Electrical resistivity singularities and spin reorientation transitions in Pr2(Co1-xFex)17

Abstract

The temperature- and field-induced spin reorientation transitions in uniaxial ferromagnetic Pr2(Co1-xFex)17 pseudo-compounds are studied using high-accuracy measurements of the electrical resistivity derivatives d rho /dT and d rho /dH. This technique avoids the need for single crystal samples. For x=0.2, a first-order spin reorientation transition is precisely located at Tsr=190K, where a sharp peak occurs in d rho /dT. The spontaneous magnetisation Ms then rotates abruptly from the basal plane to the c axis. A minute discontinuity was found in the resistivity at Tsr, Delta rho / rho approximately=0.003. For x=0, no spin reorientation transition is observed, confirming previous (single crystal) information that Ms always sits in the basal plane. For x=0.2 and T=77K, a field-induced spin reorientation transition was observed for a critical value H.c=5.0+or-0.2 kG, with a pronounced anomaly in d rho /dH. This just corresponds to the first-order Ms rotations inside those particular crystallites with c parallel to H (hard direction). Theoretical considerations are developed to characterise the anomalies associated with the spin reorientations in polycrystalline samples.