Effects of Zn substitution on the magnetic and transport properties of La0.6Sr0.4Mn1-yZnyO3-δ (0 ≤ y ≤ 0.3)

Phase-singular solid solutions of La0.6Sr0.4Mn1-yZnyO3-delta (0 <= y <= 0.3) [LSMZO] perovskite of rhombohedral symmetry (space group: R (3) over barc) with y up to 30 at.% could be synthesized notwithstanding the differences in ionic radii of Mn-VI(3+) (i.r. = 0.645 angstrom) and Zn-VI(2+) (i.r. = 0.74 angstrom). The LSMZO <= 02 compositions are ferromagnetic metallic (FMM) at room temperature whereas LSMZO-02-08 are ferromagnetic insulators (FMI) and LSMZO > 08 are paramagnetic insulators (PMI). Total obliteration of the FM transition is unique to Zn-doping at y > 8 at.% leading to PMI even at low temperatures, measured up to 8 K (presently). The FM to PM transition (T-c) and the peak (T-p) in resistivity-temperature curves decreases with the Zn-content. The charge-transport in p-type LSMZO is predictable by variable range hopping (VRH), which changes to nearest-neighbor hopping of small polarons (NNHP) at T > T-p. Non-stoichiometry (0.005 <= delta <= 0.21) evaluated chemically from redox titrations indicated the prevalence of excess oxygen vacancy (V-O) rather than charge compensatively predictable values which, in turn, indicates the diminishing Mn4+ content in LSMZO. The V-o's act as electron donors in p-LSMZO and this increases the resistivity (PRT) associated with the shift in T-c to low temperatures. Increased rho(RT) on annealing in low p(o2) is a clear evidence on the role of V-O in LSMZO. (C) 2006 Elsevier Ltd. All rights reserved.