NUKLEONIKA 2004, 49(Supplement 3):s37-s42

SPIN AND LATTICE DYNAMICS OF La2/3Ca1/3MnO3 DOPED WITH 1% 119Sn

Janusz PrzewoŸnik1, Jan ¯ukrowski1, Janusz Chmist1, Ewa Japa1, Andrzej Ko³odziejczyk1, Karol Krop1, Karl Kellner2, Gerhard Gritzner2

1 Department of Solid State Physics, Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, 30 A. Mickiewicza Ave., 30-059 Kraków, Poland,
2 Institut für Chemische Technologie Anorganischer Stoffe, J. Kepler Universität Linz, A-4040 Linz, Austria

1 at.% 119Sn doped La0.67Ca0.33MnO3 compound was studied by Mössbauer spectroscopy, magnetization, AC susceptibility and resistivity measurements. Huge separation (66 K) of the transition temperatures from the ferromagnetic (FM) to paramagnetic (PM) state (TC) and from metallic to insulating state (TM-I) clearly shows that transition from FM metallic to PM insulator phase goes via FM insulator phase. The Mn lattice dynamics was studied by the relative changes of Lamb-Mössbauer factor f as a function of temperature. In the Debye approximation from the calculated -ln(f /f0) values of the characteristic Debye temperatures (qD) were estimated for the FM (368(10) K) and PM (391(6) K) phases. No anomaly of –ln(f /f0) at TM-I and its rather spurious increase around TC was found. The 119Sn isotope as a local diamagnetic probe samples the transferred hyperfine field (Bhf) from its neighbour Mn magnetic moments and witnesses the dynamics of the Mn moments. Theoretical curve based on the molecular field theory was fitted to the experimental values of Bhfmax and the value of the ordering temperature (TC* » 280 K) of Mn moments inside the large FM domains was estimated. It is much higher than the TC (172 K) obtained from magnetization measurement. The coexistence of FM and PM phases, which is evident from the shape of our 119Sn Mössbauer spectra, was confirmed for temperatures T ³ 150 K and indicates the inhomogeneous character of the magnetic transition.