  This study investigates the anisotropic effects on a system of three qubits
with chain and ring topology, described by the antiferromagnetic Heisenberg XXX
model subjected to a homogeneous magnetic field. We explore the Stirling and
Otto cycles and find that easy-axis anisotropy significantly enhances engine
efficiency across all cases. At low temperatures, the ring configuration
outperforms the chain on both work and efficiency during the Stirling cycle.
Additionally, in both topologies, the Stirling cycle achieves Carnot efficiency
with finite work at quantum critical points. In contrast, the quasistatic Otto
engine also reaches Carnot efficiency at these points but yields no useful
work. Notably, the Stirling cycle exhibits all thermal operational regimes
engine, refrigerator, heater, and accelerator unlike the quasistatic Otto
cycle, which functions only as an engine or refrigerator.
