We studied the exchange coupling and decoupling process in a nanocomposite spin system based on a 3D Heisenberg model by means of Monte Carlo numerical computation simulation. Different from the conventional micromagnetism approach in which finite elements method (FEM) is usually adopted to compute, in a top-down way, the magnetic property of micromagnetic ensemble in micron even nanometer scale our current paper presents a new approach in computing the magnetic property of above nanomagnetic ensemble. Our approach addressed a composite spin lattice structure consisting of both single spin and cluster spin built up from single spin in a bottom-up way. Two species of distinctive spins were taken into account further in order to imitate the magnetic behavior of heterogeneous ensemble. The simulation revealed the influence of exchange coupling constant Jab, the size of cluster spins d and system reduced temperature t upon the exchange coupling and decoupling between component spin phases, respectively. Smaller value of Jab, larger d and lower temperature t usually lead to the decoupling of originally exchange-coupled component phases and the occurrence of a characteristic two-stage shoulder with an inflexion on the demagnetization curve. The results reported here are, to some extent, of universality and applicable to other dual-phase magnetic systems since our simulation simply focus on a pure duplex spin system rather than a specific material, and all physical variables were treated in a reduced form.
Nanoscale magnetometry using a single-spin system in diamond
