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: R 3 ¯ c ) with y 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 > 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 ≤ δ ≤ 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 ( ρ R T ) associated with the shift in T c to low temperatures. Increased ρ R T on annealing in low p o 2 is a clear evidence on the role of V O in LSMZO.