Monte Carlo Simulations On Magnetic Properties Of Disordered Nanoparticle Films

For decades, the study of the magnetic nanoparticle films has become one of the most active areas of research due to its recent advances in high-density magnetic recording techniques.In this paper, the magnetic properties of a disordered nanoparticle film with the applied magnetic field perpendicular and parallel to the film are simulated by a Monte Carlo method. The effect of both the interaction between particles and the width of anisotropy angular dispersion are considered. The main jobs and conclusions are as follows.1.When the external magnetic field is exerted perpendicular to the film, the dependence of dipole-dipole interaction(D)and exchange interaction (J) on hysteresis of nanoparticle film is simulated.It is found that in a system including only dipole-dipole interaction, the dipole-dipole interaction restrains the system to be magnetized.With the increase of the dipole-dipole interaction, the hysteresis loops are elongated horizontally along the external field direction, and the hysteresis area becomes thinner. The remanence decreases rapidly, and the coercivity decreases at first and then increases.If only exchange interaction is considered, rectangular hysteresis loops appear, and the hysteresis area increases as the exchange interaction increases, together with the coercivity and the remanence.2.When the external magnetic field is exerted parallel to the film, the dependence of dipole-dipole interaction and exchange interaction on hysteresis is simulated. It reveals that in a dipole-dipole system, with the increase of dipole-dipole interaction, the hysteresis area, the coercivity and the remanence increase, but the saturated magnetization along x direction reduces.If only exchange interaction exists in the system, the coercivity and the remanence decrease, but the saturated magnetization along x direction increase as the exchange interaction increases at certain temperature.3.The D-J graph is created to expatiate on the whole relations D-J and coercivity or remanence in the perpendicular and parallel magnetic field. It is easily found that the coercivity and remanence show complex relation with the dipole-dipole and exchange interaction.4.When the external magnetic field is exerted perpendicular to the film, the dependence of anisotropy angular dispersion on hysteresis of nanoparticle film is simulated. It is found that in a system considering weak dipole-dipole interaction, with the increase of anisotropy angular dispersion width, the coercivity, the remanence, and the saturated magnetization along z direction reduce.While the width of anisotropy angular dispersion doesn't affect the hysteresis much if the dipole-dipole interaction is strong. In the system of only exchange interaction, the hysteresis area, the coercivity and the remanence decrease with the anisotropy angular dispersion width increasing.5.When the external magnetic field is exerted parallel to the film, the effect of anisotropy angular dispersion on hysteresis of system is studied. In a system without interaction, the effect of anisotropy angular dispersion on the hysteresis is evidence, and no hysteresis effect occurs when the width of anisotropy angular dispersion is zero,while with the increase of the width of anisotropy angular dispersion, the hysteresis appears,together with the coercivity and the remanence increasing.For a system of definite dipole-dipole interaction, with the increase of the width of anisotropy angular dispersion, the coercivity and the remanence increase, but if the dipole-dipole interaction is strong, such effect becomes small.If pure exchange interaction is considered, the hysteresis area, the coercive and the remanence increase with the increase of the anisotropy angular dispersion width. The stronger the exchange interaction is, the smaller the extent of increase is.