Critical behavior and magnetocaloric effect in La_0.67Sr_0.33MnO_3.01 compounds

The polycrystalline La_0.67Sr_0.33MnO_3.01 sample was synthesized by standard solid state technique. Crystal structure of sample belongs to rhombohedral system with space group R3−c. The parameters are a = 0.55003(2) and c = 1.33753(4) nm for indexing in hexagonal system and a′ = 0.54689 nm and α = 60.38° for indexing in rhombohedral system. In order to obviously reveal the magnetic interaction we study the critical behavior by the modified Arrott plot, the Kouvel-Fisher method and the critical isotherm technique. Three main critical exponents, β, γ and δ, are derived from different three methods mentioned above. The three critical exponents obey the Widom relation and are able to collapse the different isothermal magnetization data into two branches below and above T_C based on the single scaling equation M(H, ε) = ε^βf_±(H/ε^β+γ). The critical exponents, β and γ, are on the verge of the theoretical prediction of a mean-field model, implying the existence of long-range magnetic interaction with magnetic exchange distance decaying as J(r) ≈ r^−4.57. The exponent n in the power relation ΔS_m∝Hⁿ dependence of temperature increases with temperature decreasing and approaches to 1 well below T_C and increases with temperature increasing and approaches to 2 well above T_C. Near T_C the n = 0.669 is very close to 2/3. These data support that the magnetic interaction can assign to mean-field model. The RCP increases with applied magnetic field and is about 40 J/kg under 1.2 T applied field.