Magnetic Phase Separation in ${\mathrm{L}\mathrm{a}}_{1-x}{\mathrm{S}\mathrm{r}}_x\mathrm{C}\mathrm{o}{\mathrm{O}}_3$ by ${}^{59}\mathrm{C}\mathrm{o}$ Nuclear Magnetic Resonance

${}^{59}\mathrm{C}\mathrm{o}$ NMR measurements on ${\mathrm{L}\mathrm{a}}_{1-x}{\mathrm{S}\mathrm{r}}_x\mathrm{C}\mathrm{o}{\mathrm{O}}_3$ reported here establish unequivocally, for the first time, the coexistence of ferromagnetic regions, spin-glass regions, and hole-poor low spin regions at all $x$ values from 0.1 to 0.5. A zero external field NMR spectrum, which is assigned to the ferromagnetic regions, has a spectral shape that is nearly $x$ independent at 1.9 K, as are the relaxation times, $T_1$ and $T_2$. The integrated spectral area increases rapidly with $x$ up to $x=0.2$ and then decreases slightly for larger $x$. In a field of 9.97 T, a narrow NMR line is observed at 102 MHz, identical to that found in $x=0$ samples in previous work. The integrated intensity of this spectrum decreases rapidly with increasing $x$, and is ascribed to hole-poor low spin regions. Beneath this spectrum, a third broad line, with a peak at 100 MHz, is assigned to a spin- or cluster-glass-like phase.

Figure 1

Zero field ${}^{59}\mathrm{C}\mathrm{o}$ FNMR spectrum for ${\mathrm{L}\mathrm{a}}_{1-x}{\mathrm{S}\mathrm{r}}_x\mathrm{C}\mathrm{o}{\mathrm{O}}_{\mathrm{3}}$ for $x=0.1$, 0.18, 0.2, and 0.4. (Inset) Four Gaussian fit of the $x=0.3$ spectrum. The peaks are at 206, 198, 172, and 142 MHz. The peak positions are independent of $x$, but the weight of the low frequency peak increases with $x$ at the expense of the two high frequency peaks.

Figure 2

${}^{59}\mathrm{C}\mathrm{o}$ NMR spectra in a field of $B=9.97\mathrm{T}$ for Sr concentrations $x$ in the range 0.1 to 0.4. The fitted Gaussian curves for $x=0.1$ (inset) are centered at 100 MHz and 102 MHz, respectively. The baselines are offset for clarity.

Figure 3

The total integrated area of the zero field spectra and the narrow, 102 MHz Gaussian LS 9.97T NMR spectra as a function of $x$, showing the coexistence of the FM and non-FM regions over the entire range of composition.