Angle effect on the estimation of exchange coupling constant J for antiferromagnetically coupled medium

Exchange coupling constant (J) is an important magnetic parameter for the design of the antiferromagnetically coupled medium. So far, the relationship between the exchange bias ${\mathrm{(H}}_{\mathrm{ex}})$ and exchange coupling constant, $H_{\mathrm{ex}}{\mathrm{=J/M}}_s\mathrm{t,}$ which is deduced from the ferromagnetic–antiferromagnetic coupled system under some conditions, was commonly used to estimate the exchange coupling constant J for such medium. This article first deduces an accurate equation of the exchange coupling constant (J) and the exchange bias $H_{\mathrm{ex}}$ for the antiferromagnetically coupled medium in different applied field directions. After considering the effect of easy axis distribution of the magnetic grains in the recording medium, the equation for the antiferromagnetically coupled medium is further revised as $H_{\mathrm{ex}}{\mathrm{=aJ/M}}_s\mathrm{t.}$ a is a constant and depends on the easy axes distribution of magnetic grains, the exchange coupling constant, and the ratio of magnetic parameters between the two magnetic layers. a is found to range from 0.2 to 0.5 for isotropic media to oriented medium. The J value may have been heavily underestimated before by using the previous equation.