Nanomaterials

Binary Fe-containing LDHs and structurally related layered hydroxides are being widely investigated as adsorbents, catalysts, and redox-active nanomaterials. Yet, links among coprecipitation, phase formation, nanostructure, and reactive-site accessibility remain inconsistently interpreted. This critical review evaluates studies published mainly from 2015 to July 2026 on CoFe, NiFe, MgFe, ZnFe, MnFe, CuFe, and CaFe layered hydroxides and Fe(II)/Fe(III) green rust. Coprecipitation is not a single standardized route: local supersaturation, reagent delivery, mixing, complexation, atmosphere, interlayer chemistry, and aging can alter metal incorporation and phase development, while Fe-rich transient precursors may participate under system-specific conditions. The commonly cited Fe(III) fraction of x = 0.20–0.33 is an empirical guideline rather than a universal stability window, and conventional M(II)-Fe(III) LDHs, CaFe hydrocalumite-/AFm-related phases, and green rust require distinct crystal-chemical interpretations. Nominal composition and LDH-like diffraction cannot establish homogeneous cation incorporation or phase purity. In contrast, diffraction broadening, BET area, nanosheet dimensions, and XPS fitting do not provide stand-alone evidence of defects or accessible reactive sites. Progress toward predictive synthesis requires standardized reporting, system-specific synthesis–composition–phase maps, time-resolved studies, quantitative structure–accessibility relationships, and recognition of as-synthesized, working, recovered, and regenerated materials as potentially distinct structural states, supported by uncertainty analysis, negative outcomes, and validation across laboratories.

Low magnetic damping and narrow ferromagnetic resonance (FMR) linewidth are essential for efficient spin-wave excitation in magnonic devices. We investigate how a combination of deposition techniques, interface engineering, and consequent thermal treatment affects magnetic losses in thin permalloy (Py, Ni₈₀Fe₂₀) films prepared by electron-beam evaporation and magnetron sputtering. Broadband vector network analyzer FMR, atomic force microscopy, and electromagnetic simulations were used to correlate linewidth, surface morphology, and spin-wave excitation. Comparable minimum linewidths were reached by both deposition routes: approximately 23 Oe at 4 GHz for the best electron-beam-evaporated film and approximately 21 Oe for a 20 nm TaN/Py/TaN structure. Electron-beam-evaporated films proved sensitive to substrate choice, surface preparation and—in the absence of plasma cleaning—deposition temperature, whereas the magnetic field applied during growth had only a weak effect. After magnetic annealing, however, only the TaN-encapsulated structure retained its narrow linewidth, while the uncapped films broadened substantially. Simulations further showed that linewidth reduction enhances the excitation efficiency and visibility of standing spin-wave modes. These results indicate that comparable losses are achievable through several process routes, whereas retaining them through thermal processing requires interface engineering—a distinction that matters for integrating Py films into magnonic and spintronic devices.

HfO₂-based ferroelectrics have extended a familiar CMOS high-κ dielectric into a materials platform for nonvolatile memory, low-power logic, and in-memory hardware. This review examines thickness engineering in hafnia, especially Hf_0.5Zr_0.5O₂ (HZO), through the state produced during fabrication, the voltage and time available for switching, and the signal retained during operation. Representative quantitative comparisons retain stack, anneal, electrical state, and endpoint definitions; they show that conditioning and drive voltage can change the apparent thickness trend substantially. Capacitor memory, FeFETs, tunnel junctions, negative-capacitance transistors, and computing devices are compared through architecture-specific read margins and failure criteria. The main unresolved challenge is to isolate thickness effects from coupled process and interface changes and establish reproducible, device-specific operating windows.