Figure
3 shows the magnetization (
M), susceptibility (
χ), and the critical temperature (
TC) of the bilayer system under the influence of the exchange interaction
Jcd with other fixed parameters ∣
Jz∣/∣
Jab∣ = 0.8,
h/∣
Jab∣ = 0.5. Figure
3(a) shows the variation of magnetization with
Jcd. Just one saturation is observed, so a conclusion can be drawn that
M is not sensitive to the variation of interlayer exchange interaction
Jcd. The
M curve holds a constant when
Jcd/∣
Jab∣ = 2.0 for
T is lower (0 ∼ 1), while with the decreasing of the value of
Jcd/∣
Jab∣, this phenomenon gradually becomes inconspicuous. In the perspective of theory, the magnetization is presented under the interaction of exchange coupling, temperature, and external magnetic field. A larger exchange coupling value is more advantageous in competition with temperature, which causes the spins in the sublattice to align in its direction, thus showing a stable magnetization externally. However, when the exchange coupling decreases or the temperature increases, the spins have more chance to flit, so the magnetization changes for the response. It gradually decreases with the increase in temperature, and at the same temperature, it decreases with the decrease of
Jcd/∣
Jab∣. A similar phenomenon can also be seen in [
38,
58]. The total susceptibility of the system varying with
Jcd is displayed in figure
3(b). The six
χ curves have the same shape. As the temperature rises,
χ first increases and then gradually decreases after reaching a peak. The increase of
Jcd/∣
Jab∣ can cause the position of the peak to shift to a higher temperature region. Physically, with the increase of
Jcd/∣
Jab∣, more thermal energy is needed to overcome the forces from exchange coupling to break the magnetic order, thus
TC increases correspondingly. For a deeper understanding of the variation of
TC with
Jcd, the
TC curve is plotted in the (
TC −
Jcd/∣
Jab∣) plane. In figure
3(c), a smooth curve can be seen. With the increase of
Jcd/∣
Jab∣, the curve gradually extends upward. In addition, the
TC curve splits the entire phase plane into two parts, with the ferromagnetic phase below
TC and the paramagnetic phase above
TC. A similar phenomenon can be seen in [
47,
48].