Electronic and magnetic properties of FeCr2O4 nanoparticles by advanced synchrotron based soft X-ray magnetic circular dichroism

Origin of Enhancement of Orbital Magnetic Moment in SiO2-Coated Fe3O4 Nanocomposites Studied by X-ray Magnetic Circular Dichroism

“…Figure indicates that there is no such significant shifting found in the spectra of S-0 as considered with other SiO 2 -coated S-1, S-2, S-3, S-4, and S-5 samples except a decrement in the t 2g /e g ratio signifying the changes occurred at the local environment. The features indicated as A, B, and C are found to exhibit similarity with the XAS spectral features of Fe 3 O 4 published previously. ,,,− The spectral feature specified as A at the pre-edge (below ∼532 eV) indicates the transition from the unoccupied states of O 1s to O 2p–Fe 3d hybridized states, specifying chief localization at Fe sites. The prepeak of the samples split in two peaks A 1 and A 2 with energy regions at 530.4 and 531.5 eV, which verifies t 2g and e g states having π and σ characteristics, respectively, following the ligand field theory.…”

“…To determine the orbital and spin magnetic moments separately with an element-specific probe, XAS and XMCD techniques were employed. Unlike VSM, SQUID, and any other magnetometric measurements, to extract the spin and orbital magnetic moments individually and to learn more about the causes of their electronic and magnetic appearance, element-specific techniques called XAS and XMCD become more helpful. ,,,,− At first, soft X-ray absorption spectroscopy (XAS) was recorded by scanning the energy range across 690 to 735 eV at the Fe L 2,3 edges for all the samples. Figure a shows the normalized XAS spectra (i.e., scriptm + + scriptm − 2 ) of Fe 3 O 4 and SiO 2 @Fe 3 O 4 (S-0 to S-5, as indicated) NCs, where m + refers to the positive and m – to the negative helicities of the polarized light.…”

“…The characteristic peaks around h ν = 709.2 and 720.1 eV, which are involved in absorptions at j = 3 2 (L 3 ) and 1 2 (L 2 ) components gathered from Fe 2p core levels, respectively. The spin ( M spin ) and orbital ( M orb ) magnetic moments are determined from the sum rules − ,− where I L 2 (or I L 3 ) and Δ I L 2 (or Δ I L 3 ) are indicated to be the L 2 (or L 3 ) edge integrated XAS and XMCD intensities as mentioned in Figure e,f. Figure d shows the Fe XMCD spectra of sample S-3 measured at 1 T. Δ m = m + – m – refers to the difference in intensities between the two opposite helicities found from the normalized XAS signals.…”

“…In comparison to this XMCD spectrum with the spectrum of Fe 3 O 4 thin films, one would conclude that the bigger negative peak is attributed to the Fe 2+ oxidation state. After removing the contributions generated from the experimental XAS and XMCD spectra of FeO, the XMCD sum rules ,− were used to calculate the effective spin magnetic moment ( M spin eff ). The estimated values for M spin eff are 3.9 to 4.6 μ B /Fe, which were obtained after the summation of the spin moment with magnetic dipole moments.…”

Chromium‐Induced High Covalent Co–O Bonds for Efficient Anodic Catalysts in PEM Electrolyzer

“…[ 13 ] Chromium (Cr), with multiple oxidation states, presumably can be utilized to facilitate the generation of the active sites. [ 9 , 14 ] Moreover, doping Cr is beneficial for regulating the filling state of e g electrons of transition metals (TM), contributing to the hybridization between TM 3d‐O 2p, [ 15 ] which is generally relevant with a high degree of TM–O covalency. We propose that introducing Cr into Co 3 O 4 can optimize the ratio of Co 2+ and Co 3+ , enhance the covalency of Co–O bonds, and accelerate the pre‐oxidation process, thereby achieving low voltage and high stability in PEMWE ( Figure 1 a ).…”