Effect of the dipole–dipole interaction on the low-temperature magnetism of linear spin chains

Abstract

The magnetic dipole–dipole interaction in a linear chain of spins S=1∕2 with uniaxial exchange anisotropy gives raise to evolution of the system of energy levels. As the magnetic dipole interaction increases, the fastest decrease of the energy of the system is observed for a level with the maximum modulus of the spin of the system. For sufficiently large ratio of the dipole–dipole contribution to the exchange a transition occurs between the spin-gap states—antiferromagnetic and ferromagnetic. An extremely sharp change of the mean-square spin of the system at low temperatures (T<10−3J∕k) followed by a “plateau” in the temperature dependence is characteristic for a narrow neighborhood of the point at which the type of ground state changes.