  A closed system of the equations for the local Bloch vectors and spin
correlation functions is obtained by decomplexification of the Liouville-von
Neumann equation for three magnetic qubits with the exchange interaction, that
takes place in an arbitrary time-dependent external magnetic field. The
numerical comparative analysis of entanglement is carried out depending on
initial conditions and the magnetic field modulation. The present study may be
useful for analysis of interference experiments and in the field of quantum
computing.
