Reply to “Comment on ‘NMR in manganese perovskites: Detection of spatially varying electron states in domain walls’ ”

Abstract

In their Comment Savosta and Novák claim that the doubly peaked 55 Mn NMR line shape observed in La 0.67 Ca 0.33 MnO 3 for TϽ70 K ͓Phys. Rev. B 58, 12 237 ͑1998͔͒ is not real, but an artifact resulting from the experimental conditions. In support to their arguments, they present 55 Mn line-shape measurements at 77 K. In this reply we present 55 Mn NMR line-shape measurements under the experimental requirements suggested by Savosta and Novák, and show that at low temperatures the line shape still consists of two distinct peaks with different rf enhancement factors. This effect is explained in view of recent experimental results.In a recent paper 1 we have shown that at low temperatures the 55 Mn NMR spectra of La 0.67 Ca 0.33 MnO 3 , obtained with a two-pulse spin-echo technique, are doubly peaked with peaks at frequencies 380 MHz and 395 MHz. This effect has been attributed to the lower charge carrier density in domain walls in comparison to the charge carrier density in ferromagnetic ͑FM͒ domains. For TϾ70 K, the double peak was no more observed, and spectra were found to consist of a broad single peaked Gaussian line shape.In their Comment, Savosta and Novák claim that the double peak is due to the short spin-spin relaxation time T 2 value at the center of the line shape, which distorts the central part of the signal. They claim that by using very short interpulse time intervals , such that ӶT 2 , the double peak will disappear and the true single Gaussian line shape will be restored.In order to clarify the question raised by them we performed low-temperature 55 Mn NMR line-shape measurements on La 0.67 Ca 0.33 MnO 3 , after setting ϭ3 sec, which in all measurements fulfilled the condition ӶT 2 . Figure 1͑a͒ exhibits line-shape measurements at Tϭ3.2 K, and at four different radio frequency ͑rf͒ power levels. It is clearly observed that by decreasing rf power the low-frequency part of the signal decreases rapidly, whereas the high-frequency part remains almost unchanged. This unambiguously shows that the signal consists of two components, which respond differently to the power level of the rf excitation pulse, i.e., they have different rf enhancement factor. 3 On the contrary, at 77 K ͓Fig. 1͑b͔͒ the line shape remains unchanged and only the signal intensity reduces drastically by decreasing rf power level, which implies a uniform rf enhancement across the whole spectum. The possibility that at Tϭ3.2 K the doubly peaked line shape is produced by an extremely short T 2 FIG. 1. ͑a͒ 55 Mn NMR line-shape measurements of La 0.67 Ca 0.33 MnO 3 at 3.2 K, and different rf power levels. ͑b͒ The same experiment at 77 K. FIG. 2. 55 Mn T 2 as a function of temperature measured at rf power level Ϫ5 dB ͑filled circles͒. For reasons of comparison T 2 from Ref. 1 ͑gray circles͒ is also presented.

The Nd–Mn exchange interaction in Nd0.7Sr0.3MnO3

“…If the lineshape does change with power of the applied field then it is likely that the two peaks have different rf enhancement factors [11]. If this is the case, since rf enhancement is produced by the coherent oscillation of electron spins, then it is possible that the two DEX peaks originate from spatially resolved ferromagnetic regions (possibly with different electronic properties), as was seen in La 0.67 Ca 0.33 MnO 3 [12]. However, such a possibility can be eliminated for Nd 0.7 Sr 0.3 MnO 3 , since figure 6 suggests that both peaks have similar rf enhancement factors.…”