Simplified expression of shielded MR head response for double-layer perpendicular medium

An approximated simple expression of MR head response was given for perpendicular double-layer media. The equation was derived by modifying Fan's equation so as to be of a nonintegral form. The validity was confirmed by comparisons with exact solutions of the Fan's equation, which resulted in errors of less than 10% for practical applications of recent MR heads. Using the expression, the reciprocity theorem revealed that the measured transition length of perpendicular recording was extremely small, less than 10 nm.