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MA: Magnetismus

MA 23: Spinabh
ängiger Transport III

MA 23.5: Talk

Tuesday, March 8, 2005, 11:30–11:45, TU H1028

Grain-boundary transport in polycrystalline ferromagnetic manganites with varied T_C — •R. B. Gangineni, K. Dörr, K. Nenkov, K. -H. Müller, and L. Schultz — IFW Dresden, PB 270116, 01171 Dresden

The grain-boundary magnetoresistance of several (non-textured) polycrystalline half-metallic manganites La_0.7A_0.3(Mn,B)O₃ (A = Sr, Pb, Ca; B = Ti, Ta, W)due to spin-polarized second-order tunneling was systematically investigated.The dependence of electrical conductance G(H) on larger applied magnetic fields(µ₀H > 1 T, above technical saturation of magnetization) can be described by a quadratic polynomial for all samples. La_0.7Sr_0.3MnO₃and La_0.6Pb_0.4MnO₃ with high Curie temperatures T_C werefound to show nearly linear field dependence of magnetoconductance, while other samples exhibit a more or less pronounced quadratic magnetoconductance term. Linear magnetoconductance in large magnetic fields up to 50 T indicates second-order tunneling and proves strong antiferromagnetic interactions of grain boundary magnetic moments [1].Interestingly, the linear magnetoconductance term decreases systematically with increasing T_C for 150 K < T_C < 365 K.
N. Kozlova et al., Physica B 346, 74 (2004)