Impact of a small amount of vacancy in both lanthanum and calcium on the physical properties of nanocrystalline La0.7Ca0.3MnO3 manganite

• SEM images reveal a spherical shape with an average grain size lower than 100 nm.
• Curie temperature TC increases with lacuna.
• (1/χ) versus temperature indicates Griffiths phase occurrence.
• β and γ exponents obey to the tricritical mean-field theory model.

In this paper, we report the effect of both lanthanum and calcium (1%) on the structural and magnetic properties of nanocrystalline La0.7Ca0.3MnO3 manganite. Our powder specimens were synthesized using the sol–gel method with an annealing temperature of 850 °C. The X-ray diffraction patterns refined using Rietveld method confirms that our compounds are single phase and crystallize in the orthorhombic perovskite structure (Pbnm space group). The morphology of the samples, observed using a scanning electron microscope (SEM), reveals a spherical shape with an average grain size lower than 100 nm. Magnetization measurements versus temperature under low magnetic applied field (0.05T) show a paramagnetic–ferromagnetic transition for all compounds. The Curie temperature TC is found to increase with lacuna in both cases. In addition, the inverse of the susceptibility (1/χ) as a function of temperature indicates a deviation from the Curie Weiss lawn, signature of Griffiths phase occurrence. Experimental results for the critical β and γ exponents are typical of a behavior governed by the tricritical mean-field theory model.Using magnetization measurements as a function of magnetic applied field at several temperatures, we have deduced the magnetic entropy change, which undergoes an enlargement for both lacuna sites. The obtained results are compared to calculated ones based on the Landau theory and a good concordance is observed.

(a) Spontaneous magnetization and inverse of susceptibility versus T for La0.7Ca0.29□0.01MnO3 compound. Inset the Ln–Ln plot used to determine the critical exponents β and γ. (b) M vs μ0H isotherm measured at TC = 200 K. Inset the Ln–Ln plot for the critical exponent δ calculation as well as the modified Arrott plot for La0.7Ca0.29□0.01MnO3 compound.Figure optionsDownload as PowerPoint slide