Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

1994

Ralph Skomski Publications

Articles 1 - 5 of 5

Full-Text Articles in Physics

Aligned Two-Phase Magnets: Permanent Magnetism Of The Future? (Invited), Ralph Skomski Nov 1994

Aligned Two-Phase Magnets: Permanent Magnetism Of The Future? (Invited), Ralph Skomski

Ralph Skomski Publications

Micromagnetic calculations are used to investigate coercivity and energy products of magnets consisting of an aligned hard-magnetic skeleton phase and a soft-magnetic phase with high saturation magnetization. Compared to the present-day theoretical limit of 516 W/m3 for single-phase Nd2Fe14B, the energy product in suitable nanostructured Sm2Fe2N3/Fe65Co35 composites is predicted to be as high as 1090 kJ/m3. The influence of the skeleton’s texture and shape is discussed, and aligned nanocrystalline two-phase magnets are compared with remanence-enhanced isotropic magnets. In particular, it is shown how ...


Magnetoresistance In Nanostructured Co-Ag Prepared By Mechanical- Alloying, J.M.D. Coey, A.J. Fagan, Ralph Skomski, J. Gregg, K. Ounadjela, S.M. Thompson Mar 1994

Magnetoresistance In Nanostructured Co-Ag Prepared By Mechanical- Alloying, J.M.D. Coey, A.J. Fagan, Ralph Skomski, J. Gregg, K. Ounadjela, S.M. Thompson

Ralph Skomski Publications

Fine cobalt and silver powders have been ball-milled to yield a granular solid of composition Co30Ag70 in the form of coarse powder. The material is an intimate mixture of grains of fcc CO in a silver matrix. The cobalt is in the single-domain size range, and the samples exhibit coercivity (0.07 T at 296 K) and unusual thermomagnetic effects, including field-induced unidirectional anisotropy. There is a large, isotropic negative magnetoresistance, which exceeds 10 95 at 4.2 K.


Non-Equilibrium Gas-Phase Nitrogenation, S. Brennan, Ralph Skomski, J.M.D. Coey Mar 1994

Non-Equilibrium Gas-Phase Nitrogenation, S. Brennan, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

Non-equilibrium nitrogenation of transition-metal rich rare-earth intermetallics can be used to increase the nitrogen content beyond its equilibrium concentration. For example, nitrogenation of Sm2Fe17 using ammonia yields volume expansions up to 8.3 vol %, which correspond to a composition Sm2Fe17Nx with x = 4. This effect is related to catalytic action at the metal surface where ammonia is decomposed into nitrogen and hydrogen, with nitrogen absorption on a site where it is weakly bound, as an intermediate step. For overloaded Sm2Fe17Nx with x>3 the net reaction energy ...


Exchange Coupling And Energy Product In Random Two- Phase Aligned Magnets, Ralph Skomski, J.M.D. Coey Mar 1994

Exchange Coupling And Energy Product In Random Two- Phase Aligned Magnets, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

Size effects in two-phase Boolean magnets composed of an aligned hard phase and a soft phase with high magnetization are investigated. In 'over-critical' magnets, where the size of the soft regions is larger than the Blochwall width δh of the hard phase, the energy product is reduced compared to the corresponding 'undercritical' magnets with small soft regions, where theoretical energy products as high as 1 M J / m3 have been predicted. Nevertheless, the theoretical energy product only gradually drops with increasing size of the soft regions, and it may still exceed the theoretical energy product 516 kJ/m ...


Magnetoresistance In Nanostructured Co-Ag Prepared By Mechanical- Alloying, J.M.D. Coey, A.J. Fagan, Ralph Skomski, J. Gregg, K. Ounadjela, S.M. Thompson Mar 1994

Magnetoresistance In Nanostructured Co-Ag Prepared By Mechanical- Alloying, J.M.D. Coey, A.J. Fagan, Ralph Skomski, J. Gregg, K. Ounadjela, S.M. Thompson

Ralph Skomski Publications

Fine cobalt and silver powders have been ball-milled to yield a granular solid of composition Co30Ag70 in the form of coarse powder. The material is an intimate mixture of grains of fcc CO in a silver matrix. The cobalt is in the single-domain size range, and the samples exhibit coercivity (0.07 T at 296 K) and unusual thermomagnetic effects, including field-induced unidirectional anisotropy. There is a large, isotropic negative magnetoresistance, which exceeds 10 % at 4.2 K.