Large pressure-induced magnetoresistance in a hybrid ferromagnet-semiconductor system : Effect of matrix modification on the spin-dependent scattering

• Magnetic nanocomposites based on MnAs clusters embedded in a chalcopyrite host usually do not exhibit large magnetoresistance (MR) at room temperature, while pronounced effects are localized at very low temperatures. In the present work, we observed an appearance of large pressure-induced negative and positive MR at room temperature in the Zn0.1Cd0.9GeAs2 hybrid system containing 10% MnAs inclusions. With the applied pressure, a substantial modification of the electron transport from semimetallic to semiconducting type occurs, followed by a subsequent structural transition at P approximate to 3.5GPa into almost metallic high-pressure phase. This picture is simultaneously supported by temperature-dependent and room temperature high-pressure transport measurements. Using a semiempirical expression, taking into account a spin-dependent scattering of charge carriers due to MnAs nanoclusters, as well as a two-band conductivity model, we have been able to partially describe the observed MR effects. The predominantly weak positive contribution at P=1GPa, which is well described in the framework of the proposed approach indicates the presence of spin-polarized charge carriers. Based on the two-band model calculations, a negative spin polarization was found at P >= 3GPa that ascribed to a structural change of the matrix. As our results indicate, an emerging MR in the structural transition region is characterized by a complex behavior. In particular, the negative part of MR demonstrates a magnetic field dependence different than Delta rho/rho (0)similar to H-2, suggesting the presence of unusual scattering mechanisms in magnetotransport.

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NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

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