Title: BEHAVIOUR OF A THREE-DIMENSIONAL UNIAXIAL MAGNET NEAR THE CRITICAL POINT IN AN EXTERNAL FIELD
Authors: M.P.Kozlovskii, I.V.Pylyuk, O.O.Prytula (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine)

The behaviour of a three-dimensional magnet with a one-component order parameter near the critical point in a homogeneous external field is investigated. The calculations are performed in the case when the field and temperature are dependent and related by some expression (the system tends to the critical point along some trajectory). The high- and low-temperature regions in the vicinity of T_c (T_c is the phase transition temperature in the absence of an external field) are considered. It is shown that in the weak fields the system behaviour is described in general by the temperature variable, but in the case of the strong fields the role of the temperature variable is not dominant. The corresponding expressions for the free energy, susceptibility and other characteristics of the system are obtained for each of these regions.

Key words: three-dimensional uniaxial magnet, collective variables, critical behaviour, external field
PACS: 05.50.+q, 05.70.Ce, 64.60.Fr, 75.10.Hk