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1993

Ralph Skomski Publications

Articles 1 - 9 of 9

Full-Text Articles in Physics

Giant Energy Product In Nanostructured Two-Phase Magnets , Ralph Skomski, J.M.D. Coey Dec 1993

Giant Energy Product In Nanostructured Two-Phase Magnets , Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

Exchange hardening of nanostructured two-phase systems composed of an aligned hard phase and a soft phase with high magnetization is investigated using an approach which yields analytic nucleation fields from the micromagnetic vector equation, and accounts for interactions between the soft regions. In suitable structures the nucleation field is proportional to the volume-averaged anisotropy constant. For example, a multilayer composed of alternating 2.4 nm hard-magnetic Sm2Fe17N3 layers and 9 nm Fe65Co35 layers can have an energy product as high as 1 MJ/m3 (120 MG Oe), with a rare-earth content ...


Nucleation Field And Energy Product Of Aligned Two-Phase Magnets - Progress Towards The '1 Mj/M3' Magnet, Ralph Skomski, J.M.D. Coey Nov 1993

Nucleation Field And Energy Product Of Aligned Two-Phase Magnets - Progress Towards The '1 Mj/M3' Magnet, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

Exchange hardening of nanostructured two-phase systems composed of an aligned hard phase and a soft phase with high magnetization is investigated using a micromagnetic approach which accounts for interactions between the soft regions. For Sm2Fe17N3 (2.5 nm)/Fe65Co35 (9 nm) multilayers an energy product as high as 1 MJ/m3 (120 MCOe) is predicted, witb a rare-earth content of only 5 wt %. Giant energy products may also be achieved in suitable cellular and disordered structures.


Nitrogen Diffusion In Sm2Fe17 And Local Elastic And Magnetic Properties, Ralph Skomski, J.M.D. Coey Jun 1993

Nitrogen Diffusion In Sm2Fe17 And Local Elastic And Magnetic Properties, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

The reaction between nitrogen gas and an intermetallic compound is studied, with particular reference to Sm2Fe17, treating the Sm2Fe17Ny, system as a gas-solid solution. A simple lattice gas model is used to describe the reaction of nitrogen atoms with the metal lattice in terms of the net reaction energy U0= - 57 ± 5 kJ/mol. The equilibrium nitrogen concentration is calculated as a function of nitrogenation temperature and gas pressure. Refined diffusion parameters D0= 1.02 mm2/s and Ea= 133 kJ/mol, determined by thermopiezic analysis of the ...


Crystal Field In Nitrogenated Rare-Earth Intermetallics, Ralph Skomski, M.D. Kuz'min, J.M.D. Coey May 1993

Crystal Field In Nitrogenated Rare-Earth Intermetallics, Ralph Skomski, M.D. Kuz'min, J.M.D. Coey

Ralph Skomski Publications

The crystal-field in Sm2Fe17N3- δ and Sm(Fe11Ti)N1- δ due to interstitial nitrogen has been investigated. Intrinsic parametrization in the superposition model allows separation of the crystal field created by a neighboring nitrogen atom from a purely geometrical factor, which is different for Sm2Fe17N3- δ and Sm( Fe11Ti) N1- δ Using published magnetic data, values for the intrinsic parameter A2 per nitrogen atom of A2=200± 60 Ka0-2 and A2=270±60 Ka0-2 for Sm2 ...


Characterization, Transport, And Magnetic Properties Of Co/Pd Multilayers Produced By Pulsed Laser Deposition, M. Enrech, Ralph Skomski, J.M.D. Coey, J.G. Lunney May 1993

Characterization, Transport, And Magnetic Properties Of Co/Pd Multilayers Produced By Pulsed Laser Deposition, M. Enrech, Ralph Skomski, J.M.D. Coey, J.G. Lunney

Ralph Skomski Publications

Metallic Co/Pd multilayers with equal layer thickness and periods ranging from 5 to 150 A were deposited using pulsed laser deposition. They have an fcc (111) texture and the diffraction patterns give clear evidence of a modulated period structure. From the period dependence of the in-plane electrical resistivity a diffuse interface between cobalt and palladium of thickness b= 6 ± 2 Å has been deduced. Magnetic, magnetoresistance, and Kerr-effect measurements indicate in-plane magnetization. In low fields (B0 < 10 mT) the magnetoresistanceis highly anisotropic, varying by ~2% in the transverse configuration and + 1% in the longitudinal configuration due to orbital moment of cobalt in the interface region. The shape of the Kerr-effect major hysteresis loop can be explained by the in-plane component of the anisotropy of the cobalt layers.


On The Role Of Zn In Sm2Fe17NX Permanent Magnets, P.A.P. Wendhausen, D. Eckert, A. Handstein, K.-H. Müller, G. Leitner, Ralph Skomski May 1993

On The Role Of Zn In Sm2Fe17NX Permanent Magnets, P.A.P. Wendhausen, D. Eckert, A. Handstein, K.-H. Müller, G. Leitner, Ralph Skomski

Ralph Skomski Publications

Coercivities up to 1.9 T were achieved by bonding micron-size Sm2Fe17Nx particles with zinc. X-ray analysis of Zn-bonded samples indicates the presence of the ZnFe Γ phase and no unreacted Zn, after heat treatment at about 390 °C for 100 min for samples with Zn content varying from 5 to 35 wt. %. The increase of coercivity occurs only for a more intense heat treatment, e.g., at 390 °C! for 300 min or 425 °C for 100 min. Differential scanning calorimetry (DSC) shows two exothermic peaks at 388 and 426 °C, but no endothermic ...


Interstitial Modification Of Rare-Earth Intermetallics, Ralph Skomski, S. Murray, S. Brennan, J.M.D. Coey May 1993

Interstitial Modification Of Rare-Earth Intermetallics, Ralph Skomski, S. Murray, S. Brennan, J.M.D. Coey

Ralph Skomski Publications

Interstitial modification of R2Fe17Zx is studied with R=Y, Sm, and Z=N, C, B, Si, and S. Equilibrium interstitial concentrations are calculated using a lattice gas model. For gas-solid reaction a low solubility is obtained at high temperatures, whereas a solid-solid reaction is predicted to yield R2Fe17Z1.5 in the high-temperature limit. Theoretical results are compared with data on Sm2Fe17Cx produced by solid-solid reaction at 500 °C. Volume expansions up to 4.8% were obtained, which corresponds to x≈2. The concentrations of interstitial ...


Magnetic Reversal In Sm2Fe17NY Permanent Magnets, Ralph Skomski, K.-H. Müller, P.A.P. Wendhausen, J.M.D. Coey May 1993

Magnetic Reversal In Sm2Fe17NY Permanent Magnets, Ralph Skomski, K.-H. Müller, P.A.P. Wendhausen, J.M.D. Coey

Ralph Skomski Publications

Coercivity and nucleation fields for three-dimensional inhomogenities are calculated and discussed. For soft spherical inclusions in a hard magnetic matrix a (δ /R) 2 dependence of the nucleation field on inclusion radius R and domain wall width δ has been obtained. To calculate propagation fields for spherical inhomogenities, a nonlinear model has been used. The corresponding coercive field can be much higher than the nucleation field, particularly if the magnitude of the anisotropy changes very steeply. Soft inclusions with sharp interfaces are ineffective at producing complete magnetic reversal. For partly nitrided particles coercivity and nucleation field are predicted to be ...


New Magnets From Interstitial Intermetallics, J.M.D. Coey, Ralph Skomski Apr 1993

New Magnets From Interstitial Intermetallics, J.M.D. Coey, Ralph Skomski

Ralph Skomski Publications

The outlook for improving the energy product of permanent magnets beyond the theoretical limit of 516 kJ/m3 for Nd2Fe14B is discussed. Most promising are nanostructured two-phase magnets consisting of an aligned hard-magnetic skeleton phase possessing exceptionally high uniaxial anisotropy and a soft-magnetic phase which assures a high magnetization. Brown’s paradox is discussed for inhomogeneous magnets, and micromagnetic calculations are used to predict energy products as high as 1090 kJ/m3 in suitable nanostructured Sm2Fe17N3/Fe65Co35 composites, such as multilayers or disordered two-phase magnets with common ...