Magnetic ordering, thermal stability, and hysteresis behaviour in a nested fullerene C 24 system: a Monte Carlo study

This work investigates the magnetic behaviour of a nested C24 fullerene system featuring mixed spins (S = 2 and σ = 5/2) using Monte Carlo simulations based on the Blume-Capel Ising model. The ground state, identified from an analysis of 30 spin configurations, is primarily governed by the competition between the crystal field (d) and the external magnetic field (h). Thermal analyses reveal a stable ferrimagnetic phase characterised by two first-order transitions: a reentrant transition (tr) followed by a paramagnetic transition at the Néel temperature (tN). The presence of field-induced first-order transitions is corroborated by step-like magnetisation hysteresis loops. Increasing the magnitudes of the exchange couplings (|r| and p) enhances both the magnetic rigidity and coercivity of the system. Conversely, the ferrimagnetic order is suppressed either by sufficiently negative crystal fields or elevated temperatures. This study provides detailed insight into the ordering mechanisms and thermal stability of the system, highlighting its potential for novel applications in spintronics.