Evolution of the magnetic order of Fe and Eu sublattices in Eu_1-x Ca _x Fe₂As₂ (0 ⩽ x ⩽ 1) single crystals

Single crystals of Eu_1-x Ca _x Fe₂As₂ ([Formula: see text]) 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 [Formula: see text]), 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.