The field dependence of giant magnetoresistance of AuFe alloys at low temperature

The low magnetic field H dependence of the magnetization M(T, H) and the magnetoresistance MR(T, H) of a Au,,Fe,, alloy are investigated. The magnetic Fe granules with a range of sizes are embedded in non-magnetic Au matrix. At a given temperature, a part of these magnetic granules;Ire superparamagnetic (called SPM), the others are ferromagnetic (called non-SPM). It was found that the SPM granules had a different effect on M(T, H) or MR(T, H) from the non-SPM granules. At low field, the magnetic moments of non-SPM granules are not aligned with H while the magnetic moments of SPM granules have different :probabilities along easy directions which may be parallel or antiparallel to H. We distinguish the non-SPM from SPM granules and calculate the M(T, H) and MR(T, H) when the temperature and the applied field are low. The results are in quantitative agreement with the experimental data. (C) 1999 Elsevier Science B.V. All rights reserved.The low magnetic field H dependence of the magnetization M(T, H) and the magnetoresistance MR(T, H) of a Au85Fe15 alloy are investigated. The magnetic Fe granules with a range of sizes are embedded in non-magnetic Au matrix. At a given temperature, a part of these magnetic granules are superparamagnetic (called SPM), the others are ferromagnetic (called non-SPM). It was found that the SPM granules had a different effect on M(T, H) or MR(T, H) from the non-SPM granules. At low field, the magnetic moments of non-SPM granules are not aligned with H while the magnetic moments of SPM granules have different probabilities along easy directions which may be parallel or antiparallel to H. We distinguish the non-SPM from SPM granules and calculate the M(T, H) and MR(T, H) when the temperature and the applied field are low. The results are in quantitative agreement with the experimental data. (C) 1999 Elsevier Science B.V. All rights reserved.