The crystal structure, the temperature and field dependences of the magnetization M and of the magnetic contribution into the entropy ΔSm , the temperature dependences of high-field susceptibility χ and heat capacity Cp of specimens of polycrystal R(Co1 - xFex )2 compounds, where R is Gd, Dy, Ho, Er, are studied. The width of the ΔSm peak at half-height of its maximum (ΔTFWHM) is estimated. The dependences of ΔTFWHM and of the temperature behavior of ΔSm of the specimens on the magnetic field, the iron content (x) and the atomic number of the element R are determined. The causes of the broadening of the ΔSm(T) peak upon substitution of cobalt with iron in the R(Co1 - xFex )2 compounds are considered.