Field-controlled magnetic phase separation in(La0.25Pr0.75)0.7Ca0.3Mn18O3probed by55MnNMR

Abstract

The influence of the ${}^{16}\mathrm{O}{\ensuremath{-}}^{18}\mathrm{O}$ isotope substitutions on magnetic state of perovskite-type manganite $({\mathrm{La}}_{0.25}{\mathrm{Pr}}_{0.75}{)}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ is studied by ${}^{55}\mathrm{Mn}$ NMR. Successive cycling with an isochronal exposure at different magnetic fields up to $H=8T$ is used to study the field-induced transition from antiferromagnetic insulating (AFI) state to the ferromagnetic metal (FMM) one in the ${}^{18}\mathrm{O}$-enriched sample. After exposure at $Hg{H}_{\mathrm{cr}}\ensuremath{\sim}5.3T$ the NMR spectrum of the ${}^{18}\mathrm{O}$ sample provides evidence for a magnetic phase separation (PS) into the coexisting AFI and FMM domains. Further increase of exposing field leads to a progressive growth of the FMM phase at the expense of AFI domains. Its relative fraction can be controlled by external magnetic field and the resulting magnetic structure in the PS region is discussed. Anomalous T dependence of the ${}^{55}\mathrm{Mn}$ nuclear spin-lattice relaxation rate is revealed in the FMM state of both ${}^{16}\mathrm{O}$- and ${}^{18}\mathrm{O}$-enriched samples. The possible influence of the Pr magnetic ordering at $T\ensuremath{\sim}40\mathrm{K}$ on the spin-lattice relaxation is considered.