Anomalies of magnetoresistance of compounds with atomic clusters RB12 (R = Ho, Er, Tm, Lu)

The magnetoresistance and magnetization of single-crystal samples of rare-earth dodecaborides RB₁₂ (R = Ho, Er, Tm, Lu) have been measured at low temperatures (1.8–35 K) in a magnetic field of up to 70 kOe. The effect of positive magnetoresistance that obeys the Kohler’s rule Δρ/ρ = f(ρ(0, 300 K)H/ρ(0, T)) is observed for the nonmagnetic metal LuB₁₂. In the magnetic dodecaborides HoB₁₂, ErB₁₂, and TmB₁₂, three characteristic regimes of the magnetoresistance behavior have been revealed: the positive magnetoresistance effect similar to the case of LuB₁₂ is observed at T > 25 K; in the range T _N ≤ T ≤ 15 K, the magnetoresistance becomes negative and depends quadratically on the external magnetic field; and, finally, upon the transition to the antiferromagnetic phase (T < T _N ), the positive magnetoresistance is again observed and its amplitude reaches 150% for HoB₁₂. It has been shown that the observed anomalies of negative magnetoresistance in the paramagnetic phase can be explained within the Yosida model of conduction electron scattering by localized magnetic moments. The performed analysis confirms the formation of spin-polaron states in the 5d band in the vicinity of rare-earth ions in paramagnetic and magnetically ordered phases of RB₁₂ and makes it possible to reveal a number of specific features in the transformation of the magnetic structure of the compounds under investigation.