Magnetoresistance in GdNi: Magnetic-polaronic-like effect near the Curie temperature and low-temperature sign reversal

The results of magnetoresistance (Δρ/ρ) measurements in GdNi, in the temperature range 4.2 to 300 K, are reported. The sign of Δρ/ρ above the Curie temperature (${\mathrm{T}}_{\mathrm{C}}$=70 K) is negative and its magnitude in a magnetic field of 80 kOe grows with decreasing temperature below 150 K with a peak value of about -20% at ${\mathrm{T}}_{\mathrm{C}}$. These features, qualitatively resembling those in giant magnetoresistance systems (manganates), are attributed to the formation of some kind of magnetic polarons induced by Gd. The magnetoresistance changes sign below 12 K which is attributed to subtle band-structure effects.