Dresden 2003 – wissenschaftliches Programm

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MA: Magnetismus

MA 30: Spinabh
ängige Transportph
änomene II

MA 30.8: Vortrag

Freitag, 28. März 2003, 12:30–12:45, HSZ/401

Intergrain magnetoresistance and resistance relaxation of La_0.7Sr_0.3MnO₃ in pulsed magnetic fields up to 50 T — •N. Kozlova, K. Dörr, D. Eckert, A. Handstein, Y. Skourski, T. Walter, K.-H. Müller, and L. Schultz — IFW Dresden, Postfach 270116, 01171 Dresden

Resistance of a non-textured polycrystalline La_0.7Sr_0.3MnO₃ thin film has been measured in magnetic fields H up to 47 T between 4.2 K and 300 K. The observed linear field dependence of the magnetoconductance at temperatures T < 100 K and magnetic fields above 1 T is consistent with the transport model of second-order tunneling through grain boundaries [S. Lee et al., Phys. Rev. Lett. 82, 4508 (1999)]. The grain boundary susceptibility has been derived from the conductance slopes dG/dH . Time-dependent resistance R(t) recorded after field pulses of 7 T and 47 T, show pronounced relaxation of approximately logarithmic type, for comparison, resistance relaxation has also been measured in a SQUID magnetometer, yielding similar relaxation rates. An unusual increase of the relaxation rate with decreasing temperature down to 4.2 K is observed. While polycrystalline samples show this type of relaxation, it is absent in an epitaxial film, indicating its origin in the grain boundary regions between misaligned grains. Slow relaxation might be caused by spin glass-like magnetic order at grain boundaries.

The work is supported by BMBF project 03 SC5 DRE.