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1. Kinetically Controlled Growth of Sub‐Millimeter 2D Cs ₂ SnI ₆ Nanosheets at the Liquid–Liquid Interface

   https://doi.org/10.1002/smll.202006279  

   Zhu, Weiguang; Shen, Junhua; Li, Mingxin; Yang, Kun; Bu, Wei; Sun, Yi‐Yang; Shi, Jian; Lian, Jie (December 2020, Small)

   Abstract Cs₂SnI₆perovskite displays excellent air stability and a high absorption coefficient, promising for photovoltaic and optoelectronic applications. However, Cs₂SnI₆‐based device performance is still low as a result of lacking optimized synthesis approaches to obtain high quality Cs₂SnI₆crystals. Here, a new simple method to synthesize single crystalline Cs₂SnI₆perovskite at a liquid–liquid interface is reported. By controlling solvent conditions and Cs₂SnI₆supersaturation at the liquid–liquid interface, Cs₂SnI₆crystals can be obtained from 3D to 2D growth with controlled geometries such as octahedron, pyramid, hexagon, and triangular nanosheets. The formation mechanisms and kinetics of complex shapes/geometries of high quality Cs₂SnI₆crystals are investigated. Freestanding single crystalline 2D nanosheets can be fabricated as thin as 25 nm, and the lateral size can be controlled up to sub‐millimeter regime. Electronic property of the high quality Cs₂SnI₆2D nanosheets is also characterized, featuring a n‐type conduction with a high carrier mobility of 35 cm²V⁻¹s⁻¹. The interfacial reaction‐controlled synthesis of high‐quality crystals and mechanistic understanding of the crystal growth allow to realize rational design of materials, and the manipulation of crystal growth can be beneficial to achieve desired properties for potential functional applications. 

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2. Low‐Voltage Magnetoelectric Coupling in Fe _0.5 Rh _0.5 /0.68PbMg _1/3 Nb _2/3 O ₃ ‐0.32PbTiO ₃ Thin‐Film Heterostructures

   https://doi.org/10.1002/adfm.202105068  

   Zhao, Wenbo; Kim, Jieun; Huang, Xiaoxi; Zhang, Lei; Pesquera, David; Velarde, Gabriel_A_P; Gosavi, Tanay; Lin, Chia‐Ching; Nikonov, Dmitri_E; Li, Hai; et al (July 2021, Advanced Functional Materials)

   Abstract The rapid development of computing applications demands novel low‐energy consumption devices for information processing. Among various candidates, magnetoelectric heterostructures hold promise for meeting the required voltage and power goals. Here, a route to low‐voltage control of magnetism in 30 nm Fe_0.5Rh_0.5/100 nm 0.68PbMg_1/3Nb_2/3O₃‐0.32PbTiO₃(PMN‐PT) heterostructures is demonstrated wherein the magnetoelectric coupling is achieved via strain‐induced changes in the Fe_0.5Rh_0.5mediated by voltages applied to the PMN‐PT. We describe approaches to achieve high‐quality, epitaxial growth of Fe_0.5Rh_0.5on the PMN‐PT films and, a methodology to probe and quantify magnetoelectric coupling in small thin‐film devices via studies of the anomalous Hall effect. By comparing the spin‐flop field change induced by temperature and external voltage, the magnetoelectric coupling coefficient is estimated to reach ≈7 × 10⁻⁸ s m⁻¹at 325 K while applying a −0.75 V bias. 

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3. Magnetotransport Anomaly in Room‐Temperature Ferrimagnetic NiCo ₂ O ₄ Thin Films

   https://doi.org/10.1002/adma.201805260  

   Chen, Xuegang; Zhang, Xiaozhe; Han, Myung‐Geun; Zhang, Le; Zhu, Yimei; Xu, Xiaoshan; Hong, Xia (November 2018, Advanced Materials)

   Abstract The inverse spinel ferrimagnetic NiCo₂O₄presents a unique model system for studying the competing effects of crystalline fields, magnetic exchange, and various types of chemical and lattice disorder on the electronic and magnetic states. Here, magnetotransport anomalies in high‐quality epitaxial NiCo₂O₄thin films resulting from the complex energy landscape are reported. A strong out‐of‐plane magnetic anisotropy, linear magnetoresistance, and robust anomalous Hall effect above 300 K are observed in 5–30 unit cell NiCo₂O₄films. The anomalous Hall resistance exhibits a nonmonotonic temperature dependence that peaks around room temperature, and reverses its sign at low temperature in films thinner than 20 unit cells. The scaling relation between the anomalous Hall conductivity and longitudinal conductivity reveals the intricate interplay between the spin‐dependent impurity scattering, band intrinsic Berry phase effect, and electron correlation. This study provides important insights into the functional design of NiCo₂O₄for developing spinel‐based spintronic applications. 

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4. Infrared-active phonon modes and static dielectric constants in α -(Al _x Ga _{1− x} ) ₂ O ₃ (0.18  ≤ x  ≤ 0.54) alloys

   https://doi.org/10.1063/5.0085958  

   Stokey, Megan; Gramer, Teresa; Korlacki, Rafał; Knight, Sean; Richter, Steffen; Jinno, Riena; Cho, Yongjin; Xing, Huili Grace; Jena, Debdeep; Hilfiker, Matthew; et al (March 2022, Applied Physics Letters)

   We determine the composition dependence of the transverse and longitudinal optical infrared-active phonon modes in rhombohedral α-(Al_xGa_1−x)₂O₃alloys by far-infrared and infrared generalized spectroscopic ellipsometry. Single-crystalline high quality undoped thin-films grown on m-plane oriented α-Al₂O₃substrates with x =  0.18, 0.37, and 0.54 were investigated. A single mode behavior is observed for all phonon modes, i.e., their frequencies shift gradually between the equivalent phonon modes of the isostructural binary parent compounds. We also provide physical model line shape functions for the anisotropic dielectric functions. We use the anisotropic high-frequency dielectric constants for polarizations parallel and perpendicular to the lattice c axis measured recently by Hilfiker et al. [Appl. Phys. Lett. 119, 092103 (2021)], and we determine the anisotropic static dielectric constants using the Lyddane–Sachs–Teller relation. The static dielectric constants can be approximated by linear relationships between those of α-Ga₂O₃and α-Al₂O₃. The optical phonon modes and static dielectric constants will become useful for device design and free charge carrier characterization using optical techniques. 

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5. Electronic-grade epitaxial (111) KTaO ₃ heterostructures

   https://doi.org/10.1126/sciadv.adk4288  

   Kim, Jieun; Yu, Muqing; Lee, Jung-Woo; Shang, Shun-Li; Kim, Gi-Yeop; Pal, Pratap; Seo, Jinsol; Campbell, Neil; Eom, Kitae; Ramachandran, Ranjani; et al (May 2024, Science Advances)

   KTaO₃heterostructures have recently attracted attention as model systems to study the interplay of quantum paraelectricity, spin-orbit coupling, and superconductivity. However, the high and low vapor pressures of potassium and tantalum present processing challenges to creating heterostructure interfaces clean enough to reveal the intrinsic quantum properties. Here, we report superconducting heterostructures based on high-quality epitaxial (111) KTaO₃thin films using an adsorption-controlled hybrid PLD to overcome the vapor pressure mismatch. Electrical and structural characterizations reveal that the higher-quality heterostructure interface between amorphous LaAlO₃and KTaO₃thin films supports a two-dimensional electron gas with substantially higher electron mobility, superconducting transition temperature, and critical current density than that in bulk single-crystal KTaO₃-based heterostructures. Our hybrid approach may enable epitaxial growth of other alkali metal–based oxides that lie beyond the capabilities of conventional methods. 

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