Magnetoresistance in canonical spin-glasses

The transverse magnetoresistance (TMR) Δρρ has been measured in AuFe, AuMn, CuMn, and AgMn spin-glasses in the temperature range 1.5 to 77 K and magnetic fields up to 18 kG. All the alloys exhibit a negative TMR at all temperatures and fields and changes with field H as Hⁿ, where n2 at low fields and $1<n<2$ at higher fields. Below the spin-glass freezing temperature T₀ and at higher fields, the TMR is nearly independent of temperature. This behavior is very similar to that of the Hall resistivity. At low fields it varies smoothly around T₀ without showing any anomaly. However, below T₀ the TMR shows a somewhat stronger temperature dependence in a few alloys. Above T₀, |Δρρ| decreases with temperature and becomes undetectable beyond Tₘ, the temperature of the resistance maximum of the alloy. Also, |Δρρ| increases with the impurity concentration c in AuFe while decreasing with it in AuMn, CuMn, and AgMn. However, |Δρ| increases monotonically with c in all the systems. A recent theory of magnetoresistance, based on an Edwards-Anderson-type model for a spin-glass, explains most of the above characteristic features. This theory has been applied to compute the values of the s-d exchange parameter "J." They are in reasonable agreement with those found by earlier authors. Effects of field cooling, remanence, aging, and annealing on the TMR are discussed. A fresh annealing and quenching of AuFe alloys significantly reduces |Δρρ|.