Effect of Spin Fluctuations on Magnetic Properties of Frustrated Spin Chains

Using functional integral method, we investigate the magnetic properties of the
${J_1} - {J_2}$
frustrated spin chain in the presence of a longitudinal magnetic field and a single-ion anisotropy at the vicinity of zero temperature and at finite temperatures for both cases
${J_1} > 0$
and
${J_1} < 0$
. We focus on the range of the frustrated parameter where the ground state is still ferromagnetic or antiferromagnetic. From that, we discuss the significant effect of the thermal and quantum fluctuations due to the frustration and find critical values of the frustrated parameter. Thus, we see a drastic effect due to the fluctuations at the critical points, which can cause a breakdown of a given approach. We also compared the obtained results to the experimental data from Cu[ampy]Br
₂
and found an agreement between the calculated susceptibility and the experimental susceptibility, except that an antiferromagnetic phase transition is found only in the calculated susceptibility.