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

Abstract

Single crystals of Eu Ca FeAs ([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 , and of the antiferromagnetic (AFM) ordering temperature of the Eu moments at T. We found out that while T decreases monotonically from 19.1 K (for x = 0) to below 2 K (for [Formula: see text]), T remains almost constant up to x = x and decreases steadily for higher values of x. Annealing at low temperatures for several days leads to enhancement of T and T by a few kelvin and sharpened the anomalies associated with these transitions. However, annealing did not change the variation of T and T across the series. The observation that T is almost constant until the long-range AFM ordering of the Eu moments gets destroyed, suggests a subtle interrelationship between the Eu and Fe magnetic sublattices.

Evolution of magnetic properties in iron-based superconductor Eu-doped CaFe2As2

“…From the C value obtained, we have estimated the effective magnetic moment of Eu 2+ , μ eff = (7.97 ± 0.10) μ B . These values are comparable with those previously reported (Jiang et al, 2009;Harnagea et al, 2018;Tran et al, 2018) for a similar Eu-doping level. The positive θ value implies ferromagnetic (FM) interaction between Eu 2+ moments.…”

“…Frontiers in Electronic Materials frontiersin.org Eu 2+ moments. As shown in the insets to Figures 3A-C, there is a tiny but distinguishable anomaly at T SDW ~165-185 K. These T SDW values are in close agreement with those previously reported based on resistivity and magnetization measurements (Jiang et al, 2009;Harnagea et al, 2018;Tran et al, 2018;Shrestha et al, 2020). We subsequently determined T SDW for various ECFA samples and plotted it as a function of Eu doping.…”

“…At x = 1, θ = (19.71 ± 0.19). This θ value is comparable with those of 20.3 K reported by Harnagea et al (2018) and 19.7 K reported by Jiang et al (2009). Similarly, the Eu-doping-dependent best fit of C is shown in Figure 4B and has nearly linear dependence on x.…”

“…Therefore, we have followed the same approach and calculated Δχ (T) by subtracting the CW contribution of the (Shrestha et al, 2020). and (Harnagea et al, 2018), respectively. T SDW increases rapidly with increasing x and then slowly saturates to T SDW ~190 K above x ~0.4.…”

Spin reorientation of the Fe moments in Eu0.5Ca0.5Fe2As2 : Evidence for strong interplay of Eu and Fe magnetism

“…On the other hand, dilution of the Eu sublattice with nonmagnetic Ca 2+ ions suppresses its AFM ordering temperature (T Eu ) gradually. [38][39][40] A arXiv:1904.01086v1 [cond-mat.str-el] 1 Apr 2019 recent µSR study on Eu 0.5 Ca 0.5 Fe 2 As 2 suggests a long-range magnetically ordered Eu sublattice. 39 However, it was proposed based on macroscopic measurements that substitution of 50 % Eu ions might lead to a short-range ordered nature of Eu magnetism.…”