Metal–insulator transition in NiS_2−xSe_x: chemical vs external pressure effects

Abstract

The Se alloying (x)-and the pressure (P)-induced metal-insulator transitions on the strongly correlated NiS 2−x Se x system have been investigated through Raman and infrared (IR) spectroscopies. Raman and IR responses of NiS 2 to lattice compression are correlated to a metallization transition, occurring at ∼4 GPa. This result suggests a strong interaction between lattice and electronic degrees of freedom. In particular, IR measurements carried out by applying P on NiS 2 (i.e. lattice contraction) and on Se alloying (i.e. lattice expansion) reveal that in both cases a metallic state is obtained. Our optical spectroscopy results deviate from the idea of a simple scaling factor between P and x previously claimed by transport measurements, but, on the contrary, point out the substantially different microscopic origin of the two transitions.

Magnetochromic sensing and size-dependent collective excitations in iron oxide nanoparticles

“…We assign the broad absorption band centered at 11,600 cm −1 as the 6 A 1g → 4 T 1g Fe 3+ on-site excitation [19] and the smaller feature on the leading edge of this structure (at 10,470 cm −1 ) as a magnon sideband.…”

“…This system displays a spinflop transition that is driven by both temperature (T M = 263 K) and magnetic field (H SF = 6 and 16 T for the easy and hard axis, respectively). [16][17][18] Applied field creates color contrast (red → red ′ ) via a spin-charge coupling mechanism by amplifying changes in the 6 A 1g → 4 T 1g on-site excitation across the spin-flop transition. [19,20] Analysis of the collective excitations on the leading edge of the d-tod transition also reveals magnetic symmetry.…”