Abstract
The magnetoresistance of (γ-Fe2O3)xAg100−x (x=50–90), a granular system where insulating magnetic nanoparticles and nonmagnetic metal are intimately mixed, has been studied at room temperature. For high silver concentration (x⩽70), samples are metallic and exhibit ordinary positive magnetoresistance. Below the percolation threshold, which is 11.4 vol % of silver (x=71), samples are insulators. Our data suggest that direct tunneling between silver grains across γ-Fe2O3 barriers dominates at low temperature and variable range hopping becomes the main transport mechanism at high temperature. The variable range hopping within γ-Fe2O3 is believed to be associated with the presence of Fe2+ impurities which is determined by Mössbauer spectroscopy. Negative magnetoresistance up to −2% is found in (γ-Fe2O3)xAg100−x (x⩾72) in an applied field of 10 kOe at room temperature. It is proposed that the observed negative magnetoresistance is due to the field-dependent hopping rate of electrons from Fe2+ to Fe3+ which is enhanced due to the alignment of their moments by an applied magnetic field.
Highlights
Jinke Tang,a) Li Feng, and Joan A
Large magnetoresistance has been observed in metal
where two magnetic layers are spaced by a thin insulator film.[1,2] The results support the claim that large magnetoresistance is due to the spin polarized tunneling
Summary
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