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

Magnetic susceptibility, χ ( T ) , is investigated in ceramic La 1− x Ba x MnO 3 (LBMO) with x = 0.02 – 0.25 in the range of fields B = 10 – 80 G and temperatures T = 5 – 310 K . All samples exhibit a paramagnetic (PM) to ferromagnetic (FM) transition with T C increasing with x from 177 K ( x = 0.02 ) to 295 K ( x = 0.25 ) and magnetic irreversibility decreasing below T C with increasing x . In the PM phase an interval of the Curie–Weiss behavior of χ ( T ) with an effective Bohr magneton number, p eff ∼ 30 – 40 , is observed above T 1 ∼ 260 – 290 K . Below T 1 and down to T cr ∼ 190 – 220 K the susceptibility follows the scaling law χ - 1 ( T ) - χ - 1 ( T C ) ∼ ( T / T C - 1 ) γ with γ = γ 1 ≈ 1.4 corresponding to a three-dimensional (3D) Heisenberg spin system. Below T cr , χ ( T ) obeys the same scaling law as for T > T cr , but with another value of γ = γ 2 ≈ 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 T 1 . The size of these particles increases between T 1 and T cr up to nanometer scale, forming critical percolation clusters below T cr . The magnetic irreversibility is connected to a mixed, FM and cluster-glass, phase.