Browsing by Author "Wilson, KF"

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    An AC susceptibility study of strontium cobaltates, Ln1-xSrxCoO3-δ where Ln = Y, Ho and Dy
    (Australian Institute of Physics, 2003-02-04) Wilson, KF; Goossens, DJ; Cochrane, JM; James, M
    We discuss the AC susceptibility of members of the Ln1-xSrxCoO3-δ family of materials where 0.66 ≤ x ≤ 0.9 and Ln = Y, Dy and Ho. The materials exhibit ferro- or ferrimagnetic ordering below room temperature. Despite the disorder introduced by mixed Co valence states, no glassiness is apparent in the imaginary part of the AC susceptibility or in the frequency dependence of the transition temperature. In addition, in the Dy and Ho materials it is found that the rare earth moments do not couple to the Co magnetic lattice.
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    Magnetic properties of Dy 1-x Sr x CoO 3-δ (x = 0.67 to 0.95)
    (Australian Institute of Physics, 2021-02-04) Goossens, DJ; Wilson, KF; James, M
    The AC magnetic susceptibility of Dy1-xSrxCoO3-δ has been measured from 17 to 320 K for a range of samples, x = 0.67 to 0.95. These results have shown that for x = 0.95 the systems enters a spinglass state at approximately 131K on cooling. This is demonstrated by a large cusp in the imaginary susceptibility, indicating the onset of time-dependent effects. For smaller x, the system enters a magnetically ordered state at approximately 300K. This state shows evidence for a spin state transition in the Co ions at around 120K [1], but no evidence of a spin-glass phase. Structurally, the system is tetragonal, I4/mmm, becoming closer to cubic as x increases, until at x = 0.95 the system is metrically cubic. Further, as x increases the fraction of Co4+ in the system also increases, as shown by TGA. At x = 0.95 over 50% of the Co sites are 4+, and the mixture of exchange interactions resulting is thought to give rise to the spinglass state. At smaller x the system appears weakly ferromagnetic, probably due to local ferromagnetic clusters [2], with the Dy moments remaining paramagnetic to temperatures below the instrumental limit.
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    Magnetic properties of Gd 1-x Sr x CoO 3-δ (x = 067, 090 and 095)
    (Australian Institute of Physics, 2005-01-31) Wilson, KF; Goossens, DJ; James, M
    Lanthanide cobaltates (Ln1-xSrxCoO3-δ) (Ln = lanthanide ion) with perovskite-derived structures are of potential use in solid oxide fuel cells [1-4] and oxygen separation [5-6]. The materials show magnetic glassiness [7-8] and ferromagnetism [9]. La1-xSrxCoO3-δ has been widely studied [10 for example]. Interest has recently increased in phases with the smaller lanthanide ions such as Ho, Y and Dy [11]. This work adds to a systematic exploration of the structure and magnetic properties of this family of materials. The physical properties of these materials depend on composition (Ln3+/Sr2+, O/vacancy, Co3+/Co4+). Oxygen ionic conductivity changes with the O/vacancy ordering and associated structural relaxation [3]; magnetic behaviour will be affected by the Co3+/Co4+ ratio and distribution.