A. S. Carriço

Interface roughness effects on coercivity and exchange bias

We report model calculations of the hysteresis loops of exchange-coupled ferromagnet/antiferromagnet bilayers with monolayer-scale roughness and show that the loops are affected by the combined effect of the interface field strength, the degree of magnetic roughness and magnetostatic effects. The magnetization reversal may occur via domain-wall nucleation at the edges of monoatomic interface steps or coherent magnetization rotation. A magnetic phase diagram is constructed for a 10-nm-thick Fe film, subjected to nanometer-scale interface roughness.

Magnetic Particles in Biotechnology: From Drug Targeting to Tissue Engineering

In most applications reported in the literature, magnetic systems are typically composed of an inorganic core and an organic coating. Although cores have been made from different materials, iron oxide nanoparticles constituted of magnetite (Fe3O4) and maghemite (γFe2O3) are used at a great extent. While the core provide nanocontainers with magnetic properties, the shell functions to (i) protect against core agglomeration, (ii) provide chemical handles for the conjugation of drug molecules, and (iii) limit opsonization. Additionally, shell coatings have been engineered to enhance pharmacokinetics and tailor in vivo fate. Organic shells main comprise phospholipid bilayered membranes or polymeric coating of dextran, for instance. Magnetic system design with such different materials can be achieved via a number of approaches, including in situ coating, post-synthesis adsorption and endgrafting. In fact, several methods have been proposed for their synthesis, coating, and stabilization, mainly comprising the precipitation route together with a surface functionalization step by means of polymers or surfactants. This point will be the focus of the next chapter section – “Producing magnetic particles.”

Nucleation of vortex pairs in exchange biased nanoelements

We report a theoretical investigation of interface effects in the magnetic order of interface biased iron and Permalloy™ elliptical nano-elements. Contrary to intuition, there is a partial pinning of the interface layer, favoring double vortex states along the hysteresis loop. Interface biasing affects the relative chirality and the distance of the vortices. Unbiased nanoelements may nucleate vortex pairs with the same chirality separated by an antivortex. For interface biased nanoelements the vortex pair forms with opposite chirality separated by a magnetic domain.

Drug Targeting and other Recent Applications of Magnetic Carriers in Therapeutics

. Aqueous suspensions containing small magnetic particles have been increasingly used in biosciences and biotechnology. Magnetic particles develop magnetic polarization and magnetophoretic mobility, and because of such unique properties, these carriers may be eligible candidates for delivering drugs to specific sites within the body. Their special properties also allow other uses, such as those in embolization, radioisotope delivery, magnetic cell tracking for monitoring cell therapy, magnetofection, and hyperthermia. This review focuses on a discussion about magnetic particles, the properties and fate of magnetic carriers, the methods used to produce and characterize them, and their other uses in biotechnology.

Development of superparamagnetic microparticles for biotechnological purposes.

Aqueous suspensions containing magnetic microparticles have been increasingly used in biosciences and biotechnology. This work describes an experimental procedure to produce superparamagnetic microparticles. The particles were prepared based on the coprecipitation of iron salts in alkaline medium. Afterwards, characterization was performed. Characterization data demonstrated that magnetite was the dominant phase in the analyzed sample, and 50% of them were in the size range of 0.5–5μm. The results suggest that the experimental protocol provided a simple synthesis route to produce superparamagnetic microparticles. Such properties may be very useful for biotechnological purposes.

Magnetite content evaluation on magnetic drug delivery systems by spectrophotometry: a technical note.

Magnetic polymer particles have been widely used in alarge number of biotechnology and biomedicine applications(1–3). In modern pharmacy, basic investigations for themanufacturing and characterization of new dosage forms arefrequently performed using magneticfillers and drug carriers,which can be classified as the artificial sources of magneticfields. These sources are most typically based on magnetite,iron (III)γ-oxide, and barium ferrite (4)

Breathing domain wall mode of an interface pinned Neel wall

Abstract A step defect at the interface between a two – sublattice antiferromagnetic substrate and a uniaxial ferromagnetic thin film stabilizes a Neel wall. Breathing domain wall modes (BDWM) are studied with the external field in the plane of the film. The restoring force of the domain wall excitations originates from the interface exchange energy within the domain wall. For low anisotropy ferromagnets there is a significant reduction of the domain wall width and the frequency of the domain wall excitations is determined from the interface exchange coupling in a small interface area. For strong interface coupling, the width of the domain wall excitation spectrum scales with the square root of the ratio between the interface effective exchange field and the anisotropy field of the ferromagnetic film.

Controlling the vortex core of thin Permalloy nano-cylinders dipolar coupled to Co polarizers

We report a theoretical study of the vortex profile of in-plane magnetized PyTM nano-cylinders subjected to the stray field of perpendicular anisotropy Co nano-cylinders. We consider 6 nm thick PyTM cylinders dipolar coupled to 60 nm thick Co cylinders, at distances from 1.5 nm to 30 nm, with diameters (D) ranging from 45 nm to 105 nm. We find considerable reduction of critical diameter for stable PyTM magnetic vortices and spiral-vortex phases, as well as vortex core diameters twice as large as the bulk value.

Controlling the core-to-core distance of vortex pairs in exchange-biased iron elliptical nanoelements

We report a theoretical study of vortex pairs in exchange-biased elliptical iron nanoelements. We show that the remanent state may be tailored to fit vortex pairs with opposite chiralities separated by a diamond-like domain. Flat nanoelements with lateral dimensions ranging from 115 nm × 425 nm to 195 nm × 425 nm have the core-to-core distance tunable by the interface field strength.

Depinning field of a periodic domain wall array in vicinal nanowires

We report a theoretical investigation of the magnetic states and depinning field of a periodic array of head-to-head domain walls of flat Fe rectangular nanowires, exchange coupled with a vicinal two-sublattice uniaxial antiferromagnetic substrate. We show that for strong interface exchange energy, domain walls are pinned at interface steps perpendicular to the antiferromagnetic easy axis, separating terraces with opposite interface exchange field. The array sequence, which alternates head-to-head and tail-to-tail domain walls, may form a structure with alternate chirality or with the same chirality. The domain wall dipolar field affects the chirality sequence, which is tunable by the geometrical constraints and the strength of the interface exchange field. The depinning field of 10 nm thick, 1 μm long wires, with widths of 100 and 200 nm, is of the order of the interface field strength, and the depinning process involves domain wall motion and the transversal displacement of a periodic array of vortices.