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1. Magnetism and fermiology of kagome magnet YMn6Sn4Ge2

   https://doi.org/10.1038/s41535-023-00616-0  

   Bhandari, Hari; Dally, Rebecca L; Siegfried, Peter E; Regmi, Resham B; Rule, Kirrily C; Chi, Songxue; Lynn, Jeffrey W; Mazin, I I; Ghimire, Nirmal J (December 2024, npj Quantum Materials)

   Abstract Kagome lattice magnets are an interesting class of materials as they can host topological properties in their magnetic and electronic structures. YMn₆Sn₆is one such compound in which various exotic magnetic and electronic topological properties have been realized. Here, by means of a partial substitution of Sn with an isovalent and slightly smaller atom Ge, we demonstrate the sensitivity of such chemical substitution on the magnetic structure and its influence in the electronic properties. Magnetic structure of YMn₆Sn₄Ge₂determined by neutron diffraction reveals an incommensurate staggered magnetic spiral with a slightly larger spiral pitch than in YMn₆Sn₆. This change in magnetic structure influences the Fermi surface enhancing the out-of-plane conductivity. Such a sensitivity to the partial chemical substitution provides a great potential for engineering the magnetic phases and associated electronic properties not only in YMn₆Sn₆, but also in the large family of 166 rare-earth kagome magnet. 

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2. Synthesis, Elasticity, and Spin State of an Intermediate MgSiO ₃ ‐FeAlO ₃ Bridgmanite: Implications for Iron in Earth's Lower Mantle

   https://doi.org/10.1029/2020JB019964  

   Zhu, Feng; Liu, Jiachao; Lai, Xiaojing; Xiao, Yuming; Prakapenka, Vitali; Bi, Wenli; Alp, E. Ercan; Dera, Przemyslaw; Chen, Bin; Li, Jie (July 2020, Journal of Geophysical Research: Solid Earth)

   Abstract Fe‐Al‐bearing bridgmanite may be the dominant host for ferric iron in Earth's lower mantle. Here we report the synthesis of (Mg_0.5Fe³⁺_0.5)(Al_0.5Si_0.5)O₃bridgmanite (FA50) with the highest Fe³⁺‐Al³⁺coupled substitution known to date. X‐ray diffraction measurements showed that at ambient conditions, the FA50 adopted the LiNbO₃structure. Upon compression at room temperature to 18 GPa, it transformed back into the bridgmanite structure, which remained stable up to 102 GPa and 2,600 K. Fitting Birch‐Murnaghan equation of state of FA50 bridgmanite yieldsV₀ = 172.1(4) ų,K₀ = 229(4) GPa withK₀′ = 4(fixed). The calculated bulk sound velocity of the FA50 bridgmanite is ~7.7% lower than MgSiO₃bridgmanite, mainly because the presence of ferric iron increases the unit‐cell mass by 15.5%. This difference likely represents the upper limit of sound velocity anomaly introduced by Fe³⁺‐Al³⁺substitution. X‐ray emission and synchrotron Mössbauer spectroscopy measurements showed that after laser annealing, ~6% of Fe³⁺cations exchanged with Al³⁺and underwent the high‐ to low‐spin transition at 59 GPa. The low‐spin proportion of Fe³⁺increased gradually with pressure and reached 17–31% at 80 GPa. Since the cation exchange and spin transition in this Fe³⁺‐Al³⁺‐enriched bridgmanite do not cause resolvable unit‐cell volume reduction, and the increase of low‐spin Fe³⁺fraction with pressure occurs gradually, the spin transition would not produce a distinct seismic signature in the lower mantle. However, it may influence iron partitioning and isotopic fractionation, thus introducing chemical heterogeneity in the lower mantle. 

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3. Band structure engineering of chemically tunable LnSbTe (Ln = La, Ce, Pr)

   https://doi.org/10.1063/1.5123396  

   Weiland, Ashley; Chaparro, David_G; Vergniory, Maia_G; Derunova, Elena; Yoon, Jiho; Oswald, Iain_W_H; McCandless, Gregory_T; Ali, Mazhar; Chan, Julia_Y (October 2019, APL Materials)

   The ZrSiS family of compounds has garnered interest as Dirac nodal-line semimetals and offers an approach to study structural motifs coupled with electronic features, such as Dirac crossings. CeSbTe, of the ZrSiS/PbFCl structure type, is of interest due to its magnetically tunable topological states. The crystal structure consists of rare earth capped square nets separating the magnetic Ce–Te layers. In this work, we report the single crystal growth, magnetic properties, and electronic structures of LnSb1−xBixTe (Ln = La, Ce, Pr; x ∼ 0.2) and CeBiTe, adopting the CeSbTe crystal structure, and the implication of tuning the electronic properties by chemical substitution. 

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4. High pressure neutron diffraction study of magnetic ordering in erbium

   https://doi.org/10.1016/j.jmmm.2024.172066  

   Clay, Matthew P.; Sereika, Raimundas; Higgins, Maurissa K.; dos Santos, Antonio M.; Molaison, Jamie J.; Vohra, Yogesh K. (May 2024, Journal of Magnetism and Magnetic Materials)

   We have studied magnetic ordering in polycrystalline erbium at high pressures up to 32 GPa and low temperatures down to 10 K using neutron diffraction techniques at the Spallation Neutron Source at Oak Ridge National Laboratory, USA. For the hexagonal close-packed (hcp) phase, strong nuclear and magnetic satellite intensities permit a simultaneous refinement of the nuclear and magnetic structures. At 1 GPa of applied pressure, a modulation vector q=γc^* with γ≈2/7 for the c-axis modulated and cycloidal phases is consistent with prior single-crystal studies at low pressures. At 6.7 GPa in the hcp phase, we find γ≈0.31, indicating a reduction in the period of the magnetic structure with respect to the crystal lattice. The magnetic ordering temperature at 6.7 GPa is slightly above 60 K. At 32 GPa in the double hexagonal close-packed phase, the magnetic scattering constrains the magnetic ordering temperature to 25±5 K. Our neutron diffraction study demonstrates that the magnetic ordering persists in the high-pressure double hexagonal close-packed phase of erbium to the highest pressure of 32 GPa. 

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5. Theoretical and Experimental Insights Into Effects of Zn doping on Magnetic and Magnetocaloric Properties of MnCoGe

   https://doi.org/10.1021/acs.chemmater.0c02294  

   Wang, YiXu; Yannello, Vincent; Graterol, Jacnel; Zhang, Hu; Long, Yi; Shatruk, Michael (July 2020, Chemistry of Materials)

   MnCoGe-based materials have the potential to exhibit giant magnetocaloric effects due to coupling between magnetic ordering and a martensitic phase transition. Such coupling can be realized by matching the temperatures of the magnetic and structural phase transitions. To understand the site preference of different elements and the effect of hole or electron doping on the stability of different polymorphs of MnCoGe, crystal orbital Hamilton population (COHP) analysis has been employed for the first time to evaluate peculiarities of chemical bonding in this material. The shortest Mn–Mn bond in the structure is found to be pivotal to the observed ferromagnetic behavior and structural stability of hexagonal MnCoGe. Based on this insight, eliminating anti-bonding features of the shortest Mn-Mn bond at the Fermi energy is proposed as a feasible way to stabilize the hexagonal polymorph, which is then realized experimentally by substitution of Zn for Ge. The hexagonal MnCoGe structure is stabilized due to depopulation of the anti-bonding states and strengthening of the Mn–Mn bonding. This change in chemical bonding leads to anisotropic evolution of lattice parameters. The structural and magnetic properties of Zn-doped MnCoGe have been elucidated by synchrotron X-ray diffraction and magnetic measurements, respectively. 

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