Nuclear-magnetic-resonance study of the magnetically ordered manganite ${\mathrm{La}}_{1-x}{\mathrm{Pb}}_x{\mathrm{Mn}}_{1-y}{\mathrm{Fe}}_y{\mathrm{O}}_3$

A study of the manganite, ${\mathrm{La}}_{1-x}{\mathrm{Pb}}_x{\mathrm{Mn}}_{1-y}{\mathrm{Fe}}_y{\mathrm{O}}_3$, where $0.25<x<\mathrm{}0.45\mathrm{}$ and $0.0\le y\le 0.17$, has been made using the pulsed nuclear-magnetic-resonance technique over the temperature range from 1.6 to 77 K. Multiple spin echoes have been observed for ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$ nuclei in the ferromagnet ${\mathrm{La}}_{1-x}{\mathrm{Pb}}_x\mathrm{Mn}{\mathrm{O}}_3$; their number is consistent with refocusing by the quadrupole interaction. The NMR spectra have broad linewidths; experiments with a magnetic field applied indicate that nuclei both within domain walls, and within the domain bulk, contribute significantly to the absorption. The resonance frequency, defined by the signal maximum, is proportional to the average spin $〈S〉$, which in turn is a function of composition, as well as temperature. The spin-spin relaxation time $T_2$ is a minimum at the resonance frequency when $T=4.2\mathrm{}$ K; the Suhl-Nakamura interaction is suggested to be the predominant mechanism acting. The spin-echo amplitude is an oscillatory function of the time between the two exciting pulses; from these data the quadrupole splitting ($\frac{e^{2}qQ}{h}$) is deduced to be about 0.17 MHz. When some of the manganese is replaced by iron, two additional peaks, one on the low- and the other on the high-frequency side, appear in the NMR spectra, and are attributed to localized ${\mathrm{Mn}}^{4+}$ and ${\mathrm{Mn}}^{3+}$ ions, respectively. The implications of increased electron localization at the manganese ions for the magnetization of ${\mathrm{La}}_{1-x}{\mathrm{Pb}}_x{\mathrm{Mn}}_{1-y}{\mathrm{Fe}}_y{\mathrm{O}}_3$ are discussed.