NMR study of La1-xSrxMnO3 compounds
|Czesław Kapusta 2, Dariusz A. Zajac 2, Peter C. Riedi 3, Damian Rybicki 2, Marcin Sikora 2, Colin J. Oates 2, Jose M. De Teresa 1, Clara Marquina 1, Ricardo M. Ibarra 1|
1. Universidad de Zaragoza-CSIC, Facultad de Ciencias, Pedro Cerbuna 12, Zaragoza 50009, Spain
We report on the nuclear magnetic resonance (NMR) study of "colossal magnetoresistive" manganites La1-xSrxMnO3. The temperature measurement of zero field 55Mn and 139La spin-echo spectra were carried out on samples with doping x=0.125 and 0.15. Previous works on these compounds suggest that the ground state of both compounds is a ferromagnetic conductor below TC and orbitally ordered ferromagnetic insulator below TOO < TC. Neutron diffraction, magnetization, resistivity and linear thermal expansion measurements on our polycrystalline samples indicate TC around 205 K and 240 K, for x=0.125 and x=0.15, respectively. The temperature of orbital ordering, TOO, is 150 K and 180 K for x=0.125 and x=0.15, respectively. The 55Mn spectra of both compounds exhibits Mn3+ and Mn4+ as well as double exchange (DE) lines with different relative intensities. The DE line corresponds to ferromagnetic metallic clusters (FMM) and the Mn3+ and Mn4+ lines are due to charge localised (CL) ferromagnetic insulating (FMI) regions. The DE line for x=0.125 is observed up to temperatures around or slightly above bulk TC, revealing the presence of long lived FMM clusters. The intensity of the Mn4+ line decreases strongly with increasing temperature and the signal is not observed above 150 K due to the melting of FMI regions. The 139La spectra of both compounds at 4.2K exhibit two lines, which are attributed to FMM and FMI regions and the ratio of their intensities is similar to that of the respective FMM and FMI signals in the 55Mn spectra. This ratio shows that there are fewer FMM clusters in x=0.125 than in x=0.15. Measurements on the 55Mn DE line at 4.2 K, for different pulse spacing, shows no effect of the Suhl-Nakamura interaction for x=0.125, in contrast to x=0.15. This feature indicates that the FMM clusters for x=0.125 are of nanometer size, whereas for x=0.15 they are much larger.
Presentation: oral at E-MRS Fall Meeting 2003, Symposium B, by Czesław Kapusta
See On-line Journal of E-MRS Fall Meeting 2003
Submitted: 2003-05-27 18:23 Revised: 2009-06-08 12:55