So when looking at a hysteresis loop, the x-axis is the magnitude of H-field, and the y-axis is the magnitude of B-field. H is in units of electricity and B is in units of magnetic flux density. My question relates to how coercivity is determined if the material being magnetized has a relative permeability greater than one. Alnico has a relative permeability of 4, and air has a relative permeability of 1. If you're trying to calculate the magnetic flux required to demagnetize the Alnico block, you can use B=uH. If the alnico block is surrounded by air, would you use u=1 or u=4 to find the coercive flux?