Magnetic and Structural Phase Transitions of EuFe₂As₂ Studied via Neutron and Resonant X-ray Scattering

Magnetic and superconducting anisotropy in Ni-doped RbEuFe4As4 single crystals

“…Even for the largest Ni concentrations investigated here, the Eu moments order below the superconducting transition. Consistent with the resistivity data, there is no additional feature in the specific heat between 2 K and room temperature that would indicate a spin-density wave (on the Fe site) as is seen in most 122 parent compounds [3][4][5][6][7][8][9]22,25,39 . Figure 5 shows the superconducting contribution to the specific heat of the four samples obtained by subtracting a linear extrapolation of the normal state data above T c .…”

“…Recently, it has been realized 20 that the high purity and symmetry properties of 1144 materials such as CaKFe 4 As 4 may open a new platform for the observation of topological bandstructures and Majorana zero modes. The AEuFe 4 As 4 compounds represent a peculiar subgroup of this new family as the planes of Eu 2+ ions can order magnetically as has been shown previously in EuFe 2 As 2 [21][22][23][24][25] . Initial experiments on polycrystalline RbEuFe 4 As 4 samples indicate ferromagnetic in-plane ordering at 15K deep within the superconducting phase (T c = 37 K) 17,18 .…”

Thermal properties and Ising critical behavior in EuFe 2 As 2

“…In the case of EuFe 2 As 2 , a spin arrangement on the basal plane ab must correspond to the 3D-XY universality class (as it happens, for instance, in the case of CsMnF 3 and SmMnO 3 [14]) while a clear anisotropy due to the alignment along a particular direction in that plane will correspond to the 3D-Ising universality class such as, for instance, FeF 2 [15]. In the only work in which attention has been paid to the study of the critical behavior of this transition, the conclusion was that it belongs to the Heisenberg class, in clear contradiction with the observed anisotropy of the spins arrangement [16]; the evaluated critical behavior was that associated with the magnetic parameters.…”

Ultrafast Momentum-Dependent Response of Electrons in AntiferromagneticEuFe2As2Driven by Optical Excitation

“…In undoped and weakly doped compounds, the strong nesting of hole and electron Fermi surfaces along q SDW ¼ ð; Þ leads at low temperatures to AFM ordering of Fe magnetic moments and the formation of a spin density wave (SDW), which is accompanied or preceded by a structural transition from tetragonal to orthorhombic structure [10,11]. Experiments demonstrated strong coupling between magnetic and structural transitions [12,13] and Ising nematic order is considered to induce orbital anisotropy [14,15]. Below the Néel transition temperature T N , this magnetic ordering leads to backfolding of electron bands to À, where they hybridize with the hole bands and modify the FS near À by a SDW energy gap, see Fig.…”