Unconventional critical behavior in a Sm-based ferromagnetic manganite : Effect of tricritical point

Abstract

We have studied the critical phenomena in a single crystal of a ferromagnetic manganite (Sm1-xNdx)0.52Sr0.48 MnO3 with x = 0.6, which is in the vicinity of a tricritical point (x∗ ≈ 0.4), separating first-(x <0.4) from second-order (x >0.4) phase transition. Through magnetization scaling analysis, we have determined the critical exponents (β = 0.23 ± 0.01, γ = 1.30 ± 0.01, and δ = 6.63 ± 0.03) and critical amplitudes, which are also in accordance with the results obtained from the magnetic field dependence of magnetic entropy change. The exponents obey the scaling laws but they do not belong to any existing universality class - a clear violation of universality hypothesis. The occurrence of such unusual critical behavior has qualitatively been explained through mean-field theory, which reveals that for a system in the vicinity of tricritical point, the critical exponents may substantially differ from conventional universality.