Shock induced Nd₂Fe₁₄B magnetic transition based on molecular field theory analysis

According to the shock wave experiment on the Nd₂Fe₁₄B ferromagnet, the relationship between pressure and temperature on the shock front is calculated in a pressure range from 3.3 GPa to 7.2 GPa. In order to analyze the magnetic transition mechanism of Nd₂Fe₁₄B under different temperatures and applied pressures, the equivalent pressure field is introduced to improve the two-sublattice model based on the molecular field theory. The pressure dependence of magnetostriction coefficient, susceptibility, magnetization, and Curie temperature of Nd₂Fe₁₄B are calculated. The criteria of the ferromagnetic-paramagnetic phase transition occurring in Nd₂Fe₁₄B at different temperatures and pressures are obtained. The results indicate that the Curie temperature of Nd₂Fe₁₄B decreases as pressure increases. The Curie temperature reduces from 584 K at 0 GPa to 298 K at 1.142 GPa. With the increasing of pressure, the magnetization of Nd₂Fe₁₄B declines. The critical demagnetization pressure of Nd₂Fe₁₄B also decreases with the increasing of temperature. In a pressure region from 3.3 GPa to 7.2 GPa, there appears the pressure induced ferromagnetic-paramagnetic phase transition of Nd₂Fe₁₄B.