Coexistence of short- and long-range ferromagnetic order in La0.7Sr0.3Mn1−xCoxO3 compounds

Abstract

Polycrystalline La0.7Sr0.3Mn1−xCoxO3 (x = 0.0–1.0) samples were synthesized by solid-state reaction. Structural and magnetization studies reveal the replacement of Co for Mn in La0.7Sr0.3Mn1−xCoxO3, and the decrease of the Curie temperature (TC) from 360 K (for x = 0) to 224 K (for x = 1). Positive slopes observed in the H/M versus M2 curves prove all the samples undergo a second-order magnetic phase transition. By analysis of the M(H) data at temperatures around TC using the Kouvel-Fisher method, we obtained the values of critical parameters (TC, β, γ, and δ). The results suggest an existence of short-range FM order in the sample x = 0 with β = 0.377. Meanwhile, for the case of Co-doped samples, their β values in the range of 0.403–0.457 indicate a coexistence of short and long-range FM order. This means that Co-doping favors establishing FM long-range order in La0.7Sr0.3Mn1−xCoxO3. From M(H) data, we have also determined the magnetic entropy change (ΔSm) for the samples. We have found that the ΔSm(T) curves for different applied fields are collapsed onto a universal curve by normalizing the ΔSm(T) curves to their respective maximum value ΔSmax (i.e., ΔSm(T)/ΔSmax) and rescaling the temperature axis above and below TC with θ=(T−TC)/(Tr−TC), where Tr is the reference temperature.