Magnetic Characteristics of Single-Block and Multi-Block Nd-Fe-B Permanent Magnets at Low Temperature

Abstract

Based on the intrinsic temperature dependence of permanent magnet (PM) materials, the changing magnetic characteristics of three Nd-Fe-B magnet configurations with temperature were studied. A single PM, a traditional permanent magnet guideway (PMG) with steel as the flux collector in the center of the guideway (PMG A), and a Halbach-type PMG (PMG B) were investigated in cooling experiments. Liquid nitrogen was used to cool the PM and the PMGs from room temperature to the low temperature of 77 K, while the temperature and magnetic field signals were collected simultaneously. The results show that, with the temperature decrease, both the single PM and PMGs have a significant increase in their magnetic fields, which reach peak values. The magnetic flux density of the traditional PMG A shows a more significant increase of 20.3%, while the growth rates of the single cylinder PM and PMG B are 11.1% and 8.4%, respectively. As the temperature drops below a certain value, a spin-reorientation effect takes place inside the PM and causes a rapid decline of the magnetic flux density. Finally, compared with the magnetic field value at room temperature, the magnetic field variation of the single PM, PMG A, and PMG B were 5.7% decrease, 4.3% increase, and 0.7% decrease, respectively. The results provide basic data on the variation of magnetic characteristics of PM and PMG with temperature and contribute to research on superconducting levitation systems.