Structural and magnetic properties of (ultra)thin LaSrMnO films

Ferromagnetic metallic manganites are employed as prototypical spin injectors in several systems in order to reveal insights in a variety of spin related effects [1,2]. In particular, the La0.7Sr0.3MnO3 (LSMO) compound has stimulated an intense study since, in bulk form, it has one of the highest ferromagnetic transition temperature Tc = 370 K. Understanding and controlling the morpho-structural and magnetic properties of LSMO films as a function of thickness is crucial for realizing applications that commonly demand for ultrathin layers. For this purpose, LSMO films in the thickness range of 4-16 nm were deposited on single-crystal (001) SrTiO3 substrates by means of channel spark ablation [3]. The temperature and angular dependence of the magnetic properties were studied by a vector Vibrating Sample Magnetometer, in conjunction to structural and morphological results. Even the thinnest sample shows ferromagnetism (Tc = 250 K) and Tc enhances with increasing th, reaching a value of about 315 K for th = 16 nm. This gradual approach towards the ferromagnetic properties of bulk LSMO follows a strain driven trend from fully strained films with weakened magnetism towards robust magnetism with a sudden change at about 6 nm. Moreover, with increasing the temperature from 100 K up to 300 K, a change of the magnetic anisotropy from a biaxial to a dominant uniaxial symmetry was clearly observed in all the films. Such a behaviour - probably related to a crossover from a low-temperature regime, where crystalline anisotropy dominates, to a high-temperature one, governed by magnetoelastic anisotropy - occurs progressively, with a substantial isotropic behaviour actually existing in a narrow temperature range

Hanle effect missing in a prototypical organic spintronic device

We investigate spin precession (Hanle effect) in the prototypical organic spintronic giant magnetoresistance device La0.7Sr0.3MnO3/tris(8-hydroxyquinoline)/AlOx/Co. The Hanle effect is not observed in measurements taken by sweeping a magnetic field at different angles from the plane of the device. As possible explanations we discuss the tilting out of plane of the magnetization of the electrodes, exceptionally high mobility, or hot spots. Our results call for a greater understanding of spin injection and transport in such devices

Magnetic and morphological properties of ferrofluid-impregnated hydroxyapatite/collagen scaffolds

In this article we present the morphological and magnetic characterization of ferrofluid-impregnated biomimetic scaffolds made of hydroxyapatite and collagen used for bone reconstruction. We describe an innovative and simple impregnation process by which the ferrofluid is firmly adsorbed onto the hydroxyapatite/collagen scaffolds. The process confers sufficient magnetization to attract potential magnetic carriers, which may be used to transport bioactive agents that favour bone regeneration. The crystalline structure of the magnetite contained in the ferrofluid is preserved and its quantity, estimated from the weight gain due to the impregnation process, is consistent with that obtained from energy dispersive X-ray spectroscopy. The magnetization, measured with a superconducting quantum interference device, is uniform throughout the scaffolds, demonstrating the efficiency of the impregnation process. The field emission gun scanning electron microscopy characterization demonstrates that the process does not alter the morphology of the hydroxyapatite/collagen scaffolds, which is essential for the preservation of their bioactivity and consequently for their effectiveness in promoting bone formation

Biomimetic magnetic silk scaffolds

Magnetic silk fibroin protein (SFP) scaffolds integrating magnetic materials and featuring magnetic gradients were prepared for potential utility in magnetic-field assisted tissue engineering. Magnetic nanoparticles (MNPs) were introduced into SFP scaffolds via dip-coating methods, resulting in magnetic SFP scaffolds with different strengths of magnetization. Magnetic SFP scaffolds showed excellent hyperthermia properties achieving temperature increases up to 8 degrees C in about 100 s. The scaffolds were not toxic to osteogenic cells and improved cell adhesion and proliferation. These findings suggest that tailored magnetized silk-based biomaterials can be engineered with interesting features for biomaterials and tissue-engineering applications

Multilayered magnetic gelatin membrane scaffolds

A versatile approach for the design and fabrication of multilayer magnetic scaffolds with tunable magnetic gradients is described. Multilayer magnetic gelatin membrane scaffolds with intrinsic magnetic gradients were designed to encapsulate magnetized bioagents under an externally applied magnetic field for use in magnetic-field-assisted tissue engineering. The temperature of the individual membranes increased up to 43.7 degrees C under an applied oscillating magnetic field for 70 s by magnetic hyperthermia, enabling the possibility of inducing a thermal gradient inside the final 3D multilayer magnetic scaffolds. On the basis of finite element method simulations, magnetic gelatin membranes with different concentrations of magnetic nanoparticles were assembled into 3D multilayered scaffolds. A magnetic-gradient-controlled distribution of magnetically labeled stem cells was demonstrated in vitro. This magnetic biomaterial-magnetic cell strategy can be expanded to a number of different magnetic biomaterials for various tissue engineering applications