Finite Length Effects on Switching Mechanisms in Chains of Magnetic Particles

Periodic systems of magnetic nanoparticles are now of interest as they support GHz spin waves. Their equilibrium configurations, switchable with the external magnetic field, are crucial for such applications. We study infinite and finite chains of particles of two shapes (i) ellipsoidal and (ii) rectangular stripes with long axes perpendicular to the chain axis. A variable magnetic field is applied parallel to the long axes. Micromagnetic simulations are compared with the corresponding discrete spin models (Stoner-Wohlfarth model, S-W). An antiferromagnetic configuration is the ground state for all the systems at vanishing field but a ferromagnetic configuration occurs when the field is strong enough. The switching of the infinite chains to the reversed ferromagnetic configuration proceeds directly for the ellipsoids and by an intermediate configuration, in which the magnetization within the particle is non-uniform, in the case of the stripes. The non-uniform configurations are well represented by tilted states in S-W model. Important differences are found in the finite analogs: the switching of ellipsoids becomes multistage and starts from the innermost particles relatively well reproduced with S-W model, whereas the reversal of the stripes, starts from the outermost particles and has no analog in S-W model. Practical consequences of the findings are discussed

Spacing Dependent Mechanisms of Remagnetization in 1D System of Elongated Diamond Shaped Thin Magnetic Particles

Four different switching scenarios have been revealed for a linear chain of flat magnetic particles with long axes perpendicular to the axis of the chain. The diamond-like shape of the particles has been previously shown to be the best to ensure a uniform and stable magnetization within a single particle, that is, to behave as a macrospin. The occurrence of each scenario depends on the distance of the particles in the chain. Whereas long distances favor direct remagnetization of a ferromagnetic configuration “all up” to the one “all down”, a short enough distance allows the system to recover its ground state at a zero field, that is, an antiferromagnetic order. This allows any information stored by a magnetic field to be erased. Vortex-like metastable defects have been noticed for intermediate distances. A longitudinal magnetization component at extremely short distances has been noticed as well as specific systems of domain walls. The hysteresis loops and magnetization maps in the particles have been presented for each scenario. The potential applicability of the findings to the fabrication of memory storage devices has been discussed

Functionalised Anodised Aluminium Oxide as a Biocidal Agent

In this article, we describe the antimicrobial properties of a new composite based on anodic aluminium oxide (AAO) membranes containing propyl-copper-phosphonate units arranged at a predetermined density inside the AAO channels. The samples were prepared with four concentrations of copper ions and tested as antimicrobial drug on four different strains of Escherichia coli (K12, R2, R3 and R4). For comparison, the same strains were tested with three types of antibiotics using the minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests. Moreover, DNA was isolated from the analysed bacteria which was additionally digested with formamidopyrimidine-DNA glycosylase (Fpg) protein from the group of repair glycosases. These enzymes are markers of modified oxidised bases in nucleic acids produced during oxidative stress in cells. Preliminary cellular studies, MIC and MBC tests and digestion with Fpg protein after modification of bacterial DNA suggest that these compounds may have greater potential as antibacterial agents than antibiotics such as ciprofloxacin, bleomycin and cloxacillin. The described composites are highly specific for the analysed model Escherichia coli strains and may be used in the future as new substitutes for commonly used antibiotics in clinical and nosocomial infections in the progressing pandemic era. The results show much stronger antibacterial properties of the functionalised membranes on the action of bacterial membranes in comparison to the antibiotics in the Fpg digestion experiment. This is most likely due to the strong induction of oxidative stress in the cell through the breakdown of the analysed bacterial DNA. We have also observed that the intermolecular distances between the functional units play an important role for the antimicrobial properties of the used material. Hence, we utilised the idea of the 2D solvent to tailor them