Magnetic properties and the crystal field problem for tetragonal HoBa(2)Cu(3)O(x).

Magnetic susceptibilities of the first and third orders as well as the magnetization of the singlet paramagnet HoBa(2)Cu(3)O(x) (x≈6.0) at low temperatures are studied experimentally using a SQUID magnetometer and compared with theoretical calculations. The magnetic behaviour of single-crystal HoBa(2)Cu(3)O(x) at low temperature is found not to follow the one calculated on the basis of the known crystal field parameters. Different effects which may change the magnetic properties are analysed and discussed: low symmetry components of the crystal field due to some disorder in the oxygen subsystem, a noncompensated effective field from the ordered Cu subsystem acting on the Ho(3+) ions, and others.