Evidence of strong antiferromagnetic coupling between localized and itinerant electrons in ferromagneticSr2FeMoO6

Abstract

Magnetic dc susceptibility (χ) and electron spin resonance (ESR) measurements in the paramagnetic regime, are presented. We found a Curie-Weiss (CW) behavior for χ(T) with a ferromagnetic Θ = 446(5) K and µ ef f = 4.72(9)µ B /f.u., this being lower than that expected for either F e 3+ (5.9µ B ) or F e 2+ (4.9µ B ) ions. The ESR g-factor g = 2.01(2), is associated with F e 3+ .We obtained an excellent description of the experiments in terms of two interacting sublattices: the localized F e 3+ (3d 5 ) cores and the delocalized electrons. The coupled equations were solved in a mean-field approximation, 1 assuming for the itinerant electrons a bare susceptibility independent on T .We obtained χ 0 e = 3.7 10 −4 emu/mol. We show that the reduction of µ ef f for F e 3+ arises from the strong antiferromagnetic (AFM) interaction between the two sublattices. At variance with classical ferrimagnets, we found that Θ is ferromagnetic. Within the same model, we show that the ESR spectrum can be described by Bloch-Hasegawa type equations. Bottleneck is evidenced by the absence of a g-shift. Surprisingly, as observed in CMR manganites, no narrowing effects of the ESR linewidth is detected in spite of the presence of the strong magnetic coupling. These results provide evidence that the magnetic order in Sr 2 F eM oO 6 does not originates in superexchange interactions, but from a novel mechanism recently proposed for double perovskites.PACS: 75.10. 76.60.Es, 75.30.Vn

Phase diagram and influence of defects in the double perovskites

“…[3][4][5][6][7][8][9][10][11][12][13][14][15] The magnetism of these compounds arises from the Fe 3ϩ , Sϭ5/2 core spin, while the charge state of the Mo ion is 5 ϩ. Spatially, the Mo and Fe ions occupy two interleaving fcc lattices ͑sodium chloride structure͒. The conduction band contains one electron per unit cell, which tends to be antiparallel to the Fe spin.…”

Stabilization of cubic Sr2FeMoO6 through topochemical reduction

“…2,3 Electron doping has been identified as a promising method to increase the magnetic ordering temperature in double perovskites such as SFMO. 4 However, traditional cation solidsolution techniques tend to induce lattice strain. This strain has been linked to B-site disorder, or anti-site disorder (ASD), and is therefore detrimental to long range magnetic ordering.…”

“…Pellets of the reaction mixture were then sealed in glass ampoules (pressure <10 −2 Torr) and heated in a box furnace at 500 • C for 3 days followed by furnace cooling. The reacted mixture was then washed with 0.15 M (mol/L) NH 4 Cl/dried methanol to remove reaction byproducts. The tetragonal to cubic phase transition was observed in samples reduced at temperatures as low as 400 • C. However, in order to maximize the effects of the reaction, the highest reaction temperature that did not lead to sample decomposition (500 • C) was used for all subsequent characterization experiments.…”

Crystal structural, magnetic, and electrical transport properties of Sr1.1K0.9FeMoO6 double perovskite

“…The magnetic structure of this oxide was originally [1] described as resulting from an antiferromagnetic coupling between Fe-d 5 and Mo-4d 1 electrons, in a ferrimagnetic-like structure. However, recent reports indicating that the dominant magnetic interaction in the system is ferromagnetic [2,3] and that the magnetic moment of Mo ions is small [4,5] have forced a review of the picture. In fact, the observations of a substantial low-field magnetoresistance (MR) [1] and that electrical resistivity appears to be correlated with the Curie temperature [6] suggested that charge carriers have a dominant role in the magnetic coupling.…”

“…Tovar et al [3] proposed that the ferromagnetic coupling is mediated by the itinerant carriers (electrons) at the Fermi level much as in conventional Ruderman-Kittel-KasuyaYosida (RKKY) itinerant ferromagnets or in diluted magnetic semiconductors [7]. From that picture, a natural suggestion to increase the Curie temperature emerged and it was proposed that increasing the carrier density may lead to a change of the density of states at the Fermi level, and a [14].…”