Thermodynamics of Paramagnetic-Ferromagnetic Phase Transition in ${\rm La}_{0.7}{\rm Ca}_{0.3}{\rm MnO}_{3}$ Manganite: “Griffiths singularity” versus Chemical Disorder and Lattice Effects

Magnetic and electron paramagnetic resonance measurements were employed to probe magnetic interactions in the single crystal and ceramic of La
_0.7
Ca
_0.3
MnO
₃
manganite in the vicinity and above their paramagnetic-ferromagnetic phase transition. It is shown that strong differences in the Curie point values and in the temperature dependences of inverse susceptibilities are observed in spite of the same structure and cation composition of both samples. We suggest that the difference between lattice effects in these samples, induced by their different chemical disorder, proves a more realistic description of experimental data than so-called "Griffiths singularity".