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1. Morphogenesis of spin cycloids in a noncollinear antiferromagnet

   https://doi.org/10.1073/pnas.2423298122  

   Ojha, Shashank Kumar; Pal, Pratap; Prokhorenko, Sergei; Husain, Sajid; Ramesh, Maya; Li, Xinyan; Kang, Deokyoung; Meisenheimer, Peter; Schlom, Darrell G; Stevenson, Paul; et al (April 2025, Proceedings of the National Academy of Sciences)

   Pattern formation in spin systems with continuous-rotational symmetry (CRS) provides a powerful platform to study emergent complex magnetic phases and topological defects in condensed-matter physics. However, its understanding and correlation with unconventional magnetic order along with high-resolution nanoscale imaging are challenging. Here, we employ scanning nitrogen vacancy (NV) magnetometry to unveil the morphogenesis of spin cycloids at both the local and global scales within a single ferroelectric domain of (111)-oriented BiFeO₃, which is a noncollinear antiferromagnet, resulting in formation of a glassy labyrinthine pattern. We find that the domains of locally oriented cycloids are interconnected by an array of topological defects and exhibit isotropic energy landscape predicted by first-principles calculations. We propose that the CRS of spin-cycloid propagation directions within the (111) drives the formation of the labyrinthine pattern and the associated topological defects such as antiferromagnetic skyrmions. Unexpectedly, reversing the as-grown ferroelectric polarization from [ $\stackrel{ ¯}{1}$ $\overline{1}$ $\overline{1}$] to [111] produces a noncycloidal NV image contrast which could be attributed to either the emergence of a uniformly magnetized state or a reversal of the cycloid polarity. These findings highlight that (111)-oriented BiFeO₃is not only important for studying the fascinating subject of pattern formation but could also be utilized as an ideal platform for integrating novel topological defects in the field of antiferromagnetic spintronics. 

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2. Magnetic order in nanogranular iron germanium (Fe _0.53 Ge _0.47 ) films

   https://doi.org/10.1088/1361-648X/ad8c0a  

   Zielinski, Ruthi; Nguyen, Nhat; Herrington, Bryce; Tarkian, Amir; Taha, Omar; Chin, Wai_Kiat; Mahmood, Ather; Chen, Xiaoqian; Klewe, Christoph; Shafer, Padraic; et al (November 2024, Journal of Physics: Condensed Matter)

   Abstract We study the effect of strain on the magnetic properties and magnetization configurations in nanogranular Fe_xGe ${}_{1-x}$films ( $x=0.53\pm 0.05$) with and without B20 FeGe nanocrystals surrounded by an amorphous structure. Relaxed films on amorphous silicon nitride membranes reveal a disordered skyrmion phase while films near and on top of a rigid substrate favor ferromagnetism and an anisotropic hybridization of Fedlevels and spin-polarized Gespband states. The weakly coupled topological states emerge at room temperature and become more abundant at cryogenic temperatures without showing indications of pinning at defects or confinement to individual grains. These results demonstrate the possibility to control magnetic exchange and topological magnetism by strain and inform magnetoelasticity-mediated voltage control of topological phases in amorphous quantum materials. 

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3. Local structure elucidation of tungsten-substituted vanadium dioxide (V$$_{1-x}$$W$$_x$$O$$_2$$)

   https://doi.org/10.1038/s41598-022-18575-0  

   Wilson, Catrina E.; Gibson, Amanda E.; Cuillier, Paul M.; Li, Cheng-Han; Crosby, Patrice H. N.; Trigg, Edward B.; Najmr, Stan; Murray, Christopher B.; Jinschek, Joerg R.; Doan-Nguyen, Vicky (August 2022, Scientific Reports)

   Abstract Initially, vanadium dioxide seems to be an ideal first-order phase transition case study due to its deceptively simple structure and composition, but upon closer inspection there are nuances to the driving mechanism of the metal-insulator transition (MIT) that are still unexplained. In this study, a local structure analysis across a bulk powder tungsten-substitution series is utilized to tease out the nuances of this first-order phase transition. A comparison of the average structure to the local structure using synchrotron x-ray diffraction and total scattering pair-distribution function methods, respectively, is discussed as well as comparison to bright field transmission electron microscopy imaging through a similar temperature-series as the local structure characterization. Extended x-ray absorption fine structure fitting of thin film data across the substitution-series is also presented and compared to bulk. Machine learning technique, non-negative matrix factorization, is applied to analyze the total scattering data. The bulk MIT is probed through magnetic susceptibility as well as differential scanning calorimetry. The findings indicate the local transition temperature ($$T_c$$ $T_c$) is less than the average$$T_c$$ $T_c$supporting the Peierls-Mott MIT mechanism, and demonstrate that in bulk powder and thin-films, increasing tungsten-substitution instigates local V-oxidation through the phase pathway VO$$_2\, \rightarrow$$ ${}_2\to$V$$_6$$ ${}_6$O$$_{13} \, \rightarrow$$ ${}_{13}\to$V$$_2$$ ${}_2$O$$_5$$ ${}_5$. 

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4. Modifications of ion beam sputtered tantala thin films by secondary argon and oxygen bombardment

   https://doi.org/10.1364/AO.59.00A150  

   Yang, Le; Randel, Emmett; Vajente, Gabriele; Ananyeva, Alena; Gustafson, Eric; Markosyan, Ashot; Bassiri, Riccardo; Fejer, Martin; Menoni, Carmen (January 2020, Applied Optics)

   Amorphous tantala ( ${\mathrm{T}\mathrm{a}}_2{\mathrm{O}}_5$) thin films were deposited by reactive ion beam sputtering with simultaneous low energy assist ${\mathrm{A}\mathrm{r}}^{+}$or ${\mathrm{A}\mathrm{r}}^{+}/{\mathrm{O}}_2^{+}$bombardment. Under the conditions of the experiment, the as-deposited thin films are amorphous and stoichiometric. The refractive index and optical band gap of thin films remain unchanged by ion bombardment. Around 20% improvement in room temperature mechanical loss and 60% decrease in absorption loss are found in samples bombarded with 100-eV ${\mathrm{A}\mathrm{r}}^{+}$. A detrimental influence from low energy ${\mathrm{O}}_2^{+}$bombardment on absorption loss and mechanical loss is observed. Low energy ${\mathrm{A}\mathrm{r}}^{+}$bombardment removes excess oxygen point defects, while ${\mathrm{O}}_2^{+}$bombardment introduces defects into the tantala films. 

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5. Luminal transport through intact endoplasmic reticulum limits the magnitude of localized Ca ²⁺ signals

   https://doi.org/10.1073/pnas.2312172121  

   Crapart, Cécile C; Scott, Zubenelgenubi C; Konno, Tasuku; Sharma, Aman; Parutto, Pierre; Bailey, David_M D; Westrate, Laura M; Avezov, Edward; Koslover, Elena F (March 2024, Proceedings of the National Academy of Sciences)

   The endoplasmic reticulum (ER) forms an interconnected network of tubules stretching throughout the cell. Understanding how ER functionality relies on its structural organization is crucial for elucidating cellular vulnerability to ER perturbations, which have been implicated in several neuronal pathologies. One of the key functions of the ER is enabling Ca ${}^{2+}$signaling by storing large quantities of this ion and releasing it into the cytoplasm in a spatiotemporally controlled manner. Through a combination of physical modeling and live-cell imaging, we demonstrate that alterations in ER shape significantly impact its ability to support efficient local Ca ${}^{2+}$releases, due to hindered transport of luminal content within the ER. Our model reveals that rapid Ca ${}^{2+}$release necessitates mobile luminal buffer proteins with moderate binding strength, moving through a well-connected network of ER tubules. These findings provide insight into the functional advantages of normal ER architecture, emphasizing its importance as a kinetically efficient intracellular Ca ${}^{2+}$delivery system. 

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