Ex situ and in situ Magnetic Phase Synthesised Magneto-Driven Alginate Beads

[EN] Biocompatible magnetic hydrogels provide a great source of synthetic materials, which facilitate remote stimuli, enabling safer biological and environmental applications. Prominently, the ex situ and in situ magnetic phase integration is used to fabricate magneto-driven hydrogels, exhibiting varied behaviours in aqueous media. Therefore, it is essential to understand their physicochemical properties to target the best material for each application. In this investigation, three different types of magnetic alginate beads were synthesised. First, by direct, ex situ, calcium chloride gelation of a mixture of Fe3O4 nanoparticles with an alginate solution. Second, by in situ synthesis of Fe3O4 nanoparticles inside of the alginate beads and third, by adding an extra protection alginate layer on the in situ synthesised Fe3O4 nanoparticles alginate beads. The three types of magnetic beads were chemically and magnetically characterised. It was found that they exhibited particular stability to different pH and ionic strength conditions in aqueous solution. These are essential properties to be controlled when used for magneto-driven applications such as targeted drug delivery and water purification. Therefore, this fundamental study will direct the path to the selection of the best magnetic bead synthesis protocol according to the defined magneto-driven application.Authors acknowledge the MaMi project, funded by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 766007. We acknowledge funding support from “Ministerio de Ciencia y Educación de España” under grant PID2020-120313 GB-I00 / AIE / 10.13039/501100011033, and Gobierno Vasco Dpto. Educación for the consolidation of the research groups (IT1271-19). Special thanks to Prof. J. M. D. Coey for his help during the work performed in his laboratories and to (SGIker) of the University of the Basque Country (UPV/EHU) and Dr. Francisco Bonilla from CIC energiGUNE (Spain) for the technical support

Magnetic study of Fe3O4 nanoparticles incorporated within mesoporous silicon

Porous silicon PS matrices with oriented, separated pores grown perpendicular to the surface are used as a template for the incorporation of magnetite nanoparticles. The Fe3O4 particles used for infiltration into the PS template are coated with oleic acid in a hexane solution and exhibit an average diameter of 8 1.5 nm. The narrow size distribution and the superparamagnetic behavior at room temperature are interesting features of these nanoparticles. In addition, the use of PS as a template for the particle deposition influences and modifies the collective magnetic response of the nanoparticles. Especially, anisotropy between the two magnetization directions, magnetic field parallel and perpendicular to the surface, has been observed. Magnetite nanoparticles play a key role in medical applications, but also the magnetic properties of such a nanoparticle/PS system are of technical interest due to the transition between superparamagnetic and ferromagnetic behaviors. Temperature-dependent magnetization measurements are used to gain information about the magnetic interaction of the particles

A facile "bottom-up" approach to prepare free-standing nano-films based on manganese coordination clusters

We present herein a novel method to prepare free-standing Dried Foam Films (DFFs) whereby individual polynuclear manganese complexes cover quantitatively the holes of micro-grids; the fabricated, homogeneous films have a cross-sectional thickness of only ca. 5 nm and are characterised by high mechanical stability

Hierarchical elasticity of bimesogenic liquid crystals with twist-bend nematic phase

in 2001, Dozov predicted that twist-bend nematic phase can be spontaneously formed when K 33??2, and this phase has recently been discovered in bimesogens. To verify Dozov\u27s hypothesis, we have measured precisely the temperature dependence of the elastic constants of CB7CB in the entire temperature range of nematic phase and in twist-bend nematic phase close to the transition temperature by combing the Fr?edericksz threshold methods for a twist nematic and an in-plane switching cells. Anomalous changes in K 22 and K 33 are observed across the phase transition. The elasticity estimated via extrapolation of the data in the high temperature region of the nematic phase seems to fully satisfy Dozov\u27s hypothesis although the elasticity data in the vicinity of the phase transition exhibit opposite trends. This can be explained by the general nature of a hierarchical system where the macroscopic elasticity is governed mostly by the distortion of a higher level structure

Conventional and inverse magnetocaloric effects in La(0.45)Sr(0.55)MnO(3) nanoparticles

The magnetocaloric effect of La(0.45)Sr(0.55)MnO(3) nanoparticles was studied by dc magnetization measurements. A sample with mean particle size of about 140 nm exhibits both a conventional magnetocaloric effect around the Curie temperature (approximate to 295 K) and a large inverse magnetocaloric effect around the antiferromagnetic-ferromagnetic transition temperature (approximate to 200 K). The change of magnetic entropy increases monotonically with applied magnetic field and reaches the values of 5.51 J/kg K and - 2.35 J/kg K at 200 K and 295 K, respectively, in an applied field of 5 T. The antiferromagnetic-ferromagnetic transition is absent in a 36 nm size sample, which shows only a broad ferromagnetic transition around 340 K and a small change in magnetic entropy near room temperature. The results are discussed in terms of the entropy difference between the A-type antiferromagnetic ground state of La(0.45)Sr(0.55)MnO(3) and the low moment ferromagnetic state. By comparing the results obtained on nanoparticles and bulk La(0.45)Sr(0.55)MnO(3), one can conclude that the inverse magnetocaloric effect in a material showing the antiferromagnetic-ferromagnetic transition could be improved over a wide range of temperature by tuning the spin disorder in the antiferromagnetic state

Biaxial strain-induced transport property changes in atomically tailored SrTiO3 -based systems

Several metallic SrTiO3-based systems, including reduced SrTiO3??, Nb-doped SrTiO3, and two-dimensional electron gas at the LaAlO3/SrTiO3(001) interface, have been epitaxially fabricated on various substrates inducing different strain, from ?2.98% (compressive) to +0.99% (tensile). For all the SrTiO3-based systems, strain reduces conductivity. Tensile strain, however, is much more effective at reducing conductivity compared to compressive strain. Further, carrier mobility is found to be more sensitive to strain than carrier density. Calculations based on density functional theory show that strain can break the cubic symmetry of TiO6 octahedron, lift the degeneracy of Ti3d orbitals, and reduce the number of available states at the bottom of the conduction band to cause low carrier mobility. Our results show the critical features of strain effect on the conducting SrTiO3-based systems, and shed some light on strain engineering of these functional materials

Structural variation in cation-assisted assembly of high-nuclearity Mn arsonate and phosphonate wheels

Comproportionation reactions between MnCl2 and KMnO4 in the presence of arsonate or phosphonate ligands promote the cation-assisted assembly of high-nuclearity, wheel-shaped or toroidal {Mn8} (1) and {Mn24} (2) complexes; the closely corresponding reaction systems provide insights into the complexation behaviour of homologous phosphonate/arsonate ligand species

Magnetization and anisotropy of cobalt ferrite thin films

The magnetization of thin films of cobalt ferrite frequently falls far below the bulk value of 455kAm?1, which corresponds to an inverse cation distribution in the spinel structure with a significant orbital moment of about 0.6?B that is associated with the octahedrally coordinated Co2+ ions. The orbital moment is responsible for the magnetostriction and magnetocrystalline anisotropy and its sensitivity to imposed strain. We have systematically investigated the structure and magnetism of films produced by pulsed-laser deposition on different substrates (TiO2, MgO, MgAl2O4, SrTiO3, LSAT, LaAlO3) and as a function of temperature (500?700?C) and oxygen pressure (10?4?10Pa). Magnetization at room-temperature ranges from 60 to 440kAm?1, and uniaxial substrate-induced anisotropy ranges from +220kJm?3 for films on deposited on MgO (100) to ?2100kJm?3 for films deposited on MgAl2O4 (100), where the room-temperature anisotropy field reaches 14 T. No rearrangement of high-spin Fe3+ and Co2+ cations on tetrahedral and octahedral sites can reduce the magnetization below the bulk value, but a switch from Fe3+ and Co2+ to Fe2+ and low-spin Co3+ on octahedral sites will reduce the low-temperature magnetization to 120kAm?1, and a consequent reduction of Curie temperature can bring the room-temperature value to near zero. Possible reasons for the appearance of low-spin cobalt in the thin films are discussed

Magnetism in hafnium dioxide

Thin films of HfO2 produced by pulsed-laser deposition on sapphire, yttria-stabilized zirconia, or silicon substrates show ferromagnetic magnetization curves with little hysteresis and extrapolated Curie temperatures far in excess of 400 K. The moment does not scale with film thickness, but in terms of substrate area it is typically in the range 150?400 ?B nm?2. The magnetization exhibits a remarkable anisotropy, which depends on texture and substrate orientation. Pure HfO2 powder develops a weak magnetic moment on heating in vacuum, which is eliminated on annealing in oxygen. Lattice defects are the likely source of the magnetism