Observation of ion beam induced magnetic patterning using off-specular polarized neutron reflectometry

The long-range magnetic structure in Co/Pt multilayers magnetically patterned by ion irradiation is observed by off-specular polarized neutron reflectivity. While both specular and off-specular measurements indicate the formation of an artificial domain structure when the sample is in its remanent state, resonant peaks seen in the diffuse scatter reveal long-range magnetic ordering with periodicity in agreement with the design value. These peaks are completely suppressed when the sample is saturated in plane, confirming their origin in the magnetic patterning of the multilayer

Magnetically soft, high moment grain-refined Fe films: application to magnetic tunnel junctions

The effect of N-doping on the microstructure and magnetic properties of thin Fe layers has been employed to construct all Fe-electrode magnetic tunnel junctions that displayed the tunneling magnetoresistance (TMR) effect. Using low nitrogen doses, a reduction in coercivity was achieved due to grain refinement, without a concurrent decrease in the saturation magnetization of the Fe films caused by the formation of crystalline iron nitride phases. It was demonstrated that this N-induced grain refinement can be applied beneficially to control the switching field of the "free" layer in magnetic trilayer structures. In general the ability to control magnetic softness without reducing saturation magnetization will prove important for incorporating high spin-polarized materials into spin valves and TMR devices

The cellular magnetic response and biocompatibility of biogenic zinc- and cobalt-doped magnetite nanoparticles.

The magnetic moment and anisotropy of magnetite nanoparticles can be optimised by doping with transition metal cations, enabling their properties to be tuned for different biomedical applications. In this study, we assessed the suitability of bacterially synthesized zinc- and cobalt-doped magnetite nanoparticles for biomedical applications. To do this we measured cellular viability and activity in primary human bone marrow-derived mesenchymal stem cells and human osteosarcoma-derived cells. Using AC susceptibility we studied doping induced changes in the magnetic response of the nanoparticles both as stable aqueous suspensions and when associated with cells. Our findings show that the magnetic response of the particles was altered after cellular interaction with a reduction in their mobility. In particular, the strongest AC susceptibility signal measured in vitro was from cells containing high-moment zinc-doped particles, whilst no signal was observed in cells containing the high-anisotropy cobalt-doped particles. For both particle types we found that the moderate dopant levels required for optimum magnetic properties did not alter their cytotoxicity or affect osteogenic differentiation of the stem cells. Thus, despite the known cytotoxicity of cobalt and zinc ions, these results suggest that iron oxide nanoparticles can be doped to sufficiently tailor their magnetic properties without compromising cellular biocompatibility

Broadband optical measurement of AC magnetic susceptibility of magnetite nanoparticles

This is the author accepted manuscript. The final version is available from AIP Publishing via the DOI in this recordCharacterization of magnetic nanoparticles in solution is challenging due to the interplay between magnetic relaxation and agglomeration. The AC magnetic susceptibility of magnetite nanoparticles in water has been studied using magneto-optical methods in the frequency range of 10 Hz–250 kHz. The Faraday effect is detected simultaneously with changes in the fluid configuration. It is shown that the relative sensitivity to the magnetic and structural response can be adjusted by varying the wavelength, paving the way toward spatially resolved studies at the micro-scaleEngineering and Physical Sciences Research Council (EPSRC

Nanoscale chemical speciation of β-amyloid/iron aggregates using soft x-ray spectromicroscopy

Iron (Fe) is an essential trace element required for healthy brain function. Yet, disrupted iron neurochemistry, and the associated formation of aberrantly aggregated protein lesions has been implicated in the development of multiple degenerative brain disorders including Alzheimer's disease (AD). Here, nanoscale resolution soft X-ray spectromicroscopy is used to examine the interaction of β-amyloid (Aβ), a peptide fundamentally implicated in the development of Alzheimer's, and ferric (Fe3+) iron. Crucially, by probing the carbon K (280–320 eV) and iron L2,3 (700–740 eV) edges, both the organic and inorganic (iron) sample chemistry was established. The co-aggregation of Aβ and iron is known to influence iron chemistry, resulting in the chemical reduction of Fe3+ into reactive and potentially toxic ferrous (Fe2+) and zero-oxidation (Fe0) states. Here, nanoscale (i.e. sub-micron) variations in both iron oxidation state and the organic composition of Aβ were observed, replicating in vitro the diverse iron chemistry documented in amyloid plaques from human brain, with the chemical state of iron linked to the conformation state of Aβ. Furthermore, aggregates were formed that were morphologically and chemically distinct dependent on the treatment of Aβ prior to the addition of ferric iron. These findings support the hypothesis that Aβ is responsible for altering iron neurochemistry, and that this altered chemistry is a factor in neurodegenerative processes documented in AD. The methods applied here, combining nanoscale-resolution imaging and high chemical sensitivity, enabled discovery of the nanoscale heterogeneity in the iron and carbon chemistry of in vitro aggregates, and these approaches have scope for wider application in metallomics

Iron stored in ferritin is chemically reduced in the presence of aggregating Aβ(1-42).

Atypical low-oxidation-state iron phases in Alzheimer's disease (AD) pathology are implicated in disease pathogenesis, as they may promote elevated redox activity and convey toxicity. However, the origin of low-oxidation-state iron and the pathways responsible for its formation and evolution remain unresolved. Here we investigate the interaction of the AD peptide β-amyloid (Aβ) with the iron storage protein ferritin, to establish whether interactions between these two species are a potential source of low-oxidation-state iron in AD. Using X-ray spectromicroscopy and electron microscopy we found that the co-aggregation of Aβ and ferritin resulted in the conversion of ferritin's inert ferric core into more reactive low-oxidation-states. Such findings strongly implicate Aβ in the altered iron handling and increased oxidative stress observed in AD pathogenesis. These amyloid-associated iron phases have biomarker potential to assist with disease diagnosis and staging, and may act as targets for therapies designed to lower oxidative stress in AD tissue

Remote magnetic actuation of cell signalling for tissue engineering

Magnetic nanoparticles (MNP) are extremely versatile tools in bioengineering and medicine with diverse uses ranging from magnetic resonance contrast agents to drug delivery vehicles. Recently, MNP have been adapted to target and regulate cell signalling pathways for control of cell behaviour. This approach has been applied to stem and progenitor cells to orchestrate tissue development in tissue engineering. This review introduces the bio-functionalisation mechanisms for MNP and highlights the recent advances in MNP-mediated cell signalling activation. We also explore how the application of this technology has novel uses for stem cell control in the context of tissue engineering and regenerative medicine

Correlative Spectromicroscopy and Tomography for Biomedical Applications involving Electron, Ion, and Soft X-ray Microscopies

Many important scientific and technical problems are best addressed using multiple, microscopy-based analytical techniques that combine the strengths of complementary methods. Here, we provide two examples from biomedical challenges: unravelling the attachment zone between dental implants and bone, and uncovering the mechanism of Alzheimer's disease. They combine synchrotron-based scanning transmission X-ray microscopy (STXM) with transmission electron microscopy ((S)TEM), electron tomography (ET), EELS tomography, and/or atom probe tomography (APT). STXM provides X-ray absorption based chemical sensitivity at mesoscale resolution (10–30 nm), which complements higher spatial resolution electron microscopy and APT