3.19.4
The magnitude of the field required is dependent on the coercive field of the material. Virtually all magnet producers and suppliers provide this data.The coercive field is a measure of how difficult it is to both magnetize and demagnetize the magnet. The higher the coercive field of the magnet, the more difficult it is to magnetize. Table 3.22 indicates the range of coercive field values for different types of magnets. A rule of thumb is that the applied field should be 1M to 4 times the coercive force of the magnetic material. The coercive force of high-energy materials may reach 15,000 Oe or more; therefore, magnetic fields of more than 50,000 Oe may be required to reach magnetic saturation. The magnetic fields in a fixture can be measured using either a gaussmeter or a fluxmeter.
TABLE 3.22 Magnetizing Force Required for Saturation of Common Commercial Magnets
| Decade | Coercivity, | Magnetizing | Resistivity, | |
| Material | introduced | Oe | field,Oe | Q- cm |
| Alnico | 1940s | 500-1,500 | 1,500-5,000 | 50 |
| Ferrite | 1950s | 2,300-4,000 | 5,000-10,000 | 1 x 106 |
| SmCo | 1970s | 6,000-20,000 | 6,000-50,000 | 53 |
| NdFeB | 1980s | 11,000-25,000 | 15,000-50,000 | 150 |
