Investigation on intergrain exchange coupling of nanocrystalline permanent magnets by Henkel plot

In a real magnet, the relation between isothermal remanence Jr(H) and dc demagnetization remanence Jd(H) is expressed as δm(H)=[Jd(H)−Jr(∞)+2Jr(H)]/J(∞). It is believed that nonzero δm is due to the interactions between particles in the magnet. Using Pr2Fe14B as a sample, the relation is examined by the micromagnetic finite element method. The positive value of δm is primarily caused by intergrain exchange coupling. The decrease of intergrain exchange coupling results in the drop of the maximum value of δm. However, the variation of anisotropy in grain boundaries produces no change in the maximum value of δm. A Henkel plot is suggested to be effective for checking intergrain exchange coupling in magnets.