Strong magnetoresistance reaching thousands of percent and non-monotonic field dependent Hall effect were measured in Mn implanted Ge samples in fields up to 60 T and analyzed in the framework of a two carriers model. The measured Hall effect and temperature dependent zero field resistance can be consistently described by parallel conductance along thick p-type Ge substrate with low concentration of highly mobile carriers and along thin Mn doped Ge layer with low mobility carriers. However, the same model is not sufficient to explain experimentally observed suppression of quadratic field dependence of magnetoresistance at low fields and absence of its saturation at high fields. Two additional mechanisms were identified: a strong quasi-linear magnetoresistance of Ge substrate that dominates the low field range and a nonsaturating "3/2" power law magnetoresistance of the Mn doped Ge layer dominating the high field range. V

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Magnetization and magnetoresistance in function of the magnitude and orientation of applied magnetic field were studied in Co-Fe discontinuous multilayers close to their structural percolation. The high pulsed magnetic fields up to 33 T were used in the 120-310 K temperature range. Comparison between longitudinal and transverse ͑with respect to the film plane͒ field configurations was made in the low-field and high-field regimes in order to clarify the nature of the measured negative magnetoresistance. Coexistence of two distinct magnetic fractions, superparamagnetic ͑SPM, consisting of small spherical Co-Fe granules͒ and superferromagnetic ͑SFM, by bigger Co-Fe clusters͒, was established in this system. These fractions were shown to have different relevance for the system magnetization and magnetotransport. While the magnetization is almost completely ͑up to ϳ97%͒ defined by the SFM contribution and practically independent of temperature ͑in this range͒, the magnetoresistance experiences a crossover from a regime dominated by Langevin correlations ͑suppressed with temperature͒ between neighbor SPM and SFM moments at low fields, to that dominated by spin scattering ͑enhanced with temperature͒ of charge carriers within SFM clusters at high fields. Also, the demagnetizing effects, sensitive to the field orientation, were found to essentially define the low-field behavior and characteristic crossover field.

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