Hans Marc Bert Boeve

Human erythrocytes as nanoparticle carriers for magnetic particle imaging

The potential of red blood cells (RBCs) loaded with iron oxide nanoparticles as a tracer material for magnetic particle imaging (MPI) has been investigated. MPI is an emerging, quantitative medical imaging modality which holds promise in terms of sensitivity in combination with spatial and temporal resolution. Steady-state and dynamic magnetization measurements, supported by semi-empirical modeling, were employed to analyze the MPI signal generation using RBCs as novel biomimetic constructs. Since the superparamagnetic iron oxide (SPIO) bulk material that is used in this study contains nanoparticles with different sizes, it is suggested that during the RBC loading procedure, a preferential entrapment of nanoparticles with hydrodynamic diameter ≤60 nm occurs by size-selection through the erythrocyte membrane pores. This affects the MPI signal of an erythrocyte-based tracer, compared to bulk. The reduced signal is counterbalanced by a higher in vivo stability of the SPIO-loaded RBCs constructs for MPI applications.

Reduction of Ne/spl acute/el coupling in magnetic tunnel junctions containing an artificial ferrimagnet in the free layer

Magnetic tunnel junctions containing an artificial ferrimagnet (AFi) in the free layer are investigated. A lower offset field for the free layer is found compared to tunnel junctions with a single free layer of equal net magnetic moment. A reduction in Ne/spl acute/el coupling up to 36% is achieved. The Ne/spl acute/el coupling is interpreted in terms of the roughness parameters of the tunnel barrier. The combination of an AFi in the free layer with a robust exchange-biased hard layer, including an artificial antiferromagnet, leads to even lower values for the offset field. The sign of the offset field depends on the order of the layers inside the (free) AFi. The coupling strength of the AFi is further investigated in terms of layer thicknesses.

Oxygen-mediated Mn diffusion in magnetic tunnel junctions comprising a nano-oxide layer

Mn diffusion toward the tunnel barrier in the hard layer system of a magnetic tunnel junction is recognized as the limitation for the temperature stability. In a series of experiments, a nano-oxide layer (NOL) was included into the hard layer as a diffusion barrier. The tunnel magnetoresistance (TMR) ratio has been monitored and interpreted as a function of anneal temperature, in combination with Auger analysis. At elevated anneal temperature, a more pronounced TMR decay was observed that originates in a different diffusion mechanism for Mn atoms, compared to tunnel junctions without NOL.