The magnetic phase diagrams of the hexagonal intermetallic ferrimagnet
HoCo3Ni2 showing the spin reorientation transition are presented. The
diagrams have been calculated from the thermodynamic potential includ
ing the exchange energy as well as the anisotropy energy, taking into
consideration the second and fourth-order anisotropy terms. The obtain
ed phase diagrams differ substantially from those of the isotropic or
uniaxial ferrimagnets. In fields parallel to the basal plane, the new
cone-canting phase with constant susceptibility has been found in the
spin reorientation range. In fields parallel to the hexagonal axis the
re exists a narrow link between low and high-field canted phases. The
existence of the new cone-canting phase has been confirmed by magnetiz
ation measurements on a single crystal using both ballistic and SQUID
magnetometers.