Positive magnetoresistivity in a localized-moment ferromagnet with itinerant spin fluctuations: TmCo2

Results on electrical resistivity and magnetization of TmCo2, intermetallic compound in magnetic fields up to 15 T and in temperature range from 1.5 K to 300 K are presented. In zero magnetic field two well-separated phase tr ansitions are observed at low temperatures: at 3.7 K and at 3.3 K. Magnetor esistivity at temperatures below 3.3 K is negative. However at higher tempe ratures, magnetoresistivity is positive in a weak field, showing a maximum in the dependence on the magnetic held at H-max. H-max is found to be propo rtional to T-1.5 The maximum exists also in the temperature dependence of m agnetoresistivity, measured at a constant external field H*. The results ar e interpreted in the framework of a model with two different contributions to magnetoresistivity: a negative one, related to the localized 4f magnetic moments of Tm, and a positive contribution associated with the features of the Co 3d band which are responsible for the itinerant metamagnetism of RC o2 compounds. The positive magnetoresistivity arises due to the spin polari zation of the Co 3d band by the exchange field and enhancement of the spin fluctuations within this band. [S0163-1829(99)01425-3].