Low-field magnetic properties of La1−xSrxMn1−yFeyO3

Abstract

Low-field (B = 10 G – 1 kG) magnetic properties are investigated in ceramic samples of La1–xSrxMn1−yFeyO3 (LSMFO) with x = 0.3 and y = 0.15, 0.20 and 0.25. A substantial decrease of the ferromagnetic (FM) Curie temperature, TC, with increasing y is observed, which is connected to breaking of the FM double-exchange interactions by doping with Fe. Strong magnetic irreversibility at B = 10 G gives evidence for a frustrated magnetic state of LSMFO. The asymptotic Curie-Weiss behaviour of the magnetic susceptibility, χ (T), observed well above TC, yields the values of the effective Bohr magneton per magnetic ion, exceeding considerably those of single ions. Critical behaviour of χ (T) ∼ (T/TC – 1) −γ is influenced at y = 0.15 and 0.20 by a percolative (γ ≈ 1.8) and non-percolative or Heisenberg (γ ≈ 1.4) spin systems. At y = 0.25 the percolative contribution to χ (T) is not observed. The low-field magnetic properties above can be explained by the phase separation effect or generation of nanosize FM particles in the paramagnetic host matrix of LSMFO.