Effect of substitution of magnetic rare earths for La on the structure, electric transport and magnetic properties of La2SrFe2O7

Study of Structural, Electrical, and Magnetic Properties of Layered Perovskite Oxides LnSr2TiFeO7 (Ln = Nd, Gd)

“…The results suggest that the electrical resistivity decreases with decreasing ionic size of the rare earth, which could be attributed to enhancement of the three-dimensional (3D) character along the c-axis because of the proximity of the (Ti/Fe)O 2 and (Ln,Sr)O layers along the c-axis as a result of the decrease in lanthanide ionic size. A similar type of results was also reported by Sharma et al 17 Various equations based upon different mechanisms of conduction, such as those applicable in case of the Arrhenius model, polaron hopping model, and variable-range hopping (VRH) model, were applied to the data of electrical resistivity of the phases. We found that the conduction process in the phases is best described using the Mott VRH model.…”

“…The data in Tables I and II suggest that the unit cell parameters a and c of the Gd-phase are smaller than the phase containing Nd, which is consistent with the decrease in the lanthanide ionic radius. 17,21 Analysis of the cell parameters shows that the total decrease in the c parameter from the Nd to Gd compound is much larger than the decrease in the a parameter. This could be attributed to the cumulative effect of reduced lanthanide radii along the c direction where the layers are stacked.…”

“…The corresponding smaller rate of decrease of a is attributed to the strong nature of Ti/Fe-O bond in the xy plane, which makes a difficult to change. 17 The temperature dependence of electrical resistivity of the sintered pellets (density given in Table III) of the phases is given in Fig. 3, where resistivity (q) is plotted against temperature (T).…”

“…12,13 The phases Ln 2 SrFe 2 O 7 (Ln = Nd, Gd, and Dy) crystallize with a tetragonal unit cell in space group I4/ mmm and are electrical insulators. 17 Magnetic studies suggest that the Weiss constant (h) increases with substitution of the rare earths in the order Dy > Gd > Nd. Although many studies of the Ruddlesden-Popper phase (n = 2) containing lanthanum ion with composition (La,Sr) 3 Fe 2 O 7 are reported in the literature, there are hardly any reports on this phase containing other rare-earth ions and with partial substitution of Fe by Ti.…”

The solid solution Sr3Ti2-xFexO7-δ (x ≤ 0.5): characterization of Fe (III) – Fe (IV) mixed valences

“…Exchange interactions between Fe 3+ cations in the layered perovskite like phases are antiferromagnetic [23,24]. When atoms with different electronic configuration are concerned, the exchange interactions are always ferromagnetic.…”