YbNi2: A heavy fermion ferromagnet

Measurements of the magnetization and specific heat of YbNi2 binary alloy are reported. The DC magnetic susceptibility displays a ferromagnetic behavior with a Curie temperature TC=10.5 K, one of the highest found in Yb compounds. Moreover, the temperature dependence of the specific heat exhibits a lambda anomaly with a peak of 5.12 J/mol K at 9.4 K. The analysis also shows an additional magnetic contribution around 32 K stemming from the crystalline electric field of a quartet at Δ1=72K and a doublet at Δ2=126K, according to the splitting of the Yb3+ ion in cubic symmetry. From the magnetic contribution to the specific heat, a relatively high Kondo temperature TK=27K is estimated. Below the magnetic transition, the specific heat shows a huge value of the electronic coefficient γLT=573mJ/molK, which is a signature of a heavy fermion behavior. Therefore, this alloy is a fine example of enhanced ferromagnetism and heavy fermion behavior among Yb compounds.

► Laves phase YbNi2 alloy.
► Soft rare-Earth ferromagnet with TC=10.5K.
► A huge electronic coefficient γLT=573mJ/molK2 at low temperatures is found from the specific heat data.
► The uncommon ground state is dominated by a strong influence of the crystalline field effects.
► This alloy is a unique example of combined enhanced ferromagnetism and heavy fermion behavior.