Magnetic phase diagram of Ca-substituted EuFe2As2

Abstract

The simultaneous presence of a Fe-related spin-density wave and antiferromagnetic order of Eu 2+ moments ranks EuFe 2 As 2 among the most interesting parent compounds of iron-based pnictide superconductors. Here we explore the consequences of the dilution of Eu 2+ magnetic lattice through on-site Ca substitution. By employing macro-and microscopic techniques, including electrical transport and magnetometry, as well as muon-spin spectroscopy, we study the evolution of Eu magnetic order in both the weak and strong dilution regimes, achieved for Ca concentration x(Ca) = 0.12 and 0.43, respectively. We demonstrate the localized character of the Eu antiferromagnetism mediated via RKKY interactions, in contrast with the largely itinerant nature of Fe magnetic interactions. Our results suggest a weak coupling between the Fe and Eu magnetic sublattices and a rapid decrease of the Eu magnetic interaction strength upon Ca substitution. The latter is confirmed both by the depression of the ordering temperature of the Eu 2+ moments, T N , and the decrease of magnetic volume fraction with increasing x(Ca). We establish that, similarly to the EuFe 2 As 2 parent compound, the investigated Ca-doped compounds have a twinned structure and undergo a permanent detwinning upon applying an external magnetic field. arXiv:1805.03896v2 [cond-mat.mtrl-sci]

Spin order and fluctuations in the EuAl4 and EuGa4 topological antiferromagnets: A μSR study

“…Such enhanced local-field distribution might be related to the complex spatial arrangement of the Eu magnetic moments in EuAl 4 , where the magnetic propagation vector is incommensurate with the crystal lattice [31]. By contrast, in EuGa 4 , λ T (T ) follows the typical behavior of materials with a long-range (anti)ferromagnetic order [36], i.e., diverging at T N and continuously decreasing at T < T N . Such λ T (T ) suggests a very homogeneous distribution of local fields, consistent with the commensurate magnetic propagation vector in EuGa 4 [32].…”

“…( 1). Similar expressions have been used to analyze the μSR data in other Eu-based magnetic materials, most notably, in the Eu122 iron pnictides [36,37].…”

Electronic structure and H−T phase diagram of Eu(Fe1−xRhx)<

“…4(g) and 4(i) for low fields along the c and a axes, respectively. In most doped EuFe 2 As 2 materials, particularly in in-plane fields 10,11,[20][21][22] , the material does not exhibit full diamagnetism in the superconducting state, only a diamagnetic shift on top of a large paramagnetic background. In general, a field-trained difference can be explained by either the freezing-in of magnetic moments or by superconductivity with vortex pinning.…”

“…The rapid shift to lower temperature is inconsistent with the very gradual field dependence of the resistive superconducting transition 9 , suggesting an antiferromagnetic origin, but we note that resistive measurements may not be bulk-sensitive if superconductivity is present. In nonsuperconducting Cadoped (Eu 0.88 Ca 0.12 )Fe 2 As 2 , an antiferromagnetic transition observed in the susceptibility at 15 K is suppressed to zero by a 1.5 T field applied along the c axis, or by a 0.75 T in-plane field 20 . The suppression of the specific heat jump in Fig.…”

“…In magnetic field, the Ca-doped material 20 and highpressure-synthesized EuFe 2 As 2 21 exhibit a transition from the paramagnetic normal state to field-induced ferromagnetic order, which moves rapidly to higher temperature as field is applied. The broad specific heat hump that grows out of the sharp phase transition in Eu(Fe 0.88 Rh 0.12 ) 2 As 2 has a similar field dependence.…”