Materials Science and Engineering Commons^™

Magnetic Properties Of Nd-Fe-B Permanent Magnets Under Thermal Experimentation, Géraldine Houis

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Neodymium-Iron-Boron (Nd-Fe-B) magnets were developed in the 1980s, and since then, they have appeared as a common component in many fields. From the industry to consumers or defense applications, from turbines, computers, cellphones to most audio systems, Nd-Fe-B magnets are present everywhere. But when Nd-Fe-B magnets are applied to the motors of electric vehicles and wind-turbine generators, their temperature rises, therefore Nd-Fe-B-Dy magnets are used. However, while the use of these magnets is common at low temperatures, their properties decrease dramatically with the increase of temperature. In this paper, the Nd-Fe-B-based samples used were prepared by using arc melting, melt …

Structural, Magnetic And Microstructural Studies Of Composition-Modified Sm-Co Ribbons, Xiujuan Jiang

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

There is an increasing interest in developing desirable microstructures in hard magnetic materials. Sm-Co-based magnets, bearing superior intrinsic magnetic properties, are good candidates for further development. Two Sm-Co-based alloys, (Sm₁₂Co₈₈)_100-x-yCr_yC_x (taking SmCo₇ phase) and SmCo_4-xFe_xB (a derivative of SmCo₅ phase), were produced using melt-spinning technique. The magnetic properties are correlated to the structural and microstructural properties.

Within the SmCo₇ stoichiometry, cumulative effects of Cr and C additions on the structural and magnetic properties have been investigated. Experimental results have shown that these additions along …

Domain-Wall Pinning At Inhomogenities Of Arbitrary Cross-Sectional Geometry, Ralph Skomski, Jian Zhou, Arti Kashyap, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

Abstract—The coercivity of cellular Sm-Co based permanent magnets is investigated by model calculations. The grain boundaries responsible for the pinning coercivity are modeled as planar inhomogenities with arbitrary cross-sectional geometry. The calculation yields a physically transparent integral equation for the pinning energy, whose derivative is the pinning force. The theory rationalizes experimental data on a semiquantitative level, but without adjustable parameters, and bridges the gap between smooth concentration gradients and abrupt interfaces. Explicit results are obtained for sinoidal profiles, for very thin grain boundaries, and for profiles intermediate between attractive and repulsive pinning. The corrections predicted by the present model …

Finite-Temperature Anisotropy Of Ptco Magnets, Ralph Skomski, Arti Kashyap, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

The temperature dependence of the magnetocrystalline anisotropy of PtCo and its atomic origin are investigated by first-principle and model calculations. The Pt spin moment necessary to realize the leading 5d anisotropy contribution is due to neighboring Co atoms. At finite temperatures, Co spin disorder strongly reduces the Pt moment and the anisotropy. This is in contrast to the situation encountered in 3d and 3d–4f magnets, where the atomic magnetic moments remain largely conserved, even above the Curie temperature. A consequence of the L1₀ mechanism is that theK₁ (T) curve of exhibits a negative curvature, in contrast to the …

Exchange Interactions And Curie Temperature Of Y–Co Compounds, Arti Kashyap, Ralph Skomski, Renat F. Sabiryanov, Sitaram Jaswal, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

The Curie temperature of rare-earth Co intermetallics is investigated by self-consistent spin-polarized electronic-structure calculations on Y–Co compounds. The total exchange interaction of a given site with all other sites (J_o) is calculated by the linear-muffin-tin-orbital method using the local force theorem and employed to obtain mean-field Curie-temperature estimates. The theoretical predictions for YCo₃, YCo₅, and Y₂Co₁₇ are in fair agreement with the experimental Curie temperatures. For YCo₅, the variation of exchange interactions (J_ij) with distance is analyzed, and it is discussed how the presence of nonequivalent cobalt …