Modification of the ground state in Sm-Sr manganites by oxygen isotope substitution

The effect of $^{16}$O $\to$ $^{18}$O isotope substitution on electrical resistivity and magnetic susceptibility of Sm$_{1-x}$Sr$_x$MnO$_3$ manganites is analyzed. It is shown that the oxygen isotope substitution drastically affects the phase diagram at the crossover region between the ferromagnetic metal state and that of antiferromagnetic insulator (0.4 $< x <$ 0.6), and induces the metal-insulator transition at for $x$ = 0.475 and 0.5. The nature of antiferromagnetic insulator phase is discussed.Comment: 4 pages, 3 eps figures, RevTeX, submitted to Phys. Rev. Let

Isotope effect for transport and magnetic properties of La

The effect of $^{16}{\rm O}\rightarrow ^{18}{\rm O}$ isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La0.35Pr0.35Ca0.3MnO3 epitaxial thin films deposited onto LaAlO3 and SrTiO3 substrates. For the films on LaAlO3, the isotope substitution resulted in the reversible transition from a metal-like to insulating state. The applied magnetic field ($\rm H \geq 2 T$) transformed the sample with 18O back to the metallic state. The films on SrTiO3 remained metallic at low temperatures for both 16O and 18O, but the shift of the resistivity peak corresponding to onset of metallic state exceeded 63 K after $\rm ^{16}O\rightarrow ^{18}O$ substitution. The temperature dependence of both resistivity and magnetic susceptibility was characterized by hysteresis, especially pronounced in the case of the films on LaAlO3. Such a behavior gives certain indications of the phase separation characteristic of interplay between ferromagnetism and charge ordering