A remarkable hardening ($\sim${}30\,\,cm-1) of the normal mode of vibration associated with the symmetric stretching of the oxygen octahedra for the Ba2FeReO6 and Sr2CrReO6 double perovskites is observed below the corresponding magnetic ordering temperatures. The very large magnitude of this effect and its absence for the antisymmetric stretching mode provide evidence against a conventional spin-phonon coupling mechanism. Our observations are consistent with a collective excitation formed by the combination of the vibrational mode with oscillations of Fe or Cr 3d and Re 5d occupations and spin magnitudes.

Raman scattering experiments on LaFeAsO with distinct antiferromagnetic ($T_{\text{AFM}}=140$ K) and tetragonal-orthorhombic ($T_S=155$ K) transitions show a quasielastic peak (QEP) in $B_{2g}$ symmetry (2 Fe tetragonal cell) that fades away below $\sim T_{\text{AFM}}$ and is ascribed to electronic nematic fluctuations. A scaling of the reported shear modulus with the $T$ dependence of the QEP height rather than the QEP area indicates that magnetic degrees of freedom drive the structural transition. The large separation between $T_S$ and $T_{\text{AFM}}$ in LaFeAsO compared to ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ manifests itself in slower dynamics of nematic fluctuations in the former.

This study investigated the effects of plasma electrolytic oxidation (PEO) treatment in a Ca- and P-rich electrolyte on the surface of the Ti-6Al-4V alloy with distinct α/β phase proportions previously induced by heat treatments. The results revealed that the α/β phase proportions were successfully altered by the heat treatment temperatures, forming α phase plates surrounded by β phase precipitates. PEO-treated samples exhibited a thick and microsized porous TiO₂ coating in the anatase and rutile crystalline forms. The oxide layer was depleted by Al and V atoms, while Ca and P were gradually enriched along the coatings. Chemical analysis also indicated the absorption of water and organic molecules into the outer layer. PEO-treated samples had microscale roughness and thickness, hydrophilic behavior, and surface energy mainly formed by the dispersive component. The bulk’s elastic modulus decreased with β phase precipitation, while the alloying elements directly influenced the Vickers microhardness. The corrosion tests indicated a stable and protective layer in the PEO-treated samples, showing better corrosion resistance than untreated ones. Overall, the findings indicated that the α and β phase proportion significantly impacts the mechanical properties, while the PEO treatment acts in the corrosion protection and surface aspects, suggesting that combining both approaches could be a powerful tool in biomedical applications.

The crystal lattice of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ is investigated with synchrotron x-ray powder diffraction under hydrostatic pressures up to $P=43$ GPa and temperatures down to 20 K. The tetragonal unit cell is maintained over the whole investigated pressure range, within our resolution and sensitivity. The $c$-axis compressibility ${\kappa }_c(P,T)\equiv -(1/c)(dc/dP)$ presents an anomaly with pressure at $P_1=17$ GPa at fixed $T=20$ K that is not observed at $T=300$ K, whereas ${\kappa }_a(P,T)$ is nearly temperature independent and shows a linear behavior with $P$. The anomaly in ${\kappa }_c(P,T)$ is associated with the onset of long-range magnetic order, as evidenced by an analysis of the temperature dependence of the lattice parameters at fixed $P=13.7\pm 0.5$ GPa. At fixed $T=20$ K, the tetragonal elongation $c/a(P,T)$ shows a gradual increment with pressure and a depletion above $P_2=30$ GPa that indicates an orbital transition and possibly marks the collapse of the $J_{\text{eff}}=1/2$ spin-orbit-entangled state. Our results support pressure-induced phase transitions or crossovers between electronic ground states that are sensed, and therefore can be probed, by the crystal lattice at low temperatures in this prototype spin-orbit Mott insulator.

The series of intermetallic compounds $R{\mathrm{NiSi}}_3 (R=\text{rare} \text{earth})$ shows interesting magnetic properties evolving with $R$ and metamagnetic transitions under applied magnetic field for some of the compounds. The microscopic magnetic structures must be determined to rationalize such rich behavior. Here, resonant x-ray magnetic diffraction experiments are performed on single crystals of ${\mathrm{GdNiSi}}_3$ and ${\mathrm{TbNiSi}}_3$ at zero field. The primitive magnetic unit cell matches the chemical cell below the Néel temperatures $T_N=22.2$ and 33.2 K, respectively. The magnetic structure is determined to be the same for both compounds (magnetic space group $Cmm{m}^{\prime }$). It features ferromagnetic $ac$ planes that are stacked in an antiferromagnetic $+-+-$ pattern, with the rare-earth magnetic moments pointing along the $\vec{a}$ direction, which contrasts with the $+--+$ stacking and moment direction along the $\vec{b}$ axis previously reported for ${\mathrm{YbNiSi}}_3$. This indicates a sign reversal of the coupling constant between second-neighbor $R$ planes as $R$ is varied from Gd and Tb to Yb. The long $b$ lattice parameter of ${\mathrm{GdNiSi}}_3$ and ${\mathrm{TbNiSi}}_3$ shows a magnetoelastic expansion upon cooling below $T_N$, pointing to the conclusion that the $+-+-$ stacking is stabilized under lattice expansion. A competition between distinct magnetic stacking patterns with similar exchange energies tuned by the size of $R$ sets the stage for the magnetic ground state instability observed along this series.

Raman scattering, synchrotron x-ray diffraction, specific heat, resistivity and magnetic susceptibility measurements were performed in Sr(Fe _{1− x} Co _x ) ₂ As ₂ [ ] single crystals with superconducting critical temperature K and two additional transitions at 132 and 152 K observed in both specific heat and resistivity data. A quasielastic Raman signal with B _{2 g} symmetry (tetragonal cell) associated with electronic nematic fluctuations is observed. Crucially, this signal shows maximum intensity at K, marking the nematic transition temperature. X-ray diffraction shows evidence of coexisting orthorhombic and tetragonal domains between and ∼ 152 K, implying that precursor orthorhombic domains emerge over an extended temperature range above . While the height of the quasielastic Raman peak is insensitive to , the temperature-dependence of the average nematic fluctuation rate indicates a slowing down of the nematic fluctuations inside the precursor orthorhombic domains. These results are analogous to those previously reported for the LaFeAsO parent oxypnictide (Kaneko et al 2017 Phys. Rev . B 96 014506). We propose a scenario where the precursor orthorhombic phase may be generated within the electronically disordered regime ( ) as long as the nematic fluctuation rate is sufficiently small in comparison to the optical phonon frequency range. In this regime, the local atomic structure responds adiabatically to the electronic nematic fluctuations, creating a net of orthorhombic clusters that, albeit dynamical for , may be sufficiently dense to sustain long-range phase coherence in a diffraction process up to .