2021/06/27 by Manish Anand, Anand, Manish
Engineering · #Advanced Theoretical and Applied Studies in Material Sciences and Geometry #Characterization and Applications of Magnetic Nanoparticles #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
paper · pdf · doi:10.48550/arxiv.2106.14271
openalex publication_date 2021/06/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We study the relaxation characteristics in the two-dimensional (lx × ly) array of magnetic nanoparticles (MNPs) as a function of aspect ratio Ar=ly/lx, dipolar interaction strength hd and anisotropy axis orientation using computer simulation. The anisotropy axes of all the MNPs are assumed to have the same direction, α being the orientational angle. Irrespective of α and Ar, the functional form of the magnetization-decay curve is perfectly exponentially decaying with hd≤0.2. There exists a transition in relaxation behaviour at hd≈0.4; magnetization relaxes slowly for α≤45^∘; it relaxes rapildy with α>45^∘. Interestingly, it decays rapidly for hd>0.6, irrespective of α. It is because the dipolar interaction promotes antiferromagnetic coupling in such cases. There is a strong effect of α on the magnetic relaxation in the highly anisotropic system (Ar≥25). Interesting physics unfolds in the case of a huge aspect ratio Ar=400. There is a rapid decay of magnetization with α, even for weakly interacting MNPs. Remarkably, magnetization does not relax even with a moderate value of hd=0.4 and α=0^∘ because of ferromagnetic coupling dominance. Surprisingly, there is a complete magnetization reversal from saturation (+1) to -1 state with α>60^∘. The dipolar field and anisotropy axis tend to get aligned antiparallel to each other in such a case. The effective Néel relaxation time τN depends weakly on α for small hd and Ar≤25.0. For large Ar, there is a rapid fall in τN as α is incremented from 0 to 90^∘. These results benefit applications in data and energy storages where such controlled magnetization alignment and desired structural anisotropy are desirable.