Spin canting across core/shell Fe3O4/MnxFe3−xO4 nanoparticles

Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like magnetic imaging and hyperthermia based cancer treatment. Understanding their magnetic spin configurations is important for optimizing these applications. The measured magnetization of MNPs can be significantly lower than bulk counterparts, often due to canted spins. This has previously been presumed to be a surface effect, where reduced exchange allows spins closest to the nanoparticle surface to deviate locally from collinear structures. We demonstrate that intraparticle effects can induce spin canting throughout a MNP via the Dzyaloshinskii-Moriya interaction (DMI). We study ~7.4 nm diameter, core/shell Fe3O4/MnxFe3−xO4 MNPs with a 0.5 nm Mn-ferrite shell. Mössbauer spectroscopy, x-ray absorption spectroscopy and x-ray magnetic circular dichroism are used to determine chemical structure of core and shell. Polarized small angle neutron scattering shows parallel and perpendicular magnetic correlations, suggesting multiparticle coherent spin canting in an applied field. Atomistic simulations reveal the underlying mechanism of the observed spin canting. These show that strong DMI can lead to magnetic frustration within the shell and cause canting of the net particle moment. These results illuminate how core/shell nanoparticle systems can be engineered for spin canting across the whole of the particle, rather than solely at the surface

Modulation of diffusion with polarized lasers

Laser diffusion is generally used to modify the metallurgical composition at the surface of materials for improving the mechanical properties. Platinum has been diffused into titanium and tantalum sheets in this study, and the concentrations of Pt in the substrates are determined. The concentration of Pt is higher at lower scanning speeds due to higher surface temperature and longer diffusion time than in the case of higher scanning speeds. Additionally, the samples treated with a linearly polarized laser beam exhibit slightly higher concentration of Pt. The enhanced diffusion in the case of linearly polarized laser treatment can be attributed to controlled excitation of the local vibration modes of the atoms in the substrate. The reflectivity of the samples are also measured at the wavelength of 1,064 nm and compared with theoretical results. © 2014 Springer-Verlag Berlin Heidelberg