We present a detailed study of the temperature dependence of the electrical resistivity [$\rho (T)$] in the range 13–300 K for the Ho${}_5$(Si${}_x$Ge${}_{1-x}$)${}_4$ system. Three distinct $\rho (T)$ behaviors are observed, associated with different magnetic and crystallographic structures along the series. In the samples with an antiferromagnetic phase (AFM) one observes a shoulder near the Néel temperature ($T_N$) attributed to the formation of a gap on the Fermi surface. This gap is analyzed using a phenomenological two-band model for an AFM with distinct atomic and magnetic periodicities, and its effect seems to extend well above $T_N$. We also found the presence of short-range magnetic clusters in the paramagnetic (PM) phase. On the ferromagnetic (FM) materials, the distinct $\rho (T)$ scattering contributions (phonon, magnetic, and residual terms) are extracted from the measurements, with $\rho (T)$ mainly dominated by electron spin scattering. An additional contribution is also observed, arising from the strong crystal field effect in these materials. The effect is mainly observed in the PM phase, leading to a curvature on $\rho (T)$ in this phase. Using a two-level crystal field model the corresponding gap was estimated for the different Si/Ge ratio samples, revealing that the crystal field splitting increases linearly with Si content.

• Received 7 August 2010

DOI:https://doi.org/10.1103/PhysRevB.83.144117