enhancement of T N and T 0 by a few kelvin and sharpened the anomalies associated with these transitions. However, annealing did not change the variation of T N and T 0 across the series. The observation that T 0 is almost constant until the long-range AFM ordering of the Eu2+ moments gets destroyed, suggests a subtle interrelationship between the Eu2+ and Fe2+ magnetic sublattices.