The linear Ising magnet in a strong time-dependent field

The behaviour of the one-dimensional Ising magnet (spin 12, the interaction of the nearest neighbour) at the instant change of the value and direction of the constant magnetic field is theoretically investigated. The dependence on the time of the spin averages〈Sxj〉t, 〈SxjSxj+m〉t, 〈SyjSyj+1〉t and 〈SzjSzj+1〉t are rigorously calculated, where Z is the axis of the exchange interaction anisotropy. The asymptotic behaviour of the density matrix at t → ∞ is analysed and the nonergodic behaviour of the Ising system and the existence of the reducing in its statistical description are pointed out.