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Balamurugan, B.

Publications and source records attributed to Balamurugan, B..

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Structural and magnetic properties of Co-V nanoparticles

We have investigated the structural and magnetic properties of Co 1-x V x nanoparticles (NPs) with composition x = 0.25 (stoichiometric) and 0.29 (under-stoichiometric) prepared by the cluster-beam deposition (CBD) technique. Our data shows that the as-made Co 1-x V x NPs are a mixture of the high-temperature phase (HTP) and the low-temperature phase (LTP) of Co 3 V and the particles are superparamagnetic at room temperature (RT) with blocking temperatures (T B ) of 90 and 137 K for x = 0.25 and 0.29, respectively. This behavior contrasts with the bulk which are paramagnetic down to 4.2 K. When the Co 75 V 25 NPs are annealed at 573 K, they undergo a phase separation into a mixture of phases and become ferromagnetic at room temperature with Curie temperature (T c ) of 515 K.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Boundary conditions and Berry phase in magnetic nanostructures

The effect of micromagnetic boundary conditions on the Berry curvature and topological Hall effect in granular nanostructures is investigated by model calculations. Both free surfaces and grain boundaries between interacting particles or grains affect the spin structure. The Dzyaloshinskii-Moriya interactions yield corrections to the Erdmann-Weierstrass boundary conditions, but the Berry curvature remains an exclusive functional of the local spin structure, which greatly simplifies the treatment of nanostructures. An explicit example is a model nanostructure with cylindrical symmetry whose spin structure is described by Bessel function and which yields a mean-field-type Hall-effect contribution that can be related to magnetic-force-microscopy images.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Ferromagnetism in Laves-phase WFe{sub 2} nanoparticles

While rare-earth based Laves phases are known to exhibit large magnetostriction, the magnetic properties of some binary Laves phases containing transition metals alone are not well known. This is because many of these compounds contain refractory elements that complicate melt processing due to high melting temperatures and extensive phase separation. Here, phase-pure WFe{sub 2} nanoclusters, with the hexagonal C14 Laves structure, were deposited via inert gas condensation, allowing for the first known measurement of ferromagnetism in this phase, with M{sub S} of 26.4 emu/g (346 emu/cm{sup 3}) and a K{sub U} of 286 kerg/cm{sup 3}, at 10 K, and a T{sub C} of 550 K.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Novel structures and physics of nanomagnets (invited)

Nanoscale magnets with characteristic dimensions in the range of 1–100 nm are important in several areas of nanoscience and technology. First, this length scale spans the typical important dimensions of exchange lengths and domain-wall widths, which means that significant control of magnetic properties can be obtained by varying grain or particle dimensions. Second, the nonequilibrium synthetic processes used for clusters, particles, and films, often lead to new real-space crystal structures with completely novel spin structures and magnetic properties. Third, a basic-science challenge in this class of matter involves the spin-polarized quantum mechanics of many-electron systems containing 10–10 000 atoms. Finally, the materials under study may have important future applications in high-density data storage, ultra-small spintronic devices, or high-energy magnetic materials. In this article, we discuss our recent work on novel Fe-Au nanoclusters, MnAu-Mn core-shell structures, and complex high-anisotropy Co-rich intermetallic compound clusters. We also present new results on Fe-based alloys including the magnetic properties of semiconducting FeSi{sub 2} nanoclusters and spin correlations in FeGe nanocluster films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Spin-modified catalysis

First-principle calculations are used to explore the use of magnetic degrees of freedom in catalysis. We use the Vienna Ab-Initio Simulation Package to investigate both L1{sub 0}-ordered FePt and CoPt bulk materials and perform supercell calculations for FePt nanoclusters containing 43 atoms. As the catalytic activity of transition-metal elements and alloys involves individual d levels, magnetic alloying strongly affects the catalytic performance, because it leads to shifts in the local densities of states and to additional peaks due to magnetic-moment formation. The peak shift persists in nanoparticles but is surface-site specific and therefore depends on cluster size. Our research indicates that small modifications in stoichiometry and cluster size are a useful tool in the search for new catalysts.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗