A recent experiment determined the magnetic moment /Mn, M, in the dilute MnxSi1-x with x = 0.1% to be 5.0 µB/Mn.
The existing calculated M values range from 2.37 to 3.1µB/Mn except the case with a fixed charge state, Mn2+, which
gives 5.0µB/Mn. We address the issue: Can a single Mn at its neutral charge state in dilute MnxSi1-x alloys have M = 5.0
µB/Mn? After carrying out extensive calculations, the only model giving this M value involves a supercell having a total
of 513 atoms with a Mn at a substitutional site and a Si at a tetrahedral interstitial site serving as a second neighbor to the
Mn. Physically, the Mn contributes 4.0 µB due to the weakening of the d-p hybridization between the transition metal
element and its nearest neighbor Si caused by the presence of the second neighbor Si. The additional 1.0 µB is the
consequence of the exchange interaction through the remaining weak overlap of the wave functions between the d-state
of the Mn and the sp3 state of the nearest neighbor Si atom. Evidences for the weakening of the d-p hybridization are
Multilayered magnetic nanowires provide ideal platforms for nanomagnetism and spin-transport studies. They exhibit complex magnetization reversal behaviors as dimensions of the magnetic components are varied, which are difficult to probe since the magnetic entities are buried inside the nanowires. We have captured magnetic and magnetoresistance "fingerprints" of Co nanodiscs in Co/Cu multilayered nanowires as they undergo a single domain to vortex state transition, using a first-order reversal curve (FORC) method. The Co/Cu multilayered nanowires have been synthesized by pulsed electrodeposition into nanoporous polycarbonate membranes. In 50 nm diameter nanowires of [Co(5nm)/Cu(8nm)]400, a 10% magnetoresistance effect is observed at 300 K. In 200 nm diameter nanowires, the magnetic configurations can be tuned by adjusting the Co nanodisc aspect ratio. The thinnest nanodiscs exhibit single domain behavior. The thicker ones exhibit vortex states, where the nucleation and annihilation of the vortices are manifested as butterfly-like features in the FORC distributions. The magnetoresistance effect shows different characteristics, which correspond to the different magnetic configurations of the Co nanodiscs.
Many types of fluorescent nanoparticles have been investigated as alternatives to conventional organic dyes in biochemistry. In addition, magnetic beads are another type of particle that have a long history of biological applications. In this work we apply flame spray pyrolysis in order to engineer a novel type of nanoparticle that has both luminescent and magnetic properties. The particles have magnetic cores of iron oxide doped with cobalt and neodymium and luminescent shells of europium-doped gadolinium oxide (Eu:Gd2O3). Measurements on a Vibrating Sample Magnetometer showed an overall paramagnetic response of these composite particles. Fluorescence spectroscopy showed spectra typical of the Eu ion in a Gd2O3 host; a narrow emission peak centered near 615 nm. Our synthesis method offers low-cost, high-rate synthesis allowing a wide range of biological applications of magnetic/fluorescent core/shell particles. We demonstrate an immunoassay using the magnetic and fluorescent properties of the particles for separation and detection purposes.