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1. Ferrimagnetism and half-metallicity in Cr-substituted Mn _4–x Cr _x Al ₁₁

   https://doi.org/10.1088/1361-648X/add8d8  

   Noor, M_F B; Law, K-M; Yasmin, N; Hauser, A J; Besara, T (May 2025, Journal of Physics: Condensed Matter)

   Abstract Single crystals of disordered Mn_4–xCr_xAl₁₁have been synthesized via the flux method. EDS on several crystals of various sizes and shapes revealed an average molar ratio of 17:9:74 for Mn:Cr:Al, while x-ray diffraction on three different crystals yield compositions Mn_2.26Cr_1.74Al₁₁(Mn_4–xCr_xAl₁₁,x= 1.74), Mn_0.83Cr_3.17Al₁₁, and Mn_1.07Cr_2.93Al₁₁. This compound crystallizes in space group $P\overline{1}$, isostructural with both Mn₄Al₁₁and Cr₄Al₁₁. Magnetic measurements on several crystals show that this disordered compound is ferrimagnetic with a low effective moment of ${\mu }_{\text{eff}}\approx 1.012\pm 0.004{\mu }_{\text{B}}/\text{f}.\text{u}.$and a non-reachable transition temperature. Density functional theory calculations display opening of a bandgap in the spin-up channel near the Fermi level with increasing Cr content, an indication of half-metallicity. 

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2. On the Origin of Abundance Variations in the Milky Way’s High- α Plateau

   https://doi.org/10.3847/1538-4357/ae0b5d  

   Sit, Tawny; Weinberg, David H; Griffith, Emily J (November 2025, The Astrophysical Journal)

   Abstract Using multielement abundances from the Sloan Digital Sky Survey APOGEE survey, we investigate the origin of abundance variations in Milky Way (MW) disk stars on the “high-αplateau,” with −0.5 ≤ [Mg/H] ≤  −0.1 and 0.25 ≤ [Mg/Fe] ≤ 0.35. The elevated [α/Fe] ratios of these stars imply low enrichment contributions from Type Ia supernovae (SN Ia), but it is unclear whether their abundance patterns reflect pure core-collapse supernova (CCSN) enrichment. We find that plateau stars with higher [Fe/Mg] ratios also have higher [X/Mg] ratios for other iron-peak elements, suggesting that the [Fe/Mg] variations in the plateau population do reflect variations in the SN Ia/CCSN ratio. To quantify this finding, we fit the observed abundance patterns with a two-process model, calibrated on the full MW disk, which represents each star’s abundances as the sum of a prompt CCSN process with amplitudeA_ccand a delayed SN Ia process with amplitudeA_Ia. This model is generally successful at explaining the observed trends of [X/Mg] withA_Ia/A_cc, which are steeper for elements with a large SN Ia contribution (e.g., Cr, Ni, Mn) and flatter for elements with low SN Ia contribution (e.g., O, Si, Ca). Our analysis does not determine the value of [Mg/Fe] corresponding to pure CCSN enrichment, but it should be at least as high as the upper edge of the plateau at [Mg/Fe] ≈ 0.35, and could be significantly higher. Compared to the two-process predictions, the observed trends of [X/Mg] withA_Ia/A_ccare steeper for (C+N) but shallower for Ce, providing intriguing but contradictory clues about asymptotic giant branch enrichment in the early disk. 

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3. Abundance Analysis of Stars at Large Radius in the Sextans Dwarf Spheroidal Galaxy*

   https://doi.org/10.3847/1538-4357/ace3c1  

   Roederer, Ian U.; Pace, Andrew B.; Placco, Vinicius M.; Caldwell, Nelson; Koposov, Sergey E.; Mateo, Mario; Olszewski, Edward W.; Walker, Matthew G. (August 2023, The Astrophysical Journal)

   Abstract We present the stellar parameters and chemical abundances of 30 elements for five stars located at large radii (3.5–10.7 times the half-light radius) in the Sextans dwarf spheroidal galaxy. We selected these stars using proper motions, radial velocities, and metallicities, and we confirm them as metal-poor members of Sextans with −3.34 ≤ [Fe/H] ≤ −2.64 using high-resolution optical spectra collected with the Magellan Inamori Kyocera Echelle spectrograph. Four of the five stars exhibit normal abundances of C (−0.34 ≤ [C/Fe] ≤ + 0.36), mild enhancement of theαelements Mg, Si, Ca, and Ti ([α/Fe] = +0.12 ± 0.03), and unremarkable abundances of Na, Al, K, Sc, V, Cr, Mn, Co, Ni, and Zn. We identify three chemical signatures previously unknown among stars in Sextans. One star exhibits large overabundances ([X/Fe] > +1.2) of C, N, O, Na, Mg, Si, and K, and large deficiencies of heavy elements ([Sr/Fe] = −2.37 ± 0.25, [Ba/Fe] = −1.45 ± 0.20, [Eu/Fe] < + 0.05), establishing it as a member of the class of carbon-enhanced metal-poor stars with no enhancement of neutron-capture elements. Three stars exhibit moderate enhancements of Eu (+0.17 ≤ [Eu/Fe] ≤ + 0.70), and the abundance ratios among 12 neutron-capture elements are indicative ofr-process nucleosynthesis. Another star is highly enhanced in Sr relative to heavier elements ([Sr/Ba] = +1.21 ± 0.25). These chemical signatures can all be attributed to massive, low-metallicity stars or their end states. Our results, the first for stars at large radius inSextans, demonstrate that these stars were formed in chemically inhomogeneous regions, such as those found in ultra-faint dwarf galaxies. 

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4. Noncollinear polar magnet Fe2(SeO3)3(H2O)3 with inequivalent Fe3+ sites

   https://doi.org/10.1063/5.0241243  

   Oyeka, Ebube E; Huai, Xudong; Marshall, Madalynn; Winiarski, Michał J; Błachowski, Artur; Cao, Huibo; Tran, Thao T (December 2024, APL Materials)

   The emergence of novel magnetic states becomes more likely when the inversion symmetry of the crystal field, relative to the center between two spins, is broken. We propose that placing magnetic spins in inequivalent sites in a polar lattice can promote a realization of nontrivial magnetic states and associated magnetic properties. To test our hypothesis, we study Fe2(SeO3)(H2O)3 as a model system that displays two distinct Fe(1) and Fe(2) magnetic sites in a polar structure (R3c space group). At low fields μ0H≤ 0.06 T, the material undergoes an antiferromagnetic ordering with TN1 = 77 K and a second transition at TN2≈ 4 K. At μ0H≥ 0.06 T and 74 K ≤T≤ 76 K, a positive entropy change of ∼0.12 mJ mol−1 K−1 can be associated with a metamagnetic transition to possibly nontrivial spin states. At zero field, Fe(1) is nearly fully ordered at T≈ 25 K, while Fe(2) features magnetic frustration down to T = 4 K. The magnetic ground state, a result corroborated by single-crystal neutron diffraction and 57Fe Mössbauer spectroscopy, is a noncollinear antiparallel arrangement of ferrimagnetic Fe(1)–Fe(2) dimers along the c-axis. The results demonstrate that placing distinct magnetic sites in a polar crystal lattice can enable a new pathway to modifying spin, orbital, and lattice degrees of freedom for unconventional magnetism. 

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5. Anderson critical metal phase in trivial states protected by average magnetic crystalline symmetry

   https://doi.org/10.1038/s41467-024-47467-2  

   Wang, Fa-Jie; Xiao, Zhen-Yu; Queiroz, Raquel; Bernevig, B Andrei; Stern, Ady; Song, Zhi-Da (December 2024, Nature Communications)

   Abstract Transitions between distinct obstructed atomic insulators (OAIs) protected by crystalline symmetries, where electrons form molecular orbitals centering away from the atom positions, must go through an intermediate metallic phase. In this work, we find that the intermediate metals will become a scale-invariant critical metal phase (CMP) under certain types of quenched disorder that respect the magnetic crystalline symmetries on average. We explicitly construct models respecting averageC_2zT, m, andC_4zTand show their scale-invariance under chemical potential disorder by the finite-size scaling method. Conventional theories, such as weak anti-localization and topological phase transition, cannot explain the underlying mechanism. A quantitative mapping between lattice and network models shows that the CMP can be understood through a semi-classical percolation problem. Ultimately, we systematically classify all the OAI transitions protected by (magnetic) groups$$Pm,P{2}^{{\prime} },P{4}^{{\prime} }$$ $Pm,P{2}^{\prime },P{4}^{\prime }$, and$$P{6}^{{\prime} }$$ $P{6}^{\prime }$with and without spin-orbit coupling, most of which can support CMP. 

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