ProbingMocore valence onSr2FeMoO6half-metallic ferromagnets and the

Abstract

By using photoemission spectroscopy we explore the modifications of Mo core levels upon electron filling the conduction band in the half-metallic ferromagnetic Sr 2−x La x FeMoO 6 ͑x = 0 to 0.6͒ oxides. The 3d-core level Mo spectra of undoped ͑x =0͒ samples reveal the presence of Mo 6+ :Mo 5+ states in its ground state. Upon La doping, it is found that the 3d 5/2 -3d 3/2 Mo 5+ doublet progressively emerges and grows in intensity. It is interpreted as a signature of the electron injection into Mo-based orbitals. The observation of distinguishable Mo 6+ :Mo 5+ states may have severe implications on current understanding of the microscopic origin of the ferromagnetic coupling in these oxides and on suggestions of a negative effective Coulomb interaction at Mo atoms and electronic phase separations.

Magnetic properties of fine SFMO particles: Superparamagnetism

“…The m eff value calculated from the valence distribution observed by XPS[6] is 5:3 m B , which is in excellent agreement with the value obtained here. For sample A we get m eff ¼ 3:0 m B and y p ¼ 360 K. Lowered m eff values have previously been explained by itinerant electrons XRD measurement (crosses) and Rietveld refinement (line) for sample A. Antisite disorder is 10%, average SFMO grain size is 31.1 nm and w 2 for the refinement is 1.72.…”

“…A lot of discussion has risen about the mechanism of TMR in SFMO, where the exchange route is Fe-O-Mo. With photoemission spectroscopy and Mo¨ssbauer it has been verified that in pure SFMO the Mo atoms have a superposition of 5þ and 6þ valences and Fe have valences between 2þ and 3þ [5,6]. The effect of antisite disorder on the MR in SFMO has also been studied extensively [7,8].…”

Signature of an antiferromagnetic metallic ground state in heavily electron-doped Sr2FeMoO6

“…It should be noted that the growth of the AFM-like magnetic state is not proportional to the available Fe-O-Fe AFM connections, which in fact decreases for compositions with x >1. 25. This establishes that the observed crossover in magnetic behavior is entirely guided by changes in the electronic structure as a result of gain in kinetic energy, 3 and is uncorrelated to Fe-O-Fe superexchange, effective in the Fe-rich regions.…”

Nanocrystalline Sr2FeMoO6 prepared by citrate-gel method

“…In practice, antisite (AS) disorder, the mixing of Fe and Mo atoms, is found to quite often to be present in SFMOsamples and it affects very strongly the magnetic properties and MR of SFMO [3][4][5]. Usually Fe has a valence of þ3 in perovskites structures but valence mixing of Fe 3þ =Fe 2þ and Mo 5þ =Mo 6þ has been observed in SFMO [6,7]. The B 0 and B 00 sites are antiferromagnetically coupled and in case of Fe 3þ and Mo 5þ should give a net moment of 4m B , but experiments have given values clearly less than 4m B which is due to the AS disorder [3,4] and the itinerant electrons [8].…”