Magnetic and magnetoresistive behavior of the ferromagnetic heavy fermion YbNi₂

We present a study on the magnetic susceptibility $\chi(T)$ and electrical resistance, as a function of temperature and magnetic field $R(T,H)$, of the ferromagnetic heavy fermion YbNi$_2$. The X-ray diffraction analysis shows that the synthesized polycrystalline samples crystallizes in the cubic Laves phase structure C15, with a spatial group $Fd\overline{3}m$. The magnetic measurements indicate a ferromagnetic behavior with transition temperature at 9 K. The electrical resistance is metallic-like at high temperatures and no signature of Kondo effect was observed. In the ferromagnetic state, the electrical resistance can be justified by electron-magnon scattering considering the existence of an energy gap in the magnonic spectrum. The energy gap was determined for various applied magnetic fields. Magnetoresistance as a function of applied magnetic field, subtracted from the $R(T,H)$ curves at several temperatures, is negative from 2 K until about 40 K for all applied magnetic fields. The negative magnetoresistance originates from the suppression of magnetic disorder by the magnetic field.