Investigation of the Effect of Magnetic Field on Surface Phase Transition in Antiferromagnetics by Computer Simulation.

In this work, computer modeling of the surface phase transition in semi-infinite antiferromagnetic systems under the influence of external magnetic field is carried out. Cases of different values for the surface exchange integral and exchange integral for interaction between surface spins and the first subsurface layer are considered. For the surface phase transition, as for the bulk transition, the Néel temperature decreases with increasing magnetic-field intensity according to the quadratic law. The rate of decrease in the transition temperature is determined by the ratio of exchange integrals on the surface and in the bulk. For each ratio of the exchange integrals, there is a magnetic-field intensity limit above which the surface of the system does not transit into the antiferromagnetic phase. The limiting value of the magnetic field for the surface transition is no lower than the same value for the bulk. There is an interval of the magnetic-field intensity in which the antiferromagnetic ordering of spins is possible only in a thin surface layer. A tricritical point on the system phase diagram is present at the same value of the ratio of the exchange integrals for all magnetic-field-intensity values. The tricritical temperature also decreases in accordance with quadratic law with increasing magnetic-field intensity. [ABSTRACT FROM AUTHOR]