Nanometric size effect on magnetic ordering in half-doped La_0.5Ca_0.5MnO₃ manganite: EPR probing

Measurements of the X-band electron paramagnetic resonance and the model fittings of the linewidth and intensity versus temperature dependences were employed to probe the finite-size effect on the magnetic ordering in half-doped La_0.5Ca_0.5MnO₃ manganite. It is shown that complex mixed magnetic ordering in bulk samples, comprised of the antiferromagnetic and the charge-ordered (AFM/CO) component, together with the ferromagnetic one, appear to be unstable regarding this effect; the AFM/CO phase is suppressed in nano-samples, which agrees with the data of magnetic measurements. In addition, we have managed to show that the FM state, appearing in nano-grains, is frustrated due to (i) an AFM-like core-shell interaction and (ii) a strong spin disorder at the surfaces and core-shell transition layers.