Berlin 2005 – wissenschaftliches Programm

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MA: Magnetismus

MA 23: Spinabh
ängiger Transport III

MA 23.9: Vortrag

Dienstag, 8. März 2005, 12:30–12:45, TU H1028

Field dependence of colossal magnetoresistance in magnetic fields up to 50 T — •N. Kozlova, K. Dörr, K.-H. Müller, P. Reutler, R. Klingeler, B. Büchner, and L. Schultz — IFW Dresden, Postfach 270116, 01171 Dresden

The magnetoresistance of La_0.7Sr_0.3MnO₃ and La_0.7Ca_0.3MnO₃ epitaxial films and of a La_0.75Ca_0.25MnO₃ single crystal were investigated in pulsed magnetic fields up to 50 T over a wide temperature range. The Brillouin scaling model of Refs. [1] and [2] based on Mott hopping of electrons between magnetic clusters has been applied to analyze the magnetoresistance data. It has been shown that this model works well a) in the paramagnetic state above T_C and b) in a low temperature window (0.2 < T/T_C <  0.9). Near the ferromagnetic transition temperature T_C systematic deviations, in particular in larger fields, indicate that the model fails there, since neither the field dependence of magnetization nor resistance follows a Brillouin function. The temperature-dependent average magnetic moment of clusters is similar for all of our samples, but differs essentially from that obtained earlier for half-doped manganites.

[1] P. Wagner et. al., Phys. Rev. B 55 (1997) 3699.

[2] P. Wagner et. al., Phys. Rev. Lett. 81 (1998) 3980.