Fe5–δGeTe2 was synthesized by heating the elements at 1050 K and characterized by single crystal and powder X‐ray analysis. The structure [R3m, a = 4.0376(4) Å, c = 29.194(6) Å] consists of Fe5–δGe layers separated by tellurium double layers forming a van der Waals gap. The pronounced two‐dimensional character of Fe5–δGeTe2 causes stacking faults along the c direction. Simulations of different stacking variants using the DIFFaX software reveal disorder occurring in domains. Magnetic measurements of Fe5–δGeTe2 show ferromagnetism below 279 K with a saturation moment of 1.80 μB at 1.8 K. Nickel substitution of the iron sites has little influence on the structure but changes the saturation moment, which passes through a maximum of 2.11 μB in Fe4.11Ni0.50GeTe2. This indicates that structural influences as well as the dilution of the magnetic iron atoms play a decisive role.

EuPtAl has been prepared from the elements via arc-melting and subsequent temperature treatment; the structure was refined from single crystal X-ray diffraction data. The compound crystallizes in an orthorhombic (3 + 1)D commensurately modulated structure (ScPtAl type) with space group Cmcm(α,0,0)0 s0 (α = 2/3). Full ordering of the Pt and Al atoms within the [PtAl] polyanion was observed. Magnetic measurements revealed an anomaly in the susceptibility data at T = 41.6(1) K, which was also observed as λ-type anomaly in heat capacity measurements ( T = 40.7(1) K). Temperature dependent powder X-ray diffraction experiments indicated a drastic shortening of the c axis (-18 pm, -1.1%) around 45 K, while the a axis nearly remains the same (-1 pm, -0.2%). Measurements of the electrical resistivity verified the anomaly, indicating a clear change in the electronic structure of the material. The observed anomalies in the physical measurements can be explained by a temperature driven first order valence change from Eu at higher temperatures (>55 K) to Eu at low temperatures. This valence change was proven by temperature dependent Eu Mössbauer spectroscopic investigations. Isostructural EuPtGa was prepared in comparison, and it shows divalent Eu atoms down to 2.5 K along with antiferromagnetic ordering at T = 13.1(1) K.

Dimensional reduction of superconducting anti PbO-type iron selenide has been achieved by terminating the tetragonal square layers of FeSe tetrahedra by ethylenediamine (en) ligands. We obtained three new structures in the Fe-Se-en system. FeSe(en) contains FeSe single chains bridged via Fe(en) complexes. FeSe(en) has FeSe double strands separated by Fe(en) complexes and free en molecules. FeSe(en) conserves the tetragonal layers of bulk FeSe which are now widely separated by en molecules. Through systematic dilution of the solvent we were able to introduce an additional parameter in solvothermal synthesis and thus have control over the connectivity of the tetrahedra. Additionally, a phase diagram of the Fe-Se-en system is generated by variation of the reaction temperature. The magnetic properties of the FeSe derivatives range from superconductivity and antiferromagnetism to paramagnetism.

We report muon spin rotation (µSR) and magnetization measurements under pressure on Fe 1+δ Se1-xSx with x ≈ 0.11. We find an extended dome of long range magnetic order above p ≈ 0.6 GPa spanning a pressure range between previously reported separated magnetic phases. The magnetism initially competes with coexisting superconductivity leading to a local maximum and minimum of the superconducting Tc(p). The maximum of Tc corresponds to the onset of magnetism while the minimum coincides with the pressure of strongest competition. A shift of the maximum of Tc(p) for a series of single crystals with x up to 0.14 roughly extrapolates to a putative magnetic and superconducting state at ambient pressure for x ≥ 0.2.

A temperature induced valence phase transition from Yb3+ at higher temperatures to Yb2+ at lower temperatures was observed at T = 110(1) K for intermetallic YbPd2Al3.