Enhanced magnetism of Fe3O4 nanoparticles with Ga doping

Abstract

Magnetic (Ga x Fe 1Àx ) 3 O 4 nanoparticles with 5%-33% gallium doping (x ¼ 0.05-0.33) were measured using x-ray absorption spectroscopy and x-ray magnetic circular dichroism to determine that the Ga dopant is substituting for Fe 3þ as Ga 3þ in the tetrahedral A-site of the spinel structure, resulting in an overall increase in the total moment of the material. Frequency-dependent alternating-current magnetic susceptibility measurements showed these particles to be weakly interacting with a reduction of the cubic anisotropy energy term with Ga concentration. The element-specific dichroism spectra show that the average Fe moment is observed to increase with Ga concentration, a result consistent with the replacement of A-site Fe by Ga.

Properties of Ga-Doped Magnetite Nanoparticles

“…Because in pure bulk magnetite I(B)/I(A) = 2 (assuming the Lamb factor f (A) = f (B)) the simplest explanation of our results lead to the conclusion that Ga atoms are located preferentially in B position for sample when Ga 0.2 Fe 2.8 O 4 is in core and almost evenly distributed in the case when Ga 0.2 Fe 2.8 O 4 is in the shell. This is in contradiction with the conclusion obtained from our X-ray measurements and literature [7]. This simple analysis does not take into account the influence of preparation method on the properties of magnetite nanoparticles.…”

“…Such a model was discussed in detail in Ref. [7]. The model with the A-B disorder and untouched oxygen positions had also to be considered.…”

“…Another important aspect is preventing nanoparticles agglomeration, that is easier to achieve in the coreshell system Fe 3 O 4 /Ga 0.2 Fe 2.8 O 4 . According to X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements carried out on (Ga x Fe 1−x ) 3 O 4 nanoparticles with (x = 0.05-0.33) gallium doping, the average Fe moment is observed to increase resulting in an overall increase in the total moment of the material [7]. In fact, an admixture of Ga 3+ at Fe 3 O 4 as the nonmagnetic ions located at the tetrahedral sites no longer partially cancel the magnetic moment of iron ions in the octahedral sites.…”

What is the correct Fe L23 X-ray absorption spectrum of magnetite?

“…Thus, the additional peak at 708 eV in the Fe L 23 XAS spectra of as-received Sigma-Aldrich nanomagnetite is caused by partial oxidization. Thus we assume that similar peaks observed in the Fe L 3 -edge XAS of Fe 3 O 4 reported by Garcia et al [21] and Pool et al [26] (among others) are also due to partial oxidation, either at the surface, and sensed preferentially due to the TEY detection, or from the bulk, due to a non-stoichiometric synthesis or the overall sample being partially oxidized. Fig.…”

Determination of the electronic and structural configuration of coordination compounds by synchrotron-radiation techniques

“…Consequently, XMCD is a major characterization tool for ferromagnetic metals, oxides and their surfaces, as well as for paramagnetic sites in bio-inorganic chemistry and coordination compounds [772]. The technique was able to bring new insight in the investigation of transition metal supported catalysts [582,773,774] and in bio-catalysis [775]. Usually, the XMCD measurement are performed at cryogenic temperatures and the XMCD signals are followed either by varying the magnetic field at constant temperature or by varying the temperature at fixed magnetic field [776].…”