Jasper Arne Baldauf

The hydrogenation behavior of FeB type CeGe was investigated. Hydrogenation (deuteration) produces mixtures of two modifications, similar to hydrides of other FeB type phases LnTt (Ln = La, Ce, Nd; Tt = Si, Ge). P-CeGeD0.75(2) (Pnma, a = 8.1603(5) Å, b = 4.0938(3) Å, c = 6.2911(4) Å) crystallizes in the LaGeH structure type (filled FeB type), whereas C-CeGeD0.95(3) (Cmcm, a = 4.2958(2) Å, b = 11.9970(7) Å, c = 4.0885(3) Å) crystallizes in the ZrNiH structure type (filled CrB). Similar to CeSiHx the mixtures feature exceptionally high ferromagnetic ordering temperatures of 21.6(1) K for CeGeDx and 22.1(2) K for CeGeHx (x ≤ 1), with the effective magnetic moments of 2.44(1) μB (CeGeDx) and 2.38(1) μB (CeGeHx) being close to the free ion value of 2.54 μB of Ce3+. The hydrides (deuterides) were studied by neutron powder diffraction (NPD), thermal analysis and magnetic susceptibility measurements.

This investigation focuses on the solid-state synthesis and a detailed structural and phase analytical investigation of the CoxNi3–xGa4 series along a constant Ga compositional line within Co–Ni–Ga phase space. Combined analysis of single crystal X-ray diffraction and neutron powder diffraction of CoxNi3–xGa4, x = 1.5 reveals a random distribution of Co and Ni over a single Wyckoff site, which contrasts with previous report suggesting atomic ordering. Phase analyses via X-ray powder diffraction indicates a vacancy order–disorder transition as the Co concentration increases beyond a critical limit. DFT calculation predicted a semimetallic and nonmagnetic ground state, supported by the absence of magnetic peaks or intensity enhancement at 10 K neutron data compared to 300 K. Interestingly, Peierls-like distortions are observed within the Ga substructure in the vacancy-ordered phase, whereas such distortions are absent in the vacancy-disordered phase. These distortions result in periodic charge localization and exhibit subtle alterations between room temperature and 180 K. Magnetic measurements further reveal cluster spin-glass behavior with a high coercivity. The nontrivial spin dynamics, coupled with large coercivity, makes this phase a compelling candidate for multifunctional applications.

Two new hydrides, respectively deuterides, of the FeB-type CeSi were synthesized, and their reaction as well as magnetic behavior and structures were studied. Hydrogenation leads to two phases, a kinetic product retaining the FeB structure with hydrogen-filled tetrahedra (LaGeH type, Pnma, P-phase: CeSiD0.82(2)) and the thermodynamically preferred hydrogen-filled CrB-type structure (ZrNiH type, Cmcm, C-phase: CeSiD0.96(1)). Both hydrides are ferromagnets and feature Curie temperatures of 22.4(1) K (C-phase) and 24.3(1) K (P-phase), which are exceptionally high for cerium intermetallics. The effective magnetic moments of μ(Ce3+) = 2.53 μB are very close to the free ion value of 2.54 μB. The compounds were studied using in situ neutron powder diffraction and magnetic characterization and by density functional theory and chemical bonding analysis.

Synthesis of europium aluminates is usually conducted from the binary oxides (EuO/Eu2O3 + Al2O3) at high temperatures alongside a reductive gas for the stabilization of Eu2+. We are reporting on an alternative pathway starting from EuAl2 (cubic Laves phase, MgCu2 type, Fd3̅m), which was oxidized under different conditions. By heating the intermetallic precursor to different temperatures, first amorphous and at higher temperatures highly crystalline products were observed. However, the question of the Eu valence state in the product will immediately arise. Depending on the reaction procedure used both, the di- and trivalent state could be achieved in the reaction with elemental oxygen. EuIIIAlO3 (GdFeO3 type, Pnma) was observed as the sole crystalline product with excess O2 in the powder X-ray diffraction experiments. The differing chemical composition could be explained by the formation of amorphous γ-Al2O3 proven by 27Al solid-state NMR spectroscopy. Oxidizing EuAl2 under controlled conditions yields X-ray pure EuIIAl2O4 (SrAl2O4 type, P21). Surprisingly, annealing of the EuIIIAlO3/amorphous γ-Al2O3 mixture under vacuum led to the formation of EuIIAl2O4, which was investigated in detail. The different oxidation states of the Eu atoms were proven by magnetic measurements, 151Eu Mössbauer spectroscopic investigations, and photoluminescence studies.

This investigation focuses on the solid-state synthesis and a detailed structural and phase analytical investigation of the Co _???? Ni _3−???? Ga ₄ series along a constant Ga compositional line within Co⎼Ni⎼Ga phase space. Combined analysis of single crystal X-ray diffraction and neutron powder diffraction of Co _???? Ni _3−???? Ga ₄ , 𝑥 = 1.5 reveals a random distribution of Co and Ni over a single Wyckoff site, which contrasts with previous report suggesting atomic ordering. Phase analyses via X-ray powder diffraction indicates a vacancy order-disorder transition as the Co concentration increases beyond a critical limit. DFT calculation predicted a semi-metallic and nonmagnetic ground state, supported by the absence of magnetic peaks or intensity enhancement at 10 K neutron data compared to 300 K. Interestingly “Peierls-like” distortions are observed within the Ga substructure in the vacancy-ordered phase, whereas such distortions are absent in the vacancy-disordered phase. These distortions result in periodic charge localization and exhibit subtle alterations between room temperature and 180 K. Magnetic measurements further reveal cluster spin-glass behavior with a high coercivity. The non-trivial spin dynamics, coupled with large coercivity, makes this phase a compelling candidate for multifunctional applications.

This investigation focuses on the solid-state synthesis and a detailed structural and phase analytical investigation of the Co _???? Ni _3−???? Ga ₄ series along a constant Ga compositional line within Co⎼Ni⎼Ga phase space. Combined analysis of single crystal X-ray diffraction and neutron powder diffraction of Co _???? Ni _3−???? Ga ₄ , 𝑥 = 1.5 reveals a random distribution of Co and Ni over a single Wyckoff site, which contrasts with previous report suggesting atomic ordering. Phase analyses via X-ray powder diffraction indicates a vacancy order-disorder transition as the Co concentration increases beyond a critical limit. DFT calculation predicted a semi-metallic and nonmagnetic ground state, supported by the absence of magnetic peaks or intensity enhancement at 10 K neutron data compared to 300 K. Interestingly “Peierls-like” distortions are observed within the Ga substructure in the vacancy-ordered phase, whereas such distortions are absent in the vacancy-disordered phase. These distortions result in periodic charge localization and exhibit subtle alterations between room temperature and 180 K. Magnetic measurements further reveal cluster spin-glass behavior with a high coercivity. The non-trivial spin dynamics, coupled with large coercivity, makes this phase a compelling candidate for multifunctional applications.