Sintered neodymium magnet, as the name implies, is a compound Nd2Fe14B composed of three elements: neodymium Nd, iron Fe, and boron B. It is an alloy material based on the matrix. However, sintered neodymium magnet is not a single phase, but is composed of Nd2Fe14B phase and Nd-rich phase (also known as rare-earth-rich phase), of which Nd2Fe14B phase is the main phase or basic term.
Most rare earth elements (RE) form RE 2Fe14B compounds, which are the basic phase of sintered rare earth iron boron permanent magnet materials, accounting for 96%-98% of sintered rare earth iron boron permanent magnets. All RE 2Fe14B compounds have the same crystal structure, but their magnetic properties are very different. That is to say, adding other rare earth elements to sintered NdFeB to replace neodymium can change some properties of the magnet.
The role of heavy rare earth metal Tb instead of Nd
Adding Tb to the sintered neodymium magnet to partially replace Nd has the same effect as the replacement of Nd by Dy, but the anisotropic field HA of Tb 2Fe14B is higher, so it can more effectively improve the coercivity of the permanent magnet. But Tb has less reserves in rare earth mines than Dy, and the price is higher.
The role of heavy rare earth metal Dy instead of Nd
1. Significantly improve the coercivity of the magnet
2. Reduce the magnetic polarization intensity Js of the magnet, thereby reducing the remanence Br and the maximum magnetic energy product (BH) m
3. Reduce the temperature coefficient of magnet remanence Br and maximum magnetic energy product (BH) m
The role of metal Gd and metal Ho replacing Nd
Among the heavy rare earth metals, Gd has the highest reserves, and Gd can also form Gd2Fe14B compounds. The magnetic polarization intensity Js and anisotropic field HA of this compound are obviously lower, but its Curie temperature Tc is the highest. Due to the high reserves of Gd and the low price, some manufacturers add Gd in the form of gadolinium-iron alloy to partially replace Nd to produce low-cost sintered NdFeB. However, its practical use of Gd to replace Nd is a waste. Once it is discovered that Gd has more important uses in the future, it will be found to be an irreversible loss. Replacing Nd with Ho has the same effect and problem.