An NMR Study of Pr 0.5 Ca 0.5 Mn 1-x Ga x O 3 (x=0 and 0.03)

C.J. Oates a , Cz. Kapusta a,b , P.C. Riedi b , M. Sikora a , D. Zając a , D. Rybicki a , C. Martin c , C. Yaicle c and A. Maignan c a Department of Solid State Physics, Faculty of Physics and Nuclear Techniques, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Cracow, Poland b School of Physics and Astronomy, University of St. Andrews, St. Andrews, KY16 9SS, Scotland, United Kingdom c Laboratoire CRISMAT --- UMR 6508, ISMRA et Universite de Caen, 6 Boulevard du Marechal JUIN, 14050 Caen Cedex, France

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An NMR study of polycrystalline Pr 0.5 Ca 0.5 Mn 1- x Ga x O 3 (x=0 and 0.03) at 3K is presented. Zero field spin-echo spectra of the Ga doped compound consist of an overlapping 69,71 Ga signal at 74MHz (hyperfine field of 5.3T), a 55 Mn double exchange line at 375MHz (35.5T) and a weak Mn 3+ signal between 400 and 550MHz. 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 55 Mn NMR measurements of Pr 0.67 Ca 0.33 MnO 3 . At the demagnetized and remanent state, a variation of spin-spin relaxation time, T 2 , across the 55 Mn 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 4nm in size.

DOI: 10.12693/APhysPolA.105.189 PACS numbers: 76.60.--k, 75.47.Gk