Critical behavior in Sr-doped manganites La0.6Ca0.4−xSrxMnO3

The critical behavior of La0.6Ca0.4−xSrxMnO3 (x = 0, 0.2 and 0.4) compounds has been investigated based on the data of static magnetic measurements in the vicinity of its critical temperature TC. Through various techniques such as modified Arrott plot, Kouvel–Fisher method and critical isotherm analysis, the estimated critical exponents are found to be (β = 0.267, γ = 0.992, δ = 4.896 at TC = 268.12), (β = 0.501, γ = 1.045, δ = 2.992 at TC = 344.37) and (β = 0.386, γ = 1.293, δ = 4.88 at TC = 371.02), for x = 0, 0.2 and 0.4; close to tricritical mean field, mean field and 3D-Heisenberg model values, respectively. The reliability of the critical exponents values was confirmed by the Widom scaling relation and the universal scaling hypothesis. Following the Harris criterion, we deduced that the disorder in our case is relevant, which can be the cause of the change in the universality class. Moreover, the local exponent n was studied in terms of the field dependence of the magnetic entropy change. It has been noted that n evolves with field in the entire studied temperature range for all samples. The invalidity of the mean field model for x = 0 and 0.4 contents was confirmed at the peak temperature. Far above the transition temperature, the Curie–Weiss law is well satisfied. The differences observed in the n values below the transition are mentioned. Furthermore, unlike the modified Arrott or Kouvel–Fischer methods, the performed analysis is shown to be useful to examine critical exponents and their effects in mixed phases materials.

Scaling plots indicating two universal curves below and above TC for La0.6Ca0.4MnO3 (a), La0.6Ca0.2Sr0.2MnO3 (b) and La0.6Sr0.4MnO3 (c) samples. Inset show the same plots on a log–log scale. Inset show the same plots on a log–log scale.Figure optionsDownload as PowerPoint slideHighlights
► Relevant disorder causes the universality class change for LaCa(Sr)MnO compounds.
► Invalid mean field model for x = 0 and 0.4 contents confirmed by the n(T, H) plots.
► n(T, H) plots examine the critical exponents and effects in mixed materials.