Effect of Cationic Disorder on the Magnetic Moment of Sr₂FeMoO₆: Ab Initio Calculations

Abstract

Discrepancies between both theoretical calculations and experimental measurements of the magnetic moment on Fe sites in Sr 2 FeMoO 6 have been accounted for because of disorder effects. In this work, we deepen the repercussions of cationic disorder in the above ferromagnetic compound specially about the interactions between Fe antisites, which are found antiferromagnetic for the most stable systems. An amount of disorder (12.5% and 25%) was introduced within the systems via atomic substitution. Ab initio calculations using the generalized gradient approximation were performed with local Hubbard terms U Fe and U Mo associated with both Fe and Mo sites, respectively. We found a magnetic saturation of 2.99 μ B for a 12.5% amount of disorder and 2.22 μ B in the case of 25% disorder, which is in agreement with neutron magnetic scattering experiments. Half-metallicity is found to remain only for the 12.5% disorder case.

Effect of the itinerant electron density on the magnetization and Curie temperature of Sr2FeMoO6 ceramics

“…1(a) shows all the XRD patterns of C1-C6 ceramics. One can see clearly that all the diffracted peaks of C1-C6 are well consistent with the double perovskite structure with a tetragonal phase and a space group of I4/m, 3,36,37 and no second phases are identied. The superstructure diffraction peak (101) located at approximately 19.8 C has a close correlation with the Fe/Mo ordering degree ( Fig.…”

The Role of the Fe/Mo Cations Ordering Degree and Oxygen Non‐Stoichiometry on the Formation of the Crystalline and Magnetic Structure of Sr2FeMoO6−δ

“…In real crystals, various kinds of zero‐dimensional defects, especially the Mo Fe , Fe Mo antisites and oxygen vacancies V O , induce a distortion of the crystal structure, which leads to a redistribution of the electron density and to the formation of iron and molybdenum cations, Fe 2+ (3 d 6 ) { S = 2} and Mo 6+ (4 d 0 ) { S = 0}, respectively. Diamagnetic Mo 6+ (4 d 0 ) ions do not participate in the exchange interactions, and the latter ones between the Fe 2+ (3 d 6 ) or Fe 3+ (3 d 5 ) ions are necessarily negative, thus producing an antiferromagnetic ordering of the magnetic moments . Therefore, the distortion of the crystal lattice caused by defects in the cation and anion sublattices strongly influences the magnetic and electrical transport properties of strontium ferromolybdate …”

“…One of the main reasons why these materials obtained under similar regimes are not widely used is a low reproducibility of their physical–chemical parameters. This fact indicates a high sensitivity of the compound to the synthesis parameters which affect the variation of δ and P values from sample to sample …”

“…Diamagnetic Mo 6þ (4d 0 ) ions do not participate in the exchange interactions, and the latter ones between the Fe 2þ (3d 6 ) or Fe 3þ (3d 5 ) ions are necessarily negative, thus producing an antiferromagnetic ordering of the magnetic moments. [11,12] Therefore, the distortion of the crystal lattice caused by defects in the cation and anion sublattices strongly influences the magnetic and electrical transport properties of strontium ferromolybdate. [13][14][15] It is known that the critical temperature (T С ) of the paramagnetic-ferrimagnetic transition, the saturation magnetization (M s ), and the electrical resistivity (ρ) are determined by the density of the electronic states N(E) close to the Fermi level (E F ).…”

“…This fact indicates a high sensitivity of the compound to the synthesis parameters which affect the variation of δ and P values from sample to sample. [6][7][8][9][10][11][12][13][14] Thus, the motivation of the present work is rooted in the necessity to establish a correlation between the oxygen nonstoichiometry and the degree of superstructural ordering of the iron and molybdenum cations in SFMO with the aim of obtaining samples possessing optimum magnetic and electrical transport characteristics.…”