Magnetic properties and phase separation in Pr$_{1-x}$Sr$_{x}$CoO$_{3}$, using $^{59}$Co NMR

Doped transition metal oxides including manganites and cobaltites have revealed a rich variety of properties that may be technologically important. The mixed valence cobaltite Pr$_{1-x}$Sr$_{x}$CoO$_{3 }$(PSCO) has a phase diagram reminiscent of La$_{1-x}$Sr$_{x}$CoO$_{3 }$(LSCO) but with a number of significant differences. For x=0.5 the system is ferromagnetic (FM) below $T_{C}$= 240 K but anomalous magnetization behavior is found close to 120 K with an associated crystal structure change from low symmetry to tetragonal with decreasing $T$. For x $<$ 0.3 no change in magnetic properties or crystal structure is found below $T_{C}$. Zero-field $^{59}$Co NMR spectra show that differences in FM character between x=0.5 and x=0.3 samples are negligibly small at temperatures in the range 3-30 K No FM line was observed for x=0.2; a narrow paramagnetic- like signal only slightly shifted from the diamagnetic $^{59}$Co spectrum is observed in high- field NMR for all three x values, providing evidence of some form of phase separation where a paramagnetic phase coexists with the FM phase. The results will be compared with the very different phase separation data previously obtained for LSCO.