Continuously varying of critical exponents with the bismuth doped in the La0.8Na0.2Mn1-xBixO3 (0 ≤ x ≤ 0.06) manganites

• Published in: Journal of magnetism and magnetic materials 2018-04, Vol.451, p.629-638
• Main Authors: Laouyenne, M.R., Baazaoui, M., Mahjoub, Sa, Cheikhrouhou-Koubaa, W., Farah, Kh, Oumezzine, M.
• Format: Article
• Language: English
• Subjects: Critical behavior; Landau theory; Second order phase transition
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2017.11.123

•The compounds exhibit a second order phase transition.•The critical exponent values lie between the Tricritical mean filed, 3D-Ising and Heisenberg models.•The Landau theory is used to estimate the magnetic entropy change. A comprehensive analysis of the critical phenomena for the nominal compositions La0.8Na0.2Mn1-xBixO3 (0 ≤ x ≤ 0.06) was carried out. The critical exponents values were calculated by various techniques such as Modified Arrott plot (MAP), Kouvel Fisher (KF) method and critical isotherm (CI). Comparison of the experimental data with the above theoretical models showed that the critical exponents β, γ and δ for the undoped sample are quite well described by the tricritical mean-field model (TMF). Furthermore, the substitution of Mn by Bi ions led to the increase of γ which approached the 3D-Heisenberg model (γ = 1 325 and β took similar values to those predicted by the TMF model. The validity of the exponents values was confirmed with the scaling hypothesis; the M (T, ε) curves collapse onto two independent universal branches below and above Tc.