Synthesis and magnetic characterisation of Fe_1−xMg_xSb₂O₄ (x = 0.25, 0.50, 0.75) and their oxygen-excess derivatives, Fe_1−xMg_xSb₂O_4+y

Abstract

The structures and magnetic properties of Fe1−xMgxSb2O4 and their products from low-temperature oxidation, Fe1−xMgxSb2O4+y, are described.

Magnetic interactions in Fe1−xMxSb2O4, M = Mg, Co, deduced from Mössbauer spectroscopy

“…The spectra shown in Fig. 2 have already been reported [18] but are reproduced here to assist this new discussion in terms of the magnetic interactions in these materials. Fig.…”

“…At a given temperature below the magnetic ordering temperature (T N , ca. 45 K [3,4,15,18]) isolated iron ions will be more likely to behave paramagnetically while long strings of iron ions will retain magnetic order. This model thus predicts different magnetic behaviour coexisting in the magnetically ordered temperature range because of the different segment lengths.…”

“…We have also prepared new phases involving substitution on the M site. The magnetic moments deduced from neutron diffraction and magnetic susceptibility measurements in the series of composition Fe 1−x Co x Sb 2 O 4 suggested the existence of some short range correlations within the chains [17] whilst in materials of formulation Fe 1−x Mg x Sb 2 O 4 , the decrease in magnetic ordering temperature with increasing concentrations of magnesium was associated with non-magnetic Mg 2+ ions weakening the magnetic interactions between Fe 2+ ions [18]. An interesting feature of these materials has been the demonstration of their capacity to accommodate additional oxygen within their structures [19].…”

57Fe Mössbauer spectra from fluorinated phases of Fe0.50M0.50(M = Co,Mg)Sb2O4

“…Materials of composition Mg 0.50 Fe 0.50 Sb 2 O 4 and Co 0.50 Fe 0.50 Sb 2 O 4 were prepared by heating appropriate quantities of the dried metal oxides in evacuated sealed quartz tubes as previously described [18,20]. Fluorinated samples were obtained by heating the parent oxides in flowing fluorine gas (10% in nitrogen) at 230C and purging with gaseous nitrogen or argon [3].…”

“…The magnetic properties deduced from neutron diffraction, magnetic susceptibility and Mössbauer spectroscopy measurements in the series of composition Fe 1 − x Co x Sb 2 O 4 suggested the existence of some short range correlations within the chains [18,19] whilst in materials of formulation Fe 1 Fig. 1 The structure of FeSb 2 O 4 : FeO 6 octahedra are shaded with Fe 2+ ions located within the octahedra; O 2− ions are shown as black spheres and Sb 3+ ions are shown as white spheres − x Mg x Sb 2 O 4 , the decrease in magnetic ordering temperature with increasing concentrations of magnesium was associated with non-magnetic Mg 2+ ions weakening the magnetic interactions between Fe 2+ ions [19,20]. We have also demonstrated the capacity of these materials to accommodate additional oxygen within their structures [21].…”