Influence of the phase separation effect on low-field magnetic properties of La1−xBaxMnO3

Magnetic susceptibility, χ(T), is investigated in ceramic La1−xBaxMnO3 (LBMO) with x=0.02-0.25 in the range of fields B=10-80G and temperatures T=5-310K. All samples exhibit a paramagnetic (PM) to ferromagnetic (FM) transition with TC increasing with x from 177 K (x=0.02) to 295 K (x=0.25) and magnetic irreversibility decreasing below TC with increasing x. In the PM phase an interval of the Curie-Weiss behavior of χ(T) with an effective Bohr magneton number, peff∼30-40, is observed above T1∼260-290K. Below T1 and down to Tcr∼190-220K the susceptibility follows the scaling law χ-1(T)-χ-1(TC)∼(T/TC-1)γ with γ=γ1≈1.4 corresponding to a three-dimensional (3D) Heisenberg spin system. Below Tcr, χ(T) obeys the same scaling law as for T>Tcr, but with another value of γ=γ2≈1.7-1.8, characteristic of a 3D percolation system. The temperature dependence of the susceptibility observed in the PM phase is explained by small FM particles embedded in the host LBMO matrix above T1. The size of these particles increases between T1 and Tcr up to nanometer scale, forming critical percolation clusters below Tcr. The magnetic irreversibility is connected to a mixed, FM and cluster-glass, phase.