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−δ(0≤y  ≤0.3) [LSMZO] perovskite of rhombohedral symmetry (space group: R3¯c) with yy up to 30 at.% could be synthesized notwithstanding the differences in ionic radii of MnV I3+ (i.r.=0.645 Å) and ZnV I2+ (i.r.=0.74 Å). 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>8at.% leading to PMI even at low temperatures, measured up to 8 K (presently). The FM to PM transition (Tc)(Tc) and the peak (Tp)(Tp) in resistivity–temperature curves decreases with the Zn-content. The charge-transport in pp-type LSMZO is predictable by variable range hopping (VRH), which changes to nearest-neighbor hopping of small polarons (NNHP) at T>TpT>Tp. Non-stoichiometry (0.005≤δ≤0.21)(0.005≤δ≤0.21) evaluated chemically from redox titrations indicated the prevalence of excess oxygen vacancy (VO) rather than charge compensatively predictable values which, in turn, indicates the diminishing Mn4+ content in LSMZO. The VO’s act as electron donors in pp-LSMZO and this increases the resistivity (ρRT)(ρRT) associated with the shift in TcTc to low temperatures. Increased ρRTρRT on annealing in low po2 is a clear evidence on the role of VO in LSMZO.