Model for Calculating J(H) Curves of Ni Coated Nd-Fe-B Magnets |
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| Affiliation: | 1. School of Mechatronics, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro, Buk-gu, Gwangju 500-712, Republic of Korea;2. Home Appliance Laboratory, LG Electronics Inc., Seoul, Republic of Korea;1. School of Electronic and Electrical Engineering and Sungkyunkwan Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 440-746, Republic of Korea;2. Department of Physics, Sogang University, Seoul 121-742, Republic of Korea;3. Nanomaterials Research Group, Physics Division, PINSTECH, Nilore, Islamabad, Pakistan;4. Department of Physics, COMSATS Institute of Information Technology, Lahore 54000, Pakistan;1. Université de Carthage, Faculté des Sciences de Bizerte, UR11ES30, Synthèse et Structures de Nanomatériaux, 7021 Jarzouna, Tunisia;2. Université de Toulouse, LPCNO, INSA CNRS UMR 5215, 135 av. de Rangueil, 31077 Toulouse Cedex 4, France;3. Northern Borders University, College of Sciences, Arar, Saudi Arabia;4. Université de Tunis el Manar, Faculté des Sciences de Tunis, Campus Universitaire, 2092, El Manar, Tunis;1. Physics and Materials Science Research Unit, University of Luxembourg, 162A Avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg;2. Bragg Institute, ANSTO, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia;1. NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland;2. Departament de Física Aplicada i Òptica, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain |
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| Abstract: | An analytical model to describe the influence of surface degradation and the Ni layer itself on the magnetic properties of Ni coated Nd-Fe-B magnets is presented. Starting from the bulk magnetic properties, the dimensions, the thickness of Ni coating and the affected surface layer, J(H) demagnetization curve is calculated. Subsequently the expected values of (BH)max, and the reversible permeability are deduced from the calculated J(H) curves. For flat magnets the surface effects lead to a decrease of Br and an increase of the permeability which lowers (BH)max. For strait magnets a step in the J(H) curve appears at H = 0. The deteriorating effect of Ni coating and the surface layer scale with the dimensions of magnet and the thickness of these layers, which depend on the processing and the grain size of magnet. These effects can not be neglected if one or more dimensions of a Ni coated magnet are less than about 5 mm. SmCo5 magnets show similar effects but the coercivity of the damaged surface layer is higher. Pinning type Sm2Co17 magnets show almost no deterioration on surface due to machining. As a result, Sm-Co magnets are better suited for applications with dimensions smaller than about 2 mm. |
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