Strong and Inhomogeneous Magnetic Fields Sources Based on High Anisotropy Rare-Earth Permanent Magnets

摘要

We studied the systems of permanent magnets in which strong magnetic stray fields occurred. Basing on calculations and direct experiments it was shown that magnetic fields exceeding several times the induction of magnet material could be produced by permanent magnets with very high magnetic anisotropy (the anisotropy field H_K 4πM_S). These fields are localized in the narrow region in the vicinity of the points near the edges of uniformly charged surfaces of the magnetic system. The dimension of the region depends on the extent of the surface where the magnetization is uniform (a) and equals ≈0.1a. It was found that both the giant magnetic anisotropy of the magnet material, which guarantees the permanency of the direction of the uniform magnetization, and high coercivity are necessary conditions for producing of strong magnetic fields. The occurring strong stray fields are high-gradient, the magnitude of H▽H can reach ≈(10~7)/(10~(11))Oe~2/cm. The estimates of limiting attainable fields and their gradients are made. It was shown that for half-opened system of magnets (A) the limiting field could not exceed the values 10~5Oe, and ▽H < 10~9 Oe/cm. Summing up it is necessary to note the following. Using the considered approaches of the design and rare-earth magnets with giant anisotropy assured by optimal structure of these materials, our developments of other sources of strong and high-gradient magnetic fields for various assignments are in progress.