Unraveling Nanostructured Spin Textures in Bulk Magnets

One of the key challenges in magnetism remains the determination of the nanoscopic magnetization profile within the volume of thick samples, such as permanent ferromagnets. Thanks to the large penetration depth of neutrons, magnetic small-angle neutron scattering (SANS) is a powerful technique to characterize bulk samples. The major challenge regarding magnetic SANS is accessing the real-space magnetization vector field from the reciprocal scattering data. In this letter, a fast iterative algorithm is introduced that allows one to extract the underlying two-dimensional magnetic correlation functions from the scattering patterns. This approach is used here to analyze the magnetic microstructure of Nanoperm, a nanocrystalline alloy which is widely used in power electronics due to its extraordinary soft magnetic properties. It can be shown that the computed correlation functions clearly reflect the projection of the three-dimensional magnetization vector field onto the detector plane, which demonstrates that the used methodology can be applied to probe directly spin-textures within bulk samples with nanometer-resolution.Comment: 9 pages, 3 figure

Hydrothermal synthesis, characterization, and magnetic properties of cobalt chromite nanoparticle

The CoCr2O4 nanoparticles were prepared by hydrothermal treatment of chromium and cobalt oleates in a mixture of solvents (water and ethanol or pentanol) at various temperatures. The samples were further annealed at the temperatures from 300 to 500 C. The obtained nanoparticles were characterized using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), high-resolution TEM, scanning electron microscopy, thermogravimetric analysis, Raman and infrared spectroscopy, and magnetic measurements. The particle size, ranging from 4.4 to 11.5 nm, was determined from the TEM and PXRD methods. The tendency of particles to form the aggregates with the increasing annealing temperature has been observed. The magnetic measurements revealed that the typical features of the CoCr 2O4 long-range magnetic order are suppressed in the nanoparticles

Critical size limits for collinear and spin-spiral magnetism in CoCr_2\mathrmO_4

The multiferroic behavior of CoCr2O4 results from the appearance of conical spin-spiral magnetic ordering, which induces electric polarization. The magnetic ground state has a complex size-dependent behavior, which collapses when reaching a critical particle size. Here the magnetic phase stability of CoCr2O4 in the size range of 3.6–14.0 nm is presented in detail using the combination of neutron diffraction with XYZ polarization analysis and macroscopic magnetization measurements. We establish critical coherent domain sizes for the formation of the spin spiral and ferrimagnetic structure and reveal the evolution of the incommensurate spin spiral vector with particle size. We further confirm the presence of ferroelectric polarization in the spin spiral phase for nanocrystalline CoCr2O4