Effect of exchange bias on the electrical resistivity of Pd doped NiMn thin films: Two-channel Kondo system

Abstract

Electrical resistivity measurements have been carried out for both flash-evaporated reentrant spin glasses (RSGs) (Ni76−xPdx)Mn24 and Ni74.5Mn23.5Pd2, as well as Ni75Mn23Pd2, a pure SG. These measurements were carried out at temperatures down to 4K. We observed a very deep resistivity minimum at about 75K for Ni74Mn24Pd2. It was found previously [Öner et al., J. Appl. Phys. 89, 7044 (2001)] that this sample shows the largest coercivity and exchange unidirectional anisotropy among these films. In addition, magnetization measurements show that this takes place just on the border of the RSG such that it could be handled as a superparamagnetic sample. Previously it was assumed that the exchange bias created in the sample between the domains plays the dominant role in the resistivity minimum. On the other hand, in order to account for the temperature dependence of the resistivity below the minimum we have analyzed these data using the Kondo, two-channel Kondo, weak localization, and Cochrane models for structural disorder based on the Anderson mechanism. We have deduced that the two-channel Kondo model gives the best agreement with the data; a logarithmic temperature dependence Δρ(T)=βlog10(T∕TK), was observed at the temperatures below Tf accompanied by a resistivity behavior Δρ(T)=ρ0m(0)(1−αT1∕2), at lower temperatures. All parameters deduced from the fitting correlate consistently with the strength of the exchange anisotropy and coercivity in the RSG films, and thus provide a separate measure of the presence of antiferromagnetically coupled domains in these materials.