Strange critical behaviors of ferromagnetic to paramagnetic transition in La0.5Ca0.5MnO3 nanowires bundles

Abstract

Highly ordered La_0.5Ca_0.5MnO₃ nanowires bundles are synthesized using mesoporous SBA-15 silica as the hard template. The magnetic properties and critical behaviors of the ferromagnetic–paramagnetic (FM–PM) phase transition of the La_0.5Ca_0.5MnO₃ nanowires bundles are investigated through isothermal magnetization methods. The calculated results show that the FM–PM transition is second order and the magnetic interaction has some deviations from the mean-field model. Though the obtained critical parameters of β = 0.596 ± 0.009, γ = 1.131 ± 0.008 and δ = 2.99 ± 0.05 follow the Widom scaling relation δ = 1 + γ/β and the single scaling equation M(H,|ε|) = ε^βf_±(H/|ε|^β+γ), the critical exponents do not obey the magnetization entropy scaling theory, indicating that the nanometer-size effect play a significant role on the magnetic phase transition and magnetic entropy for La_0.5Ca_0.5MnO₃ nanowires bundles.