An NMR study of Pr0.5Ca0.5Mn1-xGaxO3 (X=0 and 0.03)

An NMR study of polycrystalline Pr(0.5)Ca(0.5)Mn(1-x)GaxO(3) (x = 0 and 0.03) at 3 K is presented. Zero field spin-echo spectra of the Ga doped compound consist of an overlapping Ga-69,Ga-71 signal at 74 MHz (hyperfine field of 5.3 T), a Mn-55 double exchange line at 375 MHz (35.5 T) and a weak Mn3+ signal between 400 and 550 MHz. Measurements in an applied field show a step-like increase in the double exchange line intensity, which corresponds to an increase in the amount of the ferromagnetic metallic phase. This coincides with a step-like feature in the bulk magnetization measurements. The effect is similar to that in the previous field dependent Mn-55 NMR measurements of Pr0.67Ca0.33MnO3. At the demagnetized and remanent state, a variation of spin-spin relaxation time, T-2, across the Mn-55 line, due to the Suhl-Nakamura interaction is observed, which suggests that the ferromagnetic metallic double exchange regions, at liquid helium temperatures, are at least 4 nm in size.