Electrical magnetotransport properties in RCo12B6 compounds ( R=Y , Gd, and Ho)

Abstract

Remarkable electronic transport and magnetotransport properties are found in the intermetallic compounds $R{\mathrm{Co}}_{12}{\mathrm{B}}_{6}$ ($R=\text{Y}$, Ho, and Gd). Detailed resistivity, magnetoresistance, and Hall effect measurements are reported in the temperature range between 2 and 320 K under applied magnetic fields up to 9 T. Auxiliary magnetization results and structural data are also reported. The magnetic ordering observed in these systems depends on the rare-earth atom. In the ${\mathrm{YCo}}_{12}{\mathrm{B}}_{6}$ compound, a ferromagnetic-type ordering is observed (${T}_{C}\ensuremath{\approx}149$ K) whereas the ${\mathrm{GdCo}}_{12}{\mathrm{B}}_{6}$ and ${\mathrm{HoCo}}_{12}{\mathrm{B}}_{6}$ compounds show ferrimagnetic-type ordering (${T}_{C}\ensuremath{\approx}162$ and 144 K, respectively) and their magnetization exhibits the compensation phenomenon. All compounds show high residual-resistance ratio (RRR) rates and resistivities typical of magnetically ordered systems, with a characteristic downward inflection at the critical temperature. The resistivity results are described in terms of the interplay between the electron-phonon interaction and a magnetic term. The magnetoresistance is consequence of a complex superposition of effects due to conduction in spin-polarized bands and to spin-disorder suppression. A strong positive contribution, which prevails at low temperatures, is described with a basis on the Campbell-Fert model that assumes conduction by two spin-polarized currents with a spin-mixing term. The usual negative effect related to suppression of spin disorder becomes the dominant contribution at intermediate- and high-temperature regimes. At low temperatures, the Hall resistivity results are also consistent with conduction by two spin-polarized bands. Moreover, a sign reversal observed in the Hall resistivity for all compounds at low temperatures indicates that the majority spin-up band is holelike, while the minority spin band is electronlike. The ordinary and anomalous Hall contributions could be separated. The intrinsic Karplus-Luttinger mechanism is the most relevant contribution to the anomalous Hall resistivity in all studied compounds. However, an additional term due to chiralities related to canting of the Co moments also plays a role in the temperature region near ${T}_{C}$.