Magnetoresistance in dysprosium single crystals

The magnetoresistance in the ferromagnetic phase of the Dy $a$-, $b$-, and $c$-axis crystals has been investigated in magnetic fields up to 75 kOe and in the temperature range between 1-70 K. It is anisotropic with respect to the crystallographic axes and to relative orientations of the field and the current. The longitudinal isotherms exhibit a minimum which increases in depth and moves to higher fields as the temperature increases. The transverse magnetoresistance in the basal-plane crystals for fields above 20 kOe increases with the field in the entire temperature range. But for the $c$-axis crystal ($\overrightarrow{I}\parallel 〈0001〉$ and $\overrightarrow{\mathrm{H}}\parallel 〈11\overline{2}0〉 or 〈10\overline{1}0〉$) above 25 K, it decreases as field increases. These results have been discussed on the basis of scattering due to impurities, phonons, magnetic domains, and spin waves, and in terms of magnetic anisotropy of the metal. When the field is parallel to the $b$ axis, the transverse-resistance isotherms around 20-40 K show a resistance maximum of about 0.2% at a field which gradually decreases as temperature increases. The critical field for the spin-wave energy gap around 40 K, as estimated from the resistance maximum is about 10 kOe.