La139NMR investigation of spin ordering inLa0.5Ca0.5MnO3

Abstract

${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ NMR in a zero external magnetic field has been used as a probe in order to study the Mn spin ordering of ${\mathrm{La}}_{0.5}$ ${\mathrm{Ca}}_{0.5}$ ${\mathrm{MnO}}_3$. For T<${\mathrm{T}}_{\mathrm{c}}$ two different spin configurations are detected, assigned to a ferromagnetic and an antiferromagnetic one, which persist down to the lowest measured temperature T=90nK. Close to ${\mathrm{T}}_{\mathrm{c}}$ strong coherent spin fluctuations are detected that presumably drive the paramagnetic-to-ferromagnetic phase transition. Complementary magnetic and ${\mathrm{Mn}}^{4+}$ electron paramagnetic resonance measurements are in agreement with the NMR results.