Slope at Coercivity:

The slope of the M-H loops as well as the coercivity of the materials has good correlation with the exchange coupling between the adjacent grains in the recording media. It is known that the materials required for the application of recording media should have fine particles which are well isolated from each other. In such scenario, the exchange coupling between the grains strongly depends on the grain boundary thickness. The exchange coupling between the grains is indirectly calculated from a parameter called slope at coercivity, which is defined as.

(35.2)

The values of a required for recording are reported to be between 1.5 and 3. Honda et al [1] showed a good correlation between the slope at coercivity, exchange constant and the coercivity of the medium. It was reported that with increasing the exchange constant, the values of loop slope increases significantly and at the same time, the coercivity of the media decreased largely due a strong exchange coupling between the grains. With increasing the loop slope, the noise in the recording media increases due to the exchange coupling. Hence, the study of control of the loop slope at coercivity in relation with the exchange coupling between the grains provides a good understanding between the microstructure and magnetic properties of the nanogranular thin films.

References:

[1]. N. Honda, IEEE trans. Magn. 38 (2002) 1615.