The basic properties (saturation moments, Curie temperatures, anisotropy constants) and magnetic reversal processes have been studied systematically on the bulk single crystals of quasibinary solid solutions R(Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> , where R = Y, La, Ce, Sm, and Gd. The magnetic reversals have been studied also on the single crystals of similar compounds with R = Nd, Dy, and Er. The general property of all studied systems is a very high coercive force H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> connected with domain wall pinning in compounds of quasibinary region. The H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (x) dependenses for all systems are similar qualitatively. There exists a maximum of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> in region x = 0.6 - 0.7 for compounds with trivalent R, and in region x = 0.3 - 0.4 for compounds with tetravalent R. The single exception is the Gd system, where H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> has rather low values for all x. The explanation is suggested for H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (x) dependence in which the compositional heterogeneities are considered as the main reason of domain wall pinning in the quasibinary compounds. These heterogeneities are always present as a result of statistical nature of Ni substitutions for Co.