Model Calculation of Magnetization Reversal Process of Hard Magnet in Nd2Fe14B System
We propose a mechanism that exhibits the coercivity reduction of Nd--Fe--B magnets. The model employed here is a micromagnetic model involving the anisotropy- and exchange-fields obtained by using first-principles calculations. The uniqueness of this model is that it has a $c$-plane magnetic anisotr...
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| Published in | Applied physics express Vol. 4; no. 11; pp. 113002 - 113002-3 |
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| Main Authors | , , |
| Format | Journal Article |
| Language | English |
| Published |
The Japan Society of Applied Physics
01.11.2011
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| Online Access | Get full text |
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| Summary: | We propose a mechanism that exhibits the coercivity reduction of Nd--Fe--B magnets. The model employed here is a micromagnetic model involving the anisotropy- and exchange-fields obtained by using first-principles calculations. The uniqueness of this model is that it has a $c$-plane magnetic anisotropy around its surface, in contrast to the bulk $c$-axis anisotropy. We find that the local $c$-plane anisotropy drastically affects the coercivity, resulting in a reduction by half of the bulk anisotropy field $H_{k}$. We also find that partial substitution of Dy for Nd around the surface actually recovers the coercivity. |
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| Bibliography: | Crystal structure of an $R_{2}$Fe 14 B compound (left) and SC lattice model for the calculation of the $R$ ions (right). The calculation is carried out on $4\times 4\times 100$ lattice points. Shown is a partial configuration. Calculated magnetization loops of the SC model. The surface anisotropy values are $K_{\text{S}}=D$, 0, $-0.5D$, and $-1.0D$, where $D=4.8\times 10^{7}$ erg/cm 3 . Dependence of $H_{\text{c}}$ as a function of the Dy layer thickness. Open squares and filled circles represent the cases for the exchange parameter $J_{\text{ex}}=4.8$ and 9.6 meV, respectively. Time evolution of magnetic moments in the SC model. (a) Dy layer exists only on the surface of the magnet, and (b) Dy layer is 5% of the total thickness. In both (a) and (b), the right edge of the picture corresponds to the surface of the magnet. |
| ISSN: | 1882-0778 1882-0786 |
| DOI: | 10.1143/APEX.4.113002 |