Effect of magnetostriction on bias fields in self-biased MR heads

Abstract

The effect of magnetostriction on the bias conditions in self-biased magnetoresistive (MR) heads is reported. In self-biased MR heads where the bias field is derived from the sense current, the optimum bias point is where the head delivers the maximum output per unit input current. The optimum point depends on the element and head geometry, demagnetizing effects, and the permeability of the MR film. During head construction and operation the MR film is subjected to various sources of stress which can directly affect the permeability of the film and thus the position of this optimum bias point. Many self-biased MR heads were fabricated using MR elements made from thin (<1000 Å) oriented NiFe films with the magnetostriction coefficient close to but varied around zero. The results show quite a marked effect and a correlation between as-deposited measurements and completed device performance. When the magnetostriction is negative the bias current has to be driven to higher values to achieve the defined optimum. This is attributed to an increase in the net value of Hk (permeability decrease) by compressive stresses. The converse is found to be true for positive magnetostriction films.