Syntheses and Magnetic-Properties of Zn-Diluted Sr-Based Perovskite Cobalt Oxides, Sr1−x Zn x CoO3; 0.05≤x≤0.3

Abstract

In order to check the solubility of Zn in the (Sr1−x Zn x )CoO3 perovskite structure and their research findings, several polycrystalline samples have been prepared under wide extreme synthesis conditions at 6 GPa/1300–1650 °C. While 0.05≤x≤0.3 compositions revealed single phased cubic structure materials, x>0.3 showed multi-phased materials for (Sr1−x Zn x )CoO3 system. Like other substituted perovskite cobalt oxide systems (Ca, Y, Ho and Ce), the transport properties of the present materials show rather sizable changes with respect to ‘x’, although there are insignificant variations in lattice parameter and in Curie temperature, T c . All the present samples show soft ferromagnetism with T c in the range of 272–285 K for 0.05≤x≤0.3. The effective paramagnetic moment, P eff determined from the paramagnetic region decreases upon the substitution of Zn for Sr-site. These P eff (3.3–2.8 μB/Co) values for 0.05≤x≤0.3 compositions seem to suggest that the Co4+ lie in intermediate spin (IS) state for the present (Sr1−x Zn x )CoO3 series, although they are slightly smaller than those expected for IS-Co4+; P eff=3.87 μB/Co. The electrical resistivity is found to increase with increase of ‘x’ for the investigated samples. The temperature and field dependence of both positive and negative magnetoresistance (MR) are noted for the Zn substituted samples. About 5% of –MR is observed for x=0.05 sample around the transition temperature (280 K) under the field strength difference, ΔH=90 kOe. The present research findings are compared with our previous results on different perovskite cobalt oxides.