Size and Nonstoichiometry Effects on Magnetic Properties of ${\hbox {La}}_{0.5}\hbox {Ca}_{0.5}\hbox {MnO}_{3}$ Manganite

AC and dc magnetic measurements in temperature interval 5-350 K and at external magnetic field H les 5 T were employed to probe the finite-size and nonstoichiometry effects on magnetic ordering of La_0.5Ca_0.5MnO₃ half-doped manganite compound. It is shown that the complex mixed magnetic ordering in bulk samples appears to be unstable regarding the both effects. The strongest one is the size effect, suppressing the mixed order and inducing the ferromagnetic-like one, which is characteristic also for other half-doped manganites. The small variations in cation composition (nonstoichiometry), which don´t influence the crystal structure, lead to strong perturbations in the mixed magnetic ordering of the bulk. The results obtained are discussed in the terms of pronounced competition of spin, charge and lattice degrees of freedom, characteristic for doped manganites.