Anisotropic Effect of Dipolar Interaction in Ordered Ensembles of Nanoparticles

Abstract

We implement extensive computer simulations to investigate the hysteresis characteristics in the ordered arrays (l x × l y ) of magnetic nanoparticles as a function of aspect ratio A r = l y /l x , dipolar interaction strength h d , and external magnetic field directions. We have considered the aligned anisotropy case, α is the orientational angle. It provides an elegant en route to unearth the explicit role of anisotropy and dipolar interaction on the hysteresis response in such a versatile system. The superparamagnetic character is dominant with weak dipolar interaction (h d ≤ 0.2), resulting in the minimal hysteresis loop area. Remarkably, the double-loop hysteresis emerges even with moderate interaction strength (h d ≈ 0.4), reminiscent of antiferromagnetic coupling. These features are strongly dependent on α and A r . Interestingly, the hysteresis loop area increases with h d , provided A r is enormous, and the external magnetic field is along the y-direction. The coercive field µ o H c , remanent magnetization M r , and the heat dissipation E H also depend strongly on these parameters. Irrespective of the external field direction and weak dipolar interaction (h d ≤ 0.4), there is an increase in µ o H c with h d for a fixed α and A r ≤ 4.0. The dipolar interaction also elevates M r as long as A r is huge and the field is along the y-direction. E H is minimal for negligible and weak dipolar interaction, irrespective of A r , α, and the field directions. Notably, the magnetic interaction enhances E H if A r is enormous and the magnetic field is along the long axis of the system. These results are beneficial in various applications of interest such as digital data storage, spintronics, etc.