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Статья

Charge transport in HoxLu1-xB12: Separating Positive and Negative Magnetoresistance in Metals with Magnetic Ions

Physical Review B: Condensed Matter and Materials Physics. 2015. Vol. 91. P. 235104-1-235104-15.
Sluchanko N., Khoroshilov A., Anisimov M., Azarevich A., Bogach A., Glushkov V., Demishev S.V., Krasnorussky V., Samarin N., Shitsevalova N., Filippov V., Levchenko A., Pristas G., Gabani S., Flachbart K.

The magnetoresistance (MR) ρ/ρ of the cage-glass compound HoxLu1−xB12 with various concentrations of magnetic holmium ions (x  0.5) has been studied in detail concurrently with magnetization M(T) and Hall effect investigations on high-quality single crystals at temperatures 1.9–120 K and in magnetic field up to 80 kOe. The undertaken analysis of ρ/ρ allows us to conclude that the large negative magnetoresistance (nMR) observed in the vicinity of the N´eel temperature is caused by scattering of charge carriers on magnetic clusters of Ho3+ ions, and that these nanosize regions with antiferromagnetic (AF) exchange inside may be considered as short-range-order AF domains. It was shown that the Yosida relation −ρ/ρ ∼ M2 provides an adequate description of the nMR effect for the case of Langevin-type behavior of magnetization. Moreover, a reduction of Ho-ion effective magnetic moments in the range 3–9 μB was found to develop both with temperature lowering and under the increase of holmium content. A phenomenological description of the large positive quadratic contribution ρ/ρ ∼ μ2 DH2 which dominates in HoxLu1−xB12 in the intermediate temperature range 20–120 K allows us to estimate the drift mobility exponential changes μD ∼ T −α with α = 1.3–1.6 depending on Ho concentration. An even more comprehensive behavior of magnetoresistance has been found in the AF state of HoxLu1−xB12 where an additional linear positive component was observed and attributed to charge-carrier scattering on the spin density wave (SDW). High-precision measurements of ρ/ρ = f (H,T ) have allowed us also to reconstruct the magnetic H-T phase diagram of Ho0.5Lu0.5B12 and to resolve its magnetic structure as a superposition of 4f (based on localized moments) and 5d (based on SDW) components.